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 prevent the rise in peripheral vascular resistance that normally occurs during acclimatization. Sixteen eumenorrheic women were studied at sea level (SL) and at 4,300 m (days 3 and 10). Volunteers were randomly assigned to take the selective alpha(1)-blocker prazosin or placebo. Venous compliance, forearm 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) x 100 ml tissue(-1) x min(-1) at SL, means +/- SD). Altitude interacted with prazosin treatment (P < 0.0001) such that compliance 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 day 3 at 4,300 m, all women had significant falls in resistance (35.2 +/- 13.2 vs. 54.5 +/- 16.1 mmHg x ml(-1) x min(-1) at SL) and rises in blood flow (2.5 +/- 1.0 vs. 1.6 +/- 0.5 ml. 100 ml tissue(-1) x min(-1) at SL). By day 10, resistance and flow returned toward SL, but this return was less in the prazosin-treated group (resistance: 39.8 +/- 4.6 mmHg x ml(-1) x min(-1) with prazosin vs. 58.5 +/- 9.8 mmHg x ml(-1) x min(-1) with placebo; flow: 1.9 +/- 0.7 ml. 100 ml tissue(-1) x min(-1) with prazosin vs. 2.3 +/- 0.3 ml x 100 ml tissue(-1) x min(-1) with placebo, P < 0.05). Lower resistance related to higher circulating epinephrine in both groups (r = -0.50, P < 0.0001). Higher circulating norepinephrine related to lower venous compliance in the placebo-treated group (r = -0.42, P < 0.05). We conclude that alpha(1)-adrenergic stimulation modulates peripheral vascular changes during acclimatization.
Zamudio
S
S
Women's Health Research Center, University of Colorado Health Sciences Center, Denver, 80262, USA. Stacy.Zamudio@uchsc.edu
Douglas
M
M
Mazzeo
R S
RS
Wolfel
E E
EE
Young
D A
DA
Rock
P B
PB
Braun
B
B
Muza
S R
SR
Butterfield
G E
GE
Moore
L G
LG
D000064:Acclimatization / Q000187:drug effects* / Q000502:physiology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000328:Adult; D000531:Altitude; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004837:Epinephrine / Q000097:blood; D005260:Female; D