Women at altitude: forearm hemodynamics during acclimatization to 4,300 m with alpha(1)-adrenergic blockade

We hypothesized that blockade of alpha (1)-adrenergic receptors would preve nt the rise in peripheral vascular resistance that normally occurs during a cclimatization. Sixteen eumenorrheic women were studied at sea level (SL) a nd at 4,300 m (days 3 and 10). Volunteers were randomly assigned to take th e selective alpha (1)-blocker prazosin or placebo. Venous compliance, forea rm vascular resistance, and blood flow were measured using plethysmography. Venous compliance fell by day 3 in all subjects (1.39 +/- 0.30 vs. 1.62 +/ - 0.43 ml.Delta 30 mmHg(-1).100 ml tissue(-1).min(-1) at SL, means +/- SD). Altitude interacted with prazosin treatment (P < 0.0001) such that complia nce returned to SL values by day 10 in the prazosin-treated group (1.68 +/- 0.19) but not in the placebo-treated group (1.20 +/- 0.10, P < 0.05). By d ay 3 at 4,300 m, all women had significant falls in resistance (35.2 +/- 13 .2 vs. 54.5 +/- 16.1 mmHg.ml(-1.)min(-1) at SL) and rises in blood flow (2. 5 +/- 1.0 vs. 1.6 +/- 0.5 ml.100 ml tissue(-1).min(-1) at SL). By day 10, r esistance and flow returned toward SL, but this return was less in the praz osin-treated group (resistance: 39.8 +/- 4.6 mmHg.ml(-1).min(-1) with prazo sin vs. 58.5 +/- 9.8 mmHg.ml(-1).min(-1) with placebo; flow: 1.9 +/- 0.7 ml .100 ml tissue(-1).min(-1) with prazosin vs. 2.3 +/- 0.3 ml.100 ml tissue(- 1).min(-1) with placebo, P < 0.05). Lower resistance related to higher circ ulating epinephrine in both groups (r = -0.50, P < 0.0001). Higher circulat ing norepinephrine related to lower venous compliance in the placebo-treate d group (r = -0.42, P < 0.05). We conclude that <alpha>(1)-adrenergic stimu lation modulates peripheral vascular changes during acclimatization.