FASEB J.
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by GARCÍA, M. C.
Right arrow Articles by SEÑARÍS, R. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by GARCÍA, M. C.
Right arrow Articles by SEÑARÍS, R. M.
(The FASEB Journal. 2003;17:1392-1400.)
© 2003 FASEB

Hypothalamic levels of NPY, MCH, and prepro-orexin mRNA during pregnancy and lactation in the rat: role of prolactin

M. C. GARCÍA, M. LÓPEZ, O. GUALILLO, L. M. SEOANE, C. DIÉGUEZ and ROSA MARIA SEÑARÍS1

Department of Physiology, Faculty of Medicine, University of Santiago de Compostela, Santiago de Compostela, Spain

1Correspondence: Department of Physiology, Faculty of Medicine, University of Santiago de Compostela, R/San Francisco s/n, 15782 Santiago de Compostela, Spain. E-mail: fsrsr{at}usc.es


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Pregnancy and lactation provide excellent models of physiological hyperphagia and hyperprolactinemia. To identify possible factors associated with the increased feeding in these situations, we measured hypothalamic mRNA levels of three orexigenic neuropeptides—NPY, MCH, and orexins—in nonpregnant, pregnant, and lactating rats by in situ hybridization. NPY mRNA content in the arcuate nucleus was significantly increased during pregnancy and lactation. However, MCH and prepro-orexin expression was decreased in both states. 48 or 72 h of fasting in pregnant and lactating rats further elevated NPY mRNA levels and increased the low MCH mRNA content. Surprisingly, no effect was observed in prepro-orexin mRNA levels. Finally, we investigated the possible effect of high PRL levels on these orexigenic signals using a model of hyperprolactinemia induced by pituitary graft. NPY mRNA content was unchanged, but MCH and prepro-orexin mRNA levels were significantly decreased. Our results suggest that the increased NPY expression might be partly responsible for the hyperphagia observed during pregnancy and lactation. MCH and prepro-orexin may be involved in the adaptation of other homeostatic mechanisms and their decreased levels in these physiological settings could be mediated by the elevated circulating PRL levels. García, M. C., López, M., Gualillo, O., Seoane, L. M., Diéguez, C., Señarís, R. M. Hypothalamic levels of NPY, MCH, and prepro-orexin mRNA during pregnancy and lactation in the rat: role of prolactin.


Key Words: hypothalamus • gestation • orexigenic peptides • lactogenic hormones


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
PREGNANCY is a hypermetabolic state with a great increase in maternal body fat and weight and is associated with numerous neuroendocrine changes. During gestation, there is no increase in energy efficiency; the energy balance becomes positive at this stage, primarily because of an increase in food intake, which is necessary to prevent the depletion of maternal energy stores (1) . Failure to increase fat mass during pregnancy causes considerable neonatal and maternal morbidity. On the other hand, lactation has a profound effect on energy homeostasis (2) . Hyperphagia is the first and most important component of the concerned responses that are mounted to meet the greatly increased energy demands in the lactating rat (3) . The mechanisms by which maternal weight and food intake are regulated are poorly understood and likely different in these two physiological situations. In pregnancy the hyperphagia is present despite a marked increase in circulating leptin levels whereas lactating rats are normo- or hypolipidemic (4 , 5) .

Numerous hypothalamic neuropeptides, including neuropeptide Y (NPY), melanin-concentrating hormone (MCH), and orexins, have been involved in the control of food intake as well as in the regulation of neuroendocrine functions. These neuropeptides have been reported to display orexigenic functions and to be regulated by leptin levels. Nutritional status can alter the expression of these appetite-regulating peptides, but most studies have investigated acute changes with fasting, and the effects of a long-term state of hyperphagia as gestation and lactation remain to be fully defined.

The expression of NPY in the arcuate nucleus (ARC) has been shown to clearly increase with food restriction (6 , 7) and its levels to be negatively regulated by leptin (8 , 9) . In addition to its role in appetite regulation, NPY subserves other functions and has been implicated in the regulation of LH secretion, particularly the generation of the preovulatory surge of LH (10) .

MCH is a newly identified peptide synthesized in neurons of the lateral hypothalamus that appears to be an important regulator of energy homeostasis. Studies investigating the effect of MCH have produced conflicting results, with initial indications of an inhibitory effect on food intake (11) ; more recent data suggest a stimulatory role (12) . MCH gene knockout mice are hypophagic and lean, supporting the notion that this neuropeptide stimulates food intake (13) .

Recently, orexins have been described as novel neuropeptides controlling food intake and localized within and around the lateral hypothalamic area (LHA) (14 , 15) . Orexins have been shown to increase food intake if administered in the third ventricle (15) , and prepro-orexin (prepro-OX) mRNA is increased in food -restricted animals (16) . Conversely, orexin levels decrease with leptin treatment in rats (16 , 17) .

Pregnancy and lactation are accompanied by numerous changes in hormone secretion that participate in the adaptation of the mother to the gestational and lactating condition. The hyperprolactinemia exhibited in both states likely plays an important role in regulating numerous brain functions, including feeding and appetite (18) .

Our main goal in this work was to gain further insight into the mechanisms responsible for the physiological hyperphagia observed during pregnancy and lactation. Specifically, we tested the hypothesis that the hyperphagia present in these physiological settings could be driven by increased expression of orexigenic neuropeptides. For this issue, we measured the mRNA levels of the neuropeptides mentioned above in the hypothalamus of fed and fasted pregnant and lactating rats. We also investigated the possibility that elevated prolactin (PRL) levels during pregnancy and lactation might influence the expression of these neuropeptides using a well-characterized model of hyperprolactinemia induced by pituitary graft in virgin ovariectomized female rats.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Animals
Pregnancy and lactation
Female Sprague-Dawley rats (250–300 g) (supplied by the breeding facility of the University of Santiago, Spain) were used for the experiments. The animals were housed under controlled lighting (12 h light: 12 h dark) and temperature, with free access to food and water. On the day of proestrous, three females were housed with a male, and the day when sperm was observed in the vaginal smear was designated as day 0 of pregnancy. Rats at gestational day 18 (pregnant rats) and at postpartum day 14 (lactating rats) were used. Nonpregnant rats in proestrous were used as controls. For studies during lactation, the number of pups of each pregnant rat that delivered at our facilities was adjusted to 10 on day 2 postpartum. For fasting experiments, pregnant and lactating rats were deprived of food with free access to water for 48 or 72 h. At least six animals were used for each experimental group. Animals were killed by decapitation, and their brains were removed and immediately frozen into dried ice.

