WOMEN AT ALTITUDE: EFFECT OF ALPHA-BLOCKADE ON EXERCISE VENTILATION AT SEA LEVEL AND HIGH ALTITUDE.

Abstract

1030 Both exercise and hypoxia activate the adrenergic nervous system causing an increase in circulating catecholamines that may enhance the ventilatory response to exercise. Previous studies indicate that beta-adrenergic stimulation does not enhance the ventilatory response to exercise in normoxia or hypoxia. Weil et al. (JAP 33:1972), proposed that α-adrenergic vasoconstriction during exercise may decrease carotid body blood flow, hence augmenting chemosensitivity. Thus, blocking α1-adrenergic receptors should prevent vasoconstriction and attenuate carotid body stimulation of exercise hyperpnea. We examined the role of α-adrenergic activation during exercise in 12 women at sea level (SL) and during 40 h at simulated high altitude (HA: PB 445 mmHg) once on placebo and on an α1-adrenergic blocker (prazosin: 3mg/d). Subjects performed graded intensity cycle ergometry to exhaustion. Results ( ± S.D.): (Table)TableExercise ventilation increased (p<0.01) at HA vs. SL. However, α1-adrenergic blockade did not alter the ventilatory response to exercise in normoxic or hypoxic conditions. Thus, in humans α-adrenergic activation does not appear to augment exercise ventilation by vasoconstriction of the carotid body vasculature. Supported in part by DOD grant #DAMD 17-95-C5110