TY - JOUR
T1 - α-Adrenergic receptor responsiveness is preserved during prolonged exercise
AU - DeLorey, Darren S.
AU - Hamann, Jason J.
AU - Valic, Zoran
AU - Kluess, Heidi A.
AU - Clifford, Philip S.
AU - Buckwalter, John B.
PY - 2007/1
Y1 - 2007/1
N2 - Our laboratory has previously reported a decline in sympathetic nervous system restraint of skeletal muscle blood flow during prolonged mild-intensity exercise. This decline may be explained by a decrease in α1- and α2-adrenergic receptor responsiveness over time. Thus the purpose of the present study was to investigate the effect of exercise duration on α1- and α2-adrenergic receptor responsiveness during prolonged constant-load exercise. Mongrel dogs (n = 6) 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 α1- (phenylephrine) α2-adrenergic-receptor (clonidine) agonists, and tyramine (to evoke endogenous norepinephrine release) were infused following 5, 30 and 50 min of mild-intensity treadmill exercise (3 miles/h), with hindlimb blood flow (HBF) and mean arterial pressure (MAP) monitored continuously. Vascular conductance (VC) was calculated as HBF/MAP. While the dogs ran on the treadmill at 3 miles/h, infusion of phenylephrine resulted in similar decreases in VC after 5 [73% (SD 10)], 30 [76% (SD 9)], and 50 [73% (SD 10)] min of exercise. Infusion of the α2-agonist clonidine also produced similar decreases in VC after 5 [58% (SD 10)], 30 [58% (SD 11)], and 50 [53% (SD 12)] min of exercise. Infusion of tyramine resulted in similar decreases in VC after 5 [55% (SD 15)], 30 [51% (SD 10)], and 50 [50% (SD 7)] min of exercise. These results demonstrate that α1- and α2-adrenergic receptor responsiveness to infusion of selective α1- and α2-adrenergic-receptor agonists and endogenous norepinephrine release (tyramine) does not decline during prolonged mild-intensity exercise. Thus a decrease in α-adrenergic receptor responsiveness over time does not appear to be responsible for the decrease in sympathetic restraint of muscle blood flow during prolonged exercise.
AB - Our laboratory has previously reported a decline in sympathetic nervous system restraint of skeletal muscle blood flow during prolonged mild-intensity exercise. This decline may be explained by a decrease in α1- and α2-adrenergic receptor responsiveness over time. Thus the purpose of the present study was to investigate the effect of exercise duration on α1- and α2-adrenergic receptor responsiveness during prolonged constant-load exercise. Mongrel dogs (n = 6) 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 α1- (phenylephrine) α2-adrenergic-receptor (clonidine) agonists, and tyramine (to evoke endogenous norepinephrine release) were infused following 5, 30 and 50 min of mild-intensity treadmill exercise (3 miles/h), with hindlimb blood flow (HBF) and mean arterial pressure (MAP) monitored continuously. Vascular conductance (VC) was calculated as HBF/MAP. While the dogs ran on the treadmill at 3 miles/h, infusion of phenylephrine resulted in similar decreases in VC after 5 [73% (SD 10)], 30 [76% (SD 9)], and 50 [73% (SD 10)] min of exercise. Infusion of the α2-agonist clonidine also produced similar decreases in VC after 5 [58% (SD 10)], 30 [58% (SD 11)], and 50 [53% (SD 12)] min of exercise. Infusion of tyramine resulted in similar decreases in VC after 5 [55% (SD 15)], 30 [51% (SD 10)], and 50 [50% (SD 7)] min of exercise. These results demonstrate that α1- and α2-adrenergic receptor responsiveness to infusion of selective α1- and α2-adrenergic-receptor agonists and endogenous norepinephrine release (tyramine) does not decline during prolonged mild-intensity exercise. Thus a decrease in α-adrenergic receptor responsiveness over time does not appear to be responsible for the decrease in sympathetic restraint of muscle blood flow during prolonged exercise.
KW - Blood flow
KW - Functional sympatholysis
KW - Skeletal muscle
KW - Sympathetic nervous system
KW - Vascular conductance
UR - http://www.scopus.com/inward/record.url?scp=33846254192&partnerID=8YFLogxK
U2 - 10.1152/ajpheart.00787.2006
DO - 10.1152/ajpheart.00787.2006
M3 - Article
C2 - 16951042
AN - SCOPUS:33846254192
SN - 0363-6135
VL - 292
SP - H392-H398
JO - American Journal of Physiology - Heart and Circulatory Physiology
JF - American Journal of Physiology - Heart and Circulatory Physiology
IS - 1
ER -