Induction of hyperprolactinemia by pituitary graft
Female Sprague-Dawley rats (130–150 g) were used for this experiment. All animals were bilaterally ovariectomized or sham-operated under ketamine-xylazine anesthesia (4 mg/kg). Ovariectomy was conducted in order to obtain a result independent from the ovaric function. One group of six rats received two pituitary glands obtained from two rats of the same age and sex, under de kidney capsule. Animals were killed 4 days after the surgery procedure and whole blood was used for serum collection and subsequently PRL RIA. The completeness of graft acceptance was determined for each animal by autopsy. Animal studies were approved by the Ethics Committee of the University of Santiago de Compostela and experiments were performed in agreement with the rules of laboratory animal care and the international law on animal experimentation.

Serum leptin determination
Serum leptin levels were measured by RIA as described (19) using a rat leptin RIA kit (Linco Research, Inc., St. Louis, MO, USA). The limit of sensitivity was 0.5 µg/L. The intra- and interassay coefficients of variation for concentrations of 1.6 µg/L and 11.6 µg/L were 2.4% and 4.6%, and 4.8% and 5.7%, respectively.

Serum PRL determination
Serum PRL was determined as described previously (20) by means of double antibody RIA using materials and protocols by Dr. A. F. Parlow (National Hormone and Pituitary Program of NIDDK, Baltimore, MD, USA). All samples were assayed in duplicate within one assay and results were expressed in terms of the NIDDK PRL-RP-3 standard.

In situ hybridization
For in situ hybridization, coronal hypothalamic sections (16 µm thick) were cut on a cryostat, mounted onto gelatin-coated slides, and immediately stored at -80°C until hybridization. NPY and MCH mRNA levels were determined using specific antisense oligodeoxynucleotide probes (for NPY, 5'-AGATGAGATGTGGGGGGAAACTAGGAAAAG-3', gene bank accession number: M20373 and for MCH, 5'-CCAACAGGGTCGGTAGACTCGTCCCAGCAT-3', gene bank accession number: M2971). The probes were 3'-end labeled with 35S-{alpha}dATP using terminal deoxynucleotidyl transferase. The specificity of the probes was confirmed by performing cohybridization studies, incubating the sections with an excess of unlabeled probes (data not shown). In situ hybridization was performed as described previously (21 , 22) . Tissue sections were fixed with 4% paraformaldehyde in 0.1M phosphate buffer (pH 7.4) at room temperature for 30 min, dehydrated through 70, 80, 90, 95%, and absolute ethanol (5 min each).

Hybridization was carried out overnight at 37°C in a moist chamber. Hybridization solution was applied onto each slide and contained 4x SSC, 50% deionized formamide, 1x Denhardt’s solution, 10 µg /mL sheared single-stranded salmon sperm DNA, 10% dextran sulfate, DTT 50 mM, and ~1x106 cpm/slide of the labeled probes. After hybridization, sections were rinsed in 1xSSC at room temperature, then sequentially washed in 1xSSC at 42°C (30 min/wash, 4 washes in total); 1xSSC at room temperature for 1 h, then rinsed in 70% ethanol with 300 mM ammonium acetate. Finally, sections were air-dried and exposed to Hyperfilm ß-Max at room temperature for 3–5 days.

For prepro-OX mRNA detection we used a prepro-OX antisense riboprobe labeled with 35S-CTP. A sense riboprobe was used as a negative control. The specificity of the probe has been demonstrated (16) . Frozen sections were fixed with 4% paraformaldehyde in 0.1M phosphate buffer (pH 7.4) at room temperature for 30 min, dehydrated through 70, 80, 90, 95%, and absolute ethanol (5 min each). Hybridization was carried out overnight at 55°C in a moist chamber. Hybridization solution contained 4x SSC, 50% deionized formamide, 1x Denhardts solution, 10 µg/mL sheared single-stranded salmon sperm DNA, 10% dextran sulfate, 5 µg/mL of tRNA, and 1x106 cpm/slide of the labeled probe. After hybridization, sections were rinsed in 2xSSC at room temperature, then sequentially washed in 2xSSC/50% formamide at 55°C (15 min/wash, 2 washes in total); rinsed briefly in 2xSSC at 37°C, incubated in RNase buffer containing 20 µg/mL Rnase A at 37°C (30 min), rinsed in 2xSSC at 37°C, washed three times in 2x SSC/50% formamide at 55°C (15 min per wash), twice in 2x SSC at room temperature (5 min per wash), and rinsed in water and ethanol. Finally, sections were air-dried and exposed to Hyperfilm ß-Max at room temperature for 7 days.

To compare anatomically similar regions, slides were matched according to the rat atlas of Paxinos and Watson (23) . Sections from at least three animals per experimental group were processed together and were always apposed to the same autoradiographic film. Autoradiographic signals were analyzed using an imaging densitometer and the computer program Molecular AnalystTM (Bio-Rad Laboratories, Hercules, CA, USA). The background pixel density for each section was measured and the specific signal was corrected by subtracting this background value.

The slides were finally developed in Kodak D-19 developer (Kodak, Rochester, NY, USA), fixed (Kodak, Rochester, NY, USA), and counterstained with methylene blue.

Statistical analysis
Data were expressed as mean ± SE and analyzed with a computerized package of statistical analysis. Statistical significance of the differences was determined using the nonparametric Mann-Whitney test. A P value <0.05 was considered as a criterion of significance.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
In agreement with previous reports (24) , in situ hybridization with an oligoprobe for NPY mRNA showed NPY mRNA positive cells in the arcuate (ARC) and dorsomedial nucleus (DMH) of the hypothalamus. The highest density of positive cells was located in the ARC (Fig. 1 ).



View larger version (56K):
[in this window]
[in a new window]
  		Figure 1. Upper panel: Autoradiographic images of representative coronal brain sections incubated with a 35S-labeled antisense oligonucleotide probe for NPY (A) or for MCH (B) or a 35S-labeled antisense mRNA probe for prepro-OX (C). Areas delineated in the sections are shown at higher magnification. ARC = arcuate nucleus, DMH = dorsomedial nucleus, LH = lateral hypothalamus, and 3V = third ventricle. Lower panel: Brightfield photomicrographs showing representative silver grain clusters for NPY (D), MCH (E), and prepro-OX (F) mRNA.

In situ hybridization with an oligoprobe for MCH and a riboprobe for prepro-OX mRNA demonstrated labeling of numerous cells in the lateral hypothalamus (LH) (Fig. 1) , as has already been reported (25 , 26) .

Regulation of the hypothalamic mRNA levels of NPY, MCH, and prepro-OX during pregnancy
Serum leptin levels significantly increased in pregnant rats in relation to nonpregnant rats (control); food-deprived pregnant rats had significantly lower serum leptin levels than nonrestricted animals (Fig. 2 A).



View larger version (42K):
[in this window]
[in a new window]
  		Figure 2. A) Serum leptin concentrations in nonpregnant (NP), pregnant rats (P), and 48 and 72 h fasted pregnant animals (P+FAST 48H and P+FAST72H). Bars represent mean ± SE. **P< 0.01 vs. nonpregnant rats and ##P<0.01 vs. pregnant rats. B) NPY mRNA levels in the ARC of nonpregnant and pregnant rats. Data (mean±SE) were expressed as % change in relation to nonpregnant rats. **P<0.01 vs. nonpregnant animals. C) NPY mRNA levels in the ARC of fed and 48 and 72 h fasted pregnant rats. Data (mean±SE) were expressed as % change in relation to pregnant rats. *P <0.01, ***P <0.001 vs. pregnant animals. B, C) Right panels: Autoradiographic images of representative coronal brain sections incubated with a 35S-labeled antisense oligonucleotide probe for NPY at the level of the ARC and DMH of the described experimental groups. Areas delineated in the sections are shown at higher magnification.

We found increased levels of NPY mRNA content in the ARC of the hypothalamus compared with the levels observed in control nonpregnant rats (% of control: 131.20±10.58%, P<0.01) (Fig. 2B ). In contrast, no effect was observed in the NPY mRNA content in the DMH. Fasting of pregnant rats for 48 or 72 h further increased NPY mRNA levels in the ARC of the hypothalamus compared with pregnant rats fed ad libitum (% change: 128±15.19%, P<0.05; and 276.80±16.72%, P<0.001 for 48 and 72 h fasted pregnant animals, respectively, vs. fed pregnant animals) (Fig. 2C ). No increase was observed in the DMH of the hypothalamus of pregnant rats upon fasting.

MCH mRNA levels in the LH of pregnant rats were significantly decreased compared with control nonpregnant rats (% of control: 25.06±18.14%, P<0.001) (Fig. 3 A). Prepro-OX mRNA content was also decreased in the LH (% of control: 6.23 ±5.703%, P<0.001) (Fig. 3B ). Fasting increased MCH mRNA levels in the LH in the pregnant rats (% change: 233.04±30.64%, P<0.001; and 283.04±22.44%, P<0.001 for 48 and 72 h fasted animals vs. fed animals) (Fig. 3C ), but failed to modify the expression of prepro-OX (Fig. 3D ).



View larger version (50K):
[in this window]
[in a new window]
  		Figure 3. Left panels: A) MCH and B) prepro-OX mRNA levels in the LH in nonpregnant (NP) and pregnant (P) rats. Data (mean±SE) were expressed as % change in relation to nonpregnant rats. ***P<0.001 vs. nonpregnant animals. C) MCH and D) prepro-OX mRNA levels in fed (P) and 48 and 72 h fasted pregnant rats (P+FAST 48H and P+FAST 72H). Data (mean±SE) were expressed as % change in relation to pregnant rats fed ad libitum. ***P <0.001 vs. fed animals. A—D) Right panels: Autoradiographic images of representative coronal brain sections incubated with a 35S-labeled antisense oligonucleotide for MCH or a 35S-labeled antisense prepro-OX mRNA probe at the level of the LH.

Regulation of the hypothalamic mRNA levels of NPY, MCH, and prepro-OX during lactation
During lactation serum leptin levels were restored to nonpregnant values and food-deprived lactating rats had significantly lower serum leptin levels compared with nonrestricted animals (Fig. 4 A).



View larger version (33K):
[in this window]
[in a new window]
  		Figure 4. A) Serum leptin concentrations in nonpregnant rats (NP), lactating rats (L14) and 48 and 72 h fasted lactating animals (L14+FAST 48H and L14+FAST 72H). Bars represent mean ± SE. **P< 0.01 vs. nonpregnant rats. B) NPY mRNA levels in the ARC and DMH of nonpregnant and lactating rats. Data (mean±SE) were expressed as % change in relation to nonpregnant rats. **P<0.01 and ***P<0.001 vs. nonpregnant animals. C) NPY mRNA levels in the ARC of fed and 48 and 72 h fasted lactating rats. Data (mean±SE) were expressed as % change in relation to lactating rats fed ad libitum. *P<0.05, **P <0.01 vs. fed animals. B, C) Left panels: Autoradiographic images of representative coronal brain sections incubated with a 35S-labeled antisense oligonucleotide probe for NPY at the level of the ARC and DMH of the described experimental groups. Areas delineated in the sections are shown at higher magnification.

There was a significant increase in the NPY mRNA content in the ARC (% of control:149.53±7.90%, P<0.001) and DMH (% of control:197.55±19.73%, P<0.001) of lactating rats in relation to nonpregnant rats (Fig. 4B ). These levels further increase upon fasting in the ARC (% change: 157.94±21.83%, P<0.05 and 241.57±39.48%, P<0.01, for 48 and 72 h fasted lactating vs. fed lactating animals) (Fig. 4C ), but no effect of food deprivation was observed in the DMH under these experimental conditions.

MCH mRNA levels were significantly decreased during lactation (% of control: 60.97±18.41%, P<0.01), and fasting (72 h) induced a clear increase in the expression of this peptide (% change: 178.12±4.22% for fasted lactating vs. fed lactating animals, P<0.01) (Fig. 5 A, C).



View larger version (46K):
[in this window]
[in a new window]
  		Figure 5. A) MCH and B) prepro-OX mRNA levels in the LH of nonpregnant (NP) and lactating (L14) rats. Data (mean±SE) were expressed as % change in relation to nonpregnant rats. *P<0.05 and **P<0.01 vs. nonpregnant animals. C) MCH and D) prepro-OX mRNA levels in fed (L14) and 48 and 72 h fasted lactating rats (L14+FAST 48H and L14+FAST72H). Data (mean±SE) were expressed as % change in relation to lactating rats fed ad libitum. *P<0.05 and **P <0.01 vs. fed animals. A—D) Right panels: Autoradiographic images of representative coronal brain sections incubated with a 35S-labeled antisense oligonucleotide for MCH, or a 35S-labeled antisense prepro-OX mRNA probe at the level of the LH.

Prepro-OX mRNA levels were significantly decreased during lactation (% of control: 64.38±11.15%, P<0.05), and fasting for 48 or 72 h did not induce any change in relation to fed lactating rats (Fig. 5B, D ).

Regulation of NPY, prepro-OX and MCH by prolactin
As previously reported (27) , the pituitary graft induced a large increase (P<0.01) in PRL serum levels (45.51±9.10 µg/L) vs. sham-operated (13.754±3.31 µg/L) and ovariectomized rats (6.39±2.67 µg/L). PRL levels in pituitary grafted animals were similar to the levels found in pregnant animals (33.22±5.30 µg/L) (Fig. 6 A).



View larger version (44K):
[in this window]
[in a new window]
  		Figure 6. A) Serum PRL concentrations in sham-operated (SHAM), ovariectomized (OVX) and pituitary grafted (OVX+GRAFT) rats. Bars represent mean ± SE. **P< 0.01 vs. sham-operated rats. B) Left panel: ARC NPY mRNA levels in the 3 experimental groups. Right panel: Autoradiographic images of representative coronal brain sections incubated with a 35S-labeled antisense oligonucleotide probe for NPY at the level of the ARC and DMH of the described experimental groups. Areas delineated in the sections are shown at higher magnification. C, D) Lower panel: MCH and prepro-OX mRNA levels in the LH of the 3 experimental groups. Data (mean±SE) were expressed as % change in relation to sham-operated animals. **P <0.01 and***P <0.001 vs. sham-operated rats. Upper panel: Autoradiographic images of representative coronal brain sections incubated with a 35S-labeled antisense oligonucleotide for MCH or a35S-labeled antisense prepro-OX mRNA probe at the level of the LH.

Ovariectomy and hyperprolactinemia did not produce significant differences in NPY mRNA levels in the ARC or the DMH in comparison to intact sham-operated rats (Fig. 6B ).

In contrast, a significant decrease of MCH and prepro-OX mRNA content was found in the LH of hyperprolactinemic animals in comparison with intact sham-operated rats (% of sham-operated rats: 67.46±10.02%, P<0.01 and 35.37±4.64%, P<0.001 for MCH and prepro-OX) (Fig. 6C, D ).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Pregnancy and lactation are associated with considerable metabolic demands that are met by a number of homeostatic mechanisms. There is a remarkable increase in body fat mass and body weight in the mother during gestation. In the rat, food intake increases by ~50% and food consumption usually occurs in the dark phase only (28) . During lactation there is a massive increase of food intake to a 180–450% of nonpregnant levels with a change in both night and day feeding (29) . The mechanisms involved in the regulation of the hyperphagia present in these states are still largely unknown.

Several hypothalamic neuropeptides have been identified as possible regulators of food intake and metabolism. NPY has been demonstrated to greatly increase food intake in satiated animals when injected intracerebroventricularly (30) . For this action NPY is mainly produced in the ARC nucleus of the hypothalamus, and the nerve fibers from this nucleus project into various hypothalamic sites that are implicated in the regulation of feeding behavior, in particular the paraventricular nucleus (PVN) (31) . Diet restriction and starvation rapidly induce accumulation of NPY in the PVN by increasing NPY mRNA levels in the ARC nucleus (6 , 32) . These effects are mainly due to the low levels of leptin found in these experimental conditions (33) . Our data demonstrated that NPY mRNA levels in the ARC were significantly increased during pregnancy. Taking into account the high serum leptin levels observed in late pregnant animals, this increase in hypothalamic NPY expression is somewhat surprising, since in normal nonpregnant rats modest increases in circulating leptin levels lead to a marked decrease in NPY mRNA levels in the ARC nucleus (34) . However, in pregnant rats there is also a state of leptin resistance mediated, at least in part, by a decrease in the expression of the long biologically active form of the leptin receptor (Ob-Rb) (4) .

Other workers have reported no change of NPY mRNA levels in the hypothalamus during pregnancy (29) . This disagreement may be due to the technology used: Northern blotting using RNA from the whole hypothalamus vs. in situ hybridization looking at discrete nuclei in the hypothalamus.

To gain further insight into this issue, we assessed the levels of NPY after food restriction and therefore decreased leptin levels in pregnant rats. We found that fasting for 48 or 72 h further increased NPY mRNA levels in the ARC of pregnant rats, as it occurs in the nonpregnant state (35) . It has also been shown that in food-restricted late pregnant rats there is an increase in circulating ghrelin levels (36) , and ghrelin significantly increases NPY mRNA levels in the hypothalamus (37) . Thus, a role of the high levels of ghrelin found in these food-deprived pregnant animals upon the up-regulation of NPY expression cannot be ruled out.

NPY mRNA has also been detected in the DMH, although its role in this nucleus is not clear (24) . In contrast to NPY neurons in the ARC, we could not find any change in NPY mRNA content in the DMH in fed or fasting pregnant rats. During lactation we demonstrated increased levels of NPY mRNA in both the ARC and DMH nuclei of the hypothalamus. Fasting of lactating rats further up-regulated NPY expression in the ARC, but not in the DMH. These results agree with previous reports (24 , 38) . The finding that NPY is elevated in both nuclei during lactation suggests that the mechanisms involved could be different in pregnant rats, where we found such an increase restricted to the ARC nucleus. Little is known about NPY neurons in the DMH. In the female rat, this population of neurons does not seem to be activated under basal conditions or in response to stimuli such as fasting (39) or streptozotocin-induced diabetes (40) . Lactation, then, is the only demonstrated physiological situation where NPY is up-regulated in this nucleus. Besides lactation, there are only two types of mice that exhibit increased levels of NPY mRNA in the DMH and a marked hyperphagia: the melanocortin receptor 4 (MC4-R) knockout mice and the agouti mice (41) . Whether MC4-R expression might somehow be compromised in the lactating rat and contribute to collaborate in the massive hyperphagia during this state remains to be clarified.

These data together with the central role of NPY in inducing the feeding response make this peptide a possible candidate in mediating the hyperphagia during pregnancy and lactation.

Surprisingly, the hypothalamic expression of orexin, another orexigenic peptide, was significantly decreased during pregnancy and lactation; in these two groups of rats, food restriction did not increase the levels of mRNA of this hypothalamic peptide, as has been demonstrated in nonpregnant rats (16 , 42) . These results suggest that during gestation there might be a strong inhibitory effect on prepro-OX expression at the level of the hypothalamus that counteracts the stimulatory effect of the low leptin levels observed in fasted pregnant and lactating rats; furthermore they indicate that orexin is not apparently involved in the regulation of the increased food intake observed during pregnancy and lactation.

Nevertheless, orexin has also been related to sleep. Different experimental evidences supported a possible role of the orexin system in the regulation of the sleep-wake cycle. Thus, orexin knockout mice or dogs with a mutation in the orexin receptor 2 (OX2R) display a phenotype similar to human narcolepsy (43 , 44) , characterized by excessive daytime sleepiness and other physiological manifestations of REM sleep (44) . In addition, narcoleptic humans show low orexin levels in the cephalospinal fluid (45) and a decreased number of orexin neurons in the hypothalamus (46) . These findings indicate that the loss of orexin function results in narcolepsy. Pregnancy and lactation in humans and rodents are associated with changes in sleep patterns (47) . In late pregnancy in the rat there is an enhanced sleep during the dark period and alterations and sleep loss during the daytime (48) . In the lactating rat, suckling is followed by an increased incidence of sleep (49) . The low prepro-OX expression levels observed in late pregnant and lactating animals, which were unchanged upon fasting, indicate that this neuropeptide could be another factor contributing to the sleep disturbances during these situations.

Earlier studies have shown that MCH knockout mice are hypophagic and lean (13) and MCH antagonists have been postulated as possible drugs to treat obesity (50) . Our finding of a marked decrease in MCH mRNA levels during pregnancy and lactation was rather surprising, indicating that the hyperphagia present in these physiological situations is not mediated by this orexigenic peptide. Furthermore they also suggest that, at least in some physiological settings, decreased MCH is not enough to induce hypophagia and weight loss. Nevertheless, MCH and orexins have also been shown to regulate other functions different to food intake such as stimulating the GnRH/LH system and the hypothalamic-pituitary-adrenocortical axis (HPA) (51 52 53 54) . Whether the decreased expression of these neuropeptides could contribute to regulate these functions during pregnancy and lactation remains to be established.

Pregnancy and lactation are physiological states characterized by the presence of hyperprolactinemia. Several data appear to show that PRL may be a major factor mediating the hyperphagia associated with both states (18) . In fact, there are reports indicating that PRL can induce hyperphagia when administered systemically or intracerebroventricularly (55 56 57) . Moreover, up-regulation of prolactin receptor expression in numerous hypothalamic nuclei of pregnant and lactating rats (58 , 59) suggests that a pregnant or lactating female may be significantly more sensitive to the hyperphagic effects of prolactin than a nonpregnant one. As feeding and appetite changes in response to hyperprolactinemia are likely to be mediated by the appetite centers of the brain, we tested the hypothesis that elevated PRL levels during pregnancy and lactation could affect the expression of the above mentioned neuropeptides, using a pituitary grafted rat model of chronic hyperprolactinemia.

Our data showing no differences in the levels of NPY mRNA in the ARC and DMH between hyperprolactinemic and sham-operated rats suggest that prolactin could not be involved in NPY overexpression in the hypothalamus observed during pregnancy and lactation. It has been reported that during lactation the suckling induced hyperprolactinemia does not participate in the increase in ARC NPY expression. In contrast to our results, it has been shown that the high PRL levels induced by suckling play a major stimulatory role in the increase of NPY mRNA content in the DMH (60) . The reason for this discrepancy is unclear at present.

Finally, the decreased MCH and prepro-OX mRNA levels induced by pituitary graft indicate that the inhibition of these peptides during pregnancy and lactation could be mediated at least in part by PRL. To our knowledge this is the first report providing direct evidence for a role of PRL in regulating MCH and prepro-OX mRNA levels in the rat. These effects of PRL could be involved in the reported contribution of the hormone in the sleep alterations exhibited during pregnancy and lactation (61) and in the regulatory function of PRL on the gonadotrophin axis (62) . Additional work is required to determine the full extent of the function of PRL in mediating these effects.

In summary, this study sets the basis for a complete dissection of the complex neural pathways involved in the mechanisms established during pregnancy and lactation regarding body weight homeostasis. Specifically, we found that increased NPY gene expression during pregnancy and lactation might be part of the adaptive mechanisms present in these physiological circumstances to develop the hyperphagia observed in these states. MCH and prepro-OX do not appear to be responsible for the alterations in body weight homeostasis present in pregnancy and lactation, though they may well be involved in the adaptation of other homeostatic mechanisms that occur in these situations. Increased circulating PRL levels could contribute to the decreased MCH and prepro-OX levels observed in these states.

