(The FASEB Journal. 2008;22:1211.4.)
© 2008 FASEB
Adrenergic receptor mediated tonic vasoconstriction is not increased in skeletal muscle of older beagles
Darren DeLorey1,
John B Buckwalter2,
Scott Mittelstadt3,
Heidi A Kluess2 and
Philip S Clifford2
1 University of Alberta, Edmonton, Canada
2 Medical College of Wisconsin, Milwaukee, WI
3 Abbott, Abbott Park, IL
ABSTRACT
Aging is associated with an increase in muscle sympathetic nerve activity. Whether this increased efferent sympathetic nerve activity leads to greater tonic vasoconstriction and reduced blood flow to resting and contracting skeletal muscles in old compared to young has not been clearly established. Therefore, the purpose of the present study was to investigate the effect of aging on 
1– and 2–adrenergic receptor mediated restraint of skeletal muscle blood flow. Young (n = 6; 22 ± 3 months) and old (n = 7; 119 ± 22 months) beagles were instrumented chronically with transit-time flow probes on the external iliac arteries and an indwelling catheter in a branch of the femoral artery. On separate days, flow-adjusted doses of selective 1- (prazosin; 0.25 ug/ml/min) and 2–adrenergic-receptor (rauwolscine; 1.25 ug/ml/min) antagonists were infused at rest, and during treadmill running at 2.5 miles/h and 4 miles/h with 2.5% grade. Hindlimb blood flow (HBF) and mean arterial pressure (MAP) were monitored continuously and vascular conductance (VC) was calculated as HBF/MAP. Infusion of prazosin resulted in similar increases in VC (p > 0.05) in young and old beagles at rest (Young 100 ± 43 % ; Old:, 158 ± 84 %) and at 2.5 miles/h (Young 61 ± 28 % ; Old:, 80 ± 25 %) and 4 miles/h with 2.5% grade (Young: 36 ± 28 %; Old: 57 ± 13 %). Rauwolscine infusion also produced similar increases in VC (p > 0.05) in young and old beagles at rest (Young: 64 ± 49 %; Old: 119 ± 60 %) and at 2.5 miles/h (Young: 64 ± 20 %; Old: 86 ± 32 %) and 4 miles/h with 2.5% grade (Young: 49 ± 20 %; Old: 61 ± 11 %). These results demonstrate that 1– and 2-adrenergic receptor mediated restraint of skeletal of muscle blood flow does not increase in older compared to young beagles at rest or during dynamic exercise.
