Effect of propranolol on sympathetically‐mediated leg vasoconstriction in humans

Sympatho‐excitatory maneuvers have traditionally been used to study vascular responsiveness in humans, but it is unclear if circulating epinephrine masks peripheral vasoconstriction during these maneuvers. We hypothesized that the vasoconstrictor response to 3 conventional sympatho‐excitatory maneuvers (neck pressure, unilateral thigh cuff release, and isometric hand‐grip) would be greater after the administration of the beta‐adrenergic blocker propranolol. Twelve healthy subjects (21–33 yrs) underwent these maneuvers while beat‐by‐beat mean arterial blood pressure (finger photoplethysmography), femoral mean blood velocity (Doppler ultrasound), and femoral artery diameter (edge‐detection software) were measured. Femoral vascular conductance was calculated as flow/pressure. Propranolol had no effect on baseline blood pressure or femoral vascular conductance ( P >0.05). As a result of neck pressure, femoral artery vascular conductance was reduced 23.6 ± 3.8 % before versus 29.9 ± 3.4 % after infusion of propranolol ( P = 0.11). After unilateral thigh cuff release, femoral vascular conductance was reduced 41.4 ± 10.8 % before versus 61.9 ± 8.4 % after propranolol infusion ( P = 0.17). During isometric hand‐grip exercise, femoral vascular conductance was reduced 51.8 ± 4.7 % before versus 54.5 ± 2.6 % after administration of propranolol ( P = 0.62). Thus, it does not appear that epinephrine alters the vascular responses to these sympatho‐excitatory maneuvers. Supported by AHA grant 555623Z