Received for publication September 25, 2002. Accepted for publication March 27, 2003.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Richard, D., Trayhurn, P. (1985) Energetic efficiency during pregnancy in mice fed ad libitum or pair-fed to the normal energy intake of unmated animals. J. Nutr. 115,593-600
  2. Trayhurn, P. (1989) Thermogenesis and energetics of pregnancy and lactation. Can. J. Physiol. Pharmacol. 67,370-375[Medline]
  3. Roberts, S. B., Coward, W. A. (1984) Lactation increases the efficiency of energy utilization in rats. J. Nutr. 114,2193-2200
  4. García, M. C., Casanueva, F. F., Dieguez, C., Señarís, R. M. (2000) Gestational profile of leptin messenger ribonucleic acid (mRNA) content in the placenta and adipose tissue in the rat, and regulation of the mRNA levels of the leptin receptor subtypes in the hypothalamus during pregnancy and lactation. Biol. Reprod. 62,698-703[Abstract/Free Full Text]
  5. Brogan, R. S., Mitchell, S. E., Trayhurn, P., Smith, M. S. (1999) Suppression of leptin during lactation: contribution of the suckling stimulus versus milk production. Endocrinology 140,2621-2627[Abstract/Free Full Text]
  6. White, J. D., Kershaw, M. (1990) Increased hypothalamic neuropeptide Y expression following food deprivation. Mol. Cell Neurosci. 1,41-48
  7. Lewis, D. E., Shellard, L., Koeslag, D. G., Boer, D. E., McCarthy, H. D., McKibbin, P. E., Russel, J. C., Williams, G. (1993) Intense exercise and food restriction cause similar hypothalamic neuropeptide Y increase in rats. Am. J. Physiol. 264,E279-E284
  8. Stephens, T. W., Basinski, M., Bristow, P. K., Bue-Valleskey, J. M., Burgett, S. G., Craft, L., Hale, J., Hoffmann, J., Hsiung, H. M., Kriauciunas, A., et al (1995) The role of neuropeptide Y in the antiobesity action of the obese gene product. Nature (London) 377,530-534[CrossRef][Medline]
  9. Schwartz, M. W., Baskin, D. G., Bukowski, T. R., Kuijper, J. L., Foster, D., Lasser, G., Prunkard, D. E., Porte, D., Woods, S. C., Seeley, R. J., et al (1996) Specificity of leptin action on elevated blood glucose levels and hypothalamic neuropeptide Y gene expression in ob/ob mice. Diabetes 45,531-535[Abstract]
  10. Xu, M., Hill, J. W., Levine, J. E. (2000) Attenuation of luteinizing hormone surges in neuropeptide Y knockout mice. Neuroendocrinology 72,263-271[CrossRef][Medline]
  11. Presse, F., Sorokovsky, I., Max, J. P., Nicolaidis, S., Nahon, J. L. (1996) Melanin-concentrating hormone is a potent anorectic peptide regulated by food-deprivation and glucopenia in the rat. Neuroscience 71,735-745[CrossRef][Medline]
  12. Rossi, M., Choi, S. J., OShea, D., Miyoshi, T., Ghatei, M. A., Bloom, S. R. (1997) Melanin-concentrating hormone acutely stimulates feeding, but chronic administration has no affect on body weight. Endocrinology 138,351-355[Abstract/Free Full Text]
  13. Shimada, M., Tritos, N. A., Lowell, B. B., Flier, J. S., Maratos-Flier, E. (1998) Mice lacking melanin concentrating-hormones are hypophagic and lean. Nature (London) 396,670-674[CrossRef][Medline]
  14. deLecea, L., Kilduff, T., Peyron, C., Gao, X., Foye, P., Danielson, P., Fukuhara, C., Battenberg, E., Gautvi k, K., Suttcliffe, J. (1998) The hypocretins: hypothalamus-specific peptides with neuroexcitatory activity. Proc. Natl. Acad. Sci. USA 95,322-327[Abstract/Free Full Text]
  15. Sakurai, T., Amemiya, A., Ishii, M., Matsuzaki, I., Chemelli, R., Tanaka, H., Williams, S., Richardson, J., Kozlowski, G., Wilson, S., et al (1998) Orexins and orexin receptors: a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behavior. Cell 92,573-585[CrossRef][Medline]
  16. López, M., Seoane, M., García, M., Lago, F., Casanueva, F., Señarís, R., Diéguez, C. (2000) Leptin reverses fasting-induced increase in prepro-orexin mRNA and orexin Receptor 1 mRNA levels in the rat hypothalamus. Biochem. Biophys. Res. Commun. 269,41-45[CrossRef][Medline]
  17. Beck, B., Richy, S. (1999) Hypothalamic hypocretin /orexin and neuropeptide Y: divergent interaction with energy depletion and leptin. Biochem. Biophys. Res. Commun. 258,119-122[CrossRef][Medline]
  18. Grattan, D. R. (2001) The actions of prolactin in the brain during pregnancy and lactation. Prog. Brain Res. 133,153-171[Medline]
  19. Pinilla, L., Seoane, L. M., Gonzalez, L., Carro, E., Aguilar, E., Casanueva, F. F., Dieguez, C. (1999) Regulation of serum leptin levels by gonadal function in rats. Eur. J. Endocrinol. 140,468-473[Abstract]
  20. Coya, R., Alvarez, C. V., Gianzo, C., Dieguez, C. (1999) Effect of TGF-ß1 on prolactin synthesis and secretion: an in vitro study. J. Neuroendocrinol. 11,351-360[CrossRef][Medline]
  21. Señarís, R. M., Lago, F., Coya, R., Pineda, J., Dieguez, C. (1996) Regulation of hypothalamic somatostatin, growth hormone-releasing hormone, and growth hormone receptor messenger ribonucleic acid by glucocorticoids. Endocrinology 137,5236-5241[Abstract]
  22. López, M., Seoane, L. M., García, M. C., Dieguez, C., Señarís, R. (2002) Neuropeptide Y, but not agouti-related peptide or melanin-concentrating hormone, is a target peptide for orexin-A feeding actions in the rat hypothalamus. Neuroendocrinology 75,34-44[CrossRef][Medline]
  23. Paxinos, G., Watson, C. (1986) The Rat Brain in Stereotaxic Coordinates Academic Press Sydney, Australia.
  24. Li, C., Chen, P., Smith, M. S. (1998) Neuropeptide Y (NPY) neurons in the arcuate nucleus (ARH) and dorsomedial nucleus (DMH), areas activated during lactation, project to the paraventricular nucleus of the hypothalamus. Regul. Pept. 75-76,93-100
  25. Griffond, B., Ciofi, P., Bayer, L., Jacquemard, C., Fellmann, D. (1997) Immunocytochemical detection of the neurokinin B receptor (NK3) on melanin-concentrating hormone (MCH) neurons in rat brain. J. Chem. Neuroanat. 12,183-189[CrossRef][Medline]
  26. Broberger, C. (1999) Hypothalamic cocaine- and amphetamine-regulated transcript (CART) neurons: histochemical relationship to thyrotropin-releasing hormone, melanin-concentrating hormone, orexin/hypocretin and neuropeptide Y. Brain Res 848,101-113[CrossRef][Medline]
  27. Gualillo, O., Lago, F., García, M., Menéndez, C., Señarís, R., Casanueva, F. F., Diéguez, C. (1999) Prolactin stimulates leptin secretion by rat white adipose tissue. Endocrinology 140,5149-5153[Abstract/Free Full Text]
  28. Cripps, A. W., Williams, V. J. (1975) The effect of pregnancy and lactation on food intake, gastrointestinal anatomy and absorptive capacity of the small intestine in the albino rat. Br. J. Nutr. 33,17-32[CrossRef][Medline]
  29. Wilding, J. P. H., Ajala, M. O., Lambert, P. D., Bloom, S. R. (1997) Additive effects of lactation and food restriction to increase hypothalamic neuropeptide Y mRNA in rats. J. Endocrinol. 152,365-369[Abstract]
  30. Stanley, B. G., Kyrkouli, S. E., Lampert, S., Leibowitz, S. F. (1986) Neuropeptide Y chronically injected into the hypothalamus: a powerful neurochemical inducer of hyperphagia and obesity. Peptides 7,1189-1192[CrossRef][Medline]
  31. Bai, F. L., Yamano, M., Shiotani, Y., Emson, P. C., Smith, A. D., Powell, J. F., Tohyama, M. (1985) An arcuato-paraventricular and dorsomedial hypothalamic neuropeptide system which lacks noradrenaline in the rat. Brain Res 331,172-175[CrossRef][Medline]
