Adrenergic tone does not tonically restrain limb venous compliance in healthy humans

Abstract

Previously we reported that sympathetic nervous system activation, induced via baroreceptor unloading, acutely decreased calf venous compliance in men. To test the hypothesis that sympathetic nervous system outflow tonically restrains limb venous compliance in healthy humans we studied 7 men (30±4 years old, mean±SE) before and during systemic alpha‐adrenergic (0.1428 mg/kg phentolamine priming dose over 5 min followed by 0.01428 mg/kg/min maintenance dose) and beta‐adrenergic blockade (0.25 mg/kg propranolol priming dose over 15 min followed by 0.004 mg/kg/min maintenance dose). Venous compliance was determined in supine subjects by inflating a thigh venous collecting cuff to 60 mmHg for 8 min, then decreasing pressure at a rate of 1 mmHg/s while measuring calf volume (strain gauge plethysmography). The slope of the pressure‐compliance relation (compliance=β1+2*β2*cuff pressure), which is the first derivative of the quadratic pressure‐volume relation [(Δ limb volume)=β0+β1*(cuff pressure)+β2*(cuff pressure)2] during reductions in collecting cuff pressure, was used to quantify venous compliance. Calf venous compliance was not increased by adrenergic blockade (−2.11±0.43 and −1.49±0.18 before and during adrenergic blockade, respectively). These data suggest that adrenergic tone does not tonically restrain calf venous compliance in healthy men.Support: NIH HL92309, AG24420 and M01 RR10732