  32. Sahu, A., Kalra, P. S., Kalra, S. P. (1988) Food deprivation and ingestion induce reciprocal changes in neuropeptide Y concentrations in the paraventricular nucleus. Peptides 9,83-86[CrossRef][Medline]
  33. Korner, J., Savontaus, E., Chua, S. C., Jr, Leibel, R. L., Wardlaw, S. L. (2001) Leptin regulation of Agrp and NPY mRNA in the rat hypothalamus. J. Neuroendocrinol. 13,959-966[CrossRef][Medline]
  34. Dhillon, H., Ge, Y., Minter, R. M., Prima, V., Moldawer, L. L., Muzyczka, N., Zolotukhin, S., Kalra, P. S., Kalra, S. P. (2000) Long-term differential modulation of genes encoding orexigenic and anorexigenic peptides by leptin delivered by rAAV vector in ob/ob mice. Relationship with body weight change. Regul. Pept. 92,97-105[CrossRef][Medline]
  35. Schwartz, M. W., Sipols, A. J., Grubin, C. E., Baskin, D. G. (1993) Differential effect of fasting on hypothalamic expression of genes encoding neuropeptide Y, galanin, and glutamic acid decarboxylase. Brain Res. Bull. 31,361-367[CrossRef][Medline]
  36. Gualillo, O., Caminos, J. E., Nogueiras, R., Seoane, L. M., Arvat, E., Ghigo, E., Casanueva, F. F., Diéguez, C. (2002) Effect of food restriction on ghrelin in normal-cycling female rats and in pregnancy. Obes. Res. 10,682-687[Medline]
  37. Seoane, L. M., López, M., Tovar, S., Casanueva, F. F., Señarís, R., Diéguez, C. (2003) Agouti-related peptide, neuropeptide Y, and somatostatin-producing neurons are targets for ghrelin actions in the rat hypothalamus. Endocrinology 144,544-551[Abstract/Free Full Text]
  38. Li, C., Chen, P., Smith, S. (1998) The acute suckling stimulus induces expression of neuropeptide Y (NPY) in cells in the dorsomedial hypothalamus and increases NPY expression in the arcuate nucleus. Endocrinology 139,1645-1652[Abstract/Free Full Text]
  39. Sahu, A., Kalra, P. S., Kalra, S. P. (1988) Food deprivation and ingestion induce reciprocal changes in neuropeptide Y concentrations in the paraventricular nucleus. Peptides 9,83-86
  40. Marks, J. L., Waite, K., Li, M. (1993) Effects of streptozotocin-induced diabetes mellitus and insulin treatment on neuropeptide Y mRNA in the rat hypothalamus. Diabetologia 36,497-502[Medline]
  41. Kesterson, R. A., Huszar, D., Lynch, C. A., Simerly, R. B., Cone, R. D. (1997) Induction of neuropeptide Y gene expression in the dorsal medial hypothalamic nucleus in two models of the agouti obesity syndrome. Mol. Endocrinol. 11,630-637[Abstract/Free Full Text]
  42. Mondal, M. S., Nakazato, M., Date, Y., Murakami, N., Yanagisawa, M., Matsukura, S. (1999) Widespread distribution of orexin in rat brain and its regulation upon fasting. Biochem. Biophys. Res. Commun. 256,495-499[CrossRef][Medline]
  43. Chemelli, R. M., Willie, J. T., Sinton, C. M., Elmquist, J. K., Scammell, T., Lee, C., Richardson, J. A., Williams, S. C., Xiong, Y., Kisanuki, Y., et al (1999) Narcolepsy in orexin knock-out mice: molecular genetics of sleep regulation. Cell 98,437-451[CrossRef][Medline]
  44. Lin, L., Faraco, J., Li, R., Kadotani, H., Rogers, W., Lin, X., Qiu, X., de Jong, P. J., Nishino, P., Mignot, E. (1999) The sleep disorder canine narcolepsy is caused by a mutation in the hypocretin (orexin) receptor 2 gen. Cell 98,365-376[CrossRef][Medline]
  45. Nishino, S., Ripley, B., Overeem, S., Nevsimalova, S., Lammers, G. J., Vankova, J., Okun, M., Rogers, W., Brooks, S., Mignot, E. (2001) Low cerebrospinal fluid hypocretin (Orexin) and altered energy homeostasis in human narcolepsy. Ann. Neurol. 50,381-388[CrossRef][Medline]
  46. Thannickal, T. C., Moore, R. Y., Nienhuis, R., Ramanathan, L., Gulyani, S., Aldrich, M., Cornford, M., Siegel, J. M. (2000) Reduced number of hypocretin neurons in human narcolepsy. Neuron 27,469-474[CrossRef][Medline]
  47. Santiago, J. R., Nolledo, M. S., Kinzler, W., Santiago, T. (2001) Sleep and sleep disorders in pregnancy. Ann. Intern. Med. 134,396-408[Abstract/Free Full Text]
  48. Kimura, M., Zhang, S. Q., Inoue, S. (1996) Pregnancy-associated sleep changes in the rat. Am. J. Physiol. 271,R1063-R1069[Medline]
  49. Voloschin, L. M., Tramezzani, J. H. (1979) Milk ejection reflex linked to slow wave sleep in nursing rats. Endocrinology 105,1202-1207[Abstract]
  50. Takekawa, S., Asami, A., Ishihara, Y., Terauchi, J., Kato, K., Shimomura, Y., Mori, M., Murakoshi, H., Kato, K., Suzuki, N., et al (2002) T-226296: a novel, orally active and selective melanin-concentrating hormone receptor antagonist. Eur. J. Pharmacol. 438,129-135[CrossRef][Medline]
  51. Murray, J. F., Adan, R. A., Walker, R., Baker, B. I., Thody, A. J., Nijenhuis, W. A., Yukitake, J., Wilson, C. A. (2000) Melanin-concentrating hormone, melanocortin receptors and regulation of luteinizing hormone release. J. Neuroendocrinol. 12,217-223[CrossRef][Medline]
  52. Pu, S., Jain, M. R., Kalra, P. S., Kalra, S. P. (1998) Orexins, a novel family of hypothalamic neuropeptides, modulate pituitary luteinizing hormone secretion in an ovarian steroid-dependent manner. Regul. Pept. 78,133-136[CrossRef][Medline]
  53. Bluet-Pajot, M. T., Presse, F., Voko, Z., Hoeger, C., Mounier, F., Epelbaum, J., Nahon, J. L. (1995) Neuropeptide-E-I antagonizes the action of melanin-concentrating hormone on stress-induced release of adrenocorticotropin in the rat. J. Neuroendocrinol. 7,297-303[CrossRef][Medline]
  54. Jaszberenyi, M., Bujdoso, E., Pataki, I., Telegdy, G. (2000) Effects of orexins on the hypothalamic-pituitary-adrenal system. J. Neuroendocrinol. 12,1174-1178[CrossRef][Medline]
  55. Gerardo-Gettens, T., Moore, B. J., Stern, J. S., Horwitz, B. A. (1989) Prolactin stimulates food intake in the absence of ovarian progesterone. Am. J. Physiol. 256,R701-R706
  56. Gerardo-Gettens, T., Moore, B. J., Stern, J. S., Horwitz, B. A. (1989) Prolactin stimulates food intake in a dose-dependent manner. Am. J. Physiol. 256,R276-R280
  57. Sauve, D., Woodside, B. (1996) The effect of central administration of prolactin on food intake in virgin female rats is dose-dependent, occurs in the absence of ovarian hormones and the latency to onset varies with feeding regimen. Brain Res 729,75-81[Medline]
  58. Sugiyama, T., Minoura, H., Kawabe, N., Tanaka, M., Nakashima, K. (1994) Preferential expression of the long form prolactin receptor mRNA in the rat brain during oestrous cycle, pregnancy and lactation: hormones involved in its gene expression. J. Endocrinol. 141,325-333[Abstract]
  59. Pi, X. J., Grattan, D. R. (1999) Increased expression of both short and long forms of prolactin receptor mRNA in the hypothalamic nuclei of lactating rats. J. Mol. Endocrinol. 23,13-22[Abstract]
  60. Li, C., Chen, P., Smith, S. (1999) Neuropeptide Y and tuberoinfundibular dopamine activities are altered during lactation. Role of prolactin. Endocrinology 140,118-123[Abstract/Free Full Text]
  61. Zhang, S. Q., Kimura, M., Inoue, S. (1999) Effects of prolactin on sleep in cyclic rats. Psychiatry Clin. Neurosci. 53,101-103[Medline]
  62. Smith, M. S. (1981) Site of action of prolactin in the suppression of gonadotropin secretion during lactation in the rat: effect on pituitary responsiveness to LHRH. Biol. Reprod. 24,967-976[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 EndocrinologyHome page
R. A. Augustine and D. R. Grattan
Induction of Central Leptin Resistance in Hyperphagic Pseudopregnant Rats by Chronic Prolactin Infusion
Endocrinology, March 1, 2008; 149(3): 1049 - 1055.
[Abstract] [Full Text] [PDF]

Home page
 J. Physiol.Home page
R. A. Augustine, S. R. Ladyman, and D. R. Grattan
From feeding one to feeding many: hormone-induced changes in bodyweight homeostasis during pregnancy
J. Physiol., January 15, 2008; 586(2): 387 - 397.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Endocrinol. Metab.Home page
P. Silveyra, V. Lux-Lantos, and C. Libertun
Both orexin receptors are expressed in rat ovaries and fluctuate with the estrous cycle: effects of orexin receptor antagonists on gonadotropins and ovulation
Am J Physiol Endocrinol Metab, October 1, 2007; 293(4): E977 - E985.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
E. Vigo, J. Roa, M. Lopez, J. M. Castellano, R. Fernandez-Fernandez, V. M. Navarro, R. Pineda, E. Aguilar, C. Dieguez, L. Pinilla, et al.
Neuromedin S as Novel Putative Regulator of Luteinizing Hormone Secretion
Endocrinology, February 1, 2007; 148(2): 813 - 823.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
R. Arumugam, D. Fleenor, and M. Freemark
Lactogenic and Somatogenic Hormones Regulate the Expression of Neuropeptide Y and Cocaine- and Amphetamine-Regulated Transcript in Rat Insulinoma (INS-1) Cells: Interactions with Glucose and Glucocorticoids
Endocrinology, January 1, 2007; 148(1): 258 - 267.
[Abstract] [Full Text] [PDF]

Home page
 J Mol EndocrinolHome page
G Sun, Z Tian, Y Yao, H Li, and T Higuchi
Central and/or peripheral immunoreactivity of orexin-A in pregnant rats and women
J. Mol. Endocrinol., February 1, 2006; 36(1): 131 - 138.
[Abstract] [Full Text] [PDF]

Home page
 J EndocrinolHome page
R L Bogorad, T Y Ostroukhova, A N Orlova, P M Rubtsov, and O V Smirnova
Long isoform of prolactin receptor predominates in rat intrahepatic bile ducts and further increases under obstructive cholestasis
J. Endocrinol., February 1, 2006; 188(2): 345 - 354.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
P. Chen and M. S. Smith
Regulation of Hypothalamic Neuropeptide Y Messenger Ribonucleic Acid Expression during Lactation: Role of Prolactin
Endocrinology, February 1, 2004; 145(2): 823 - 829.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by GARCÍA, M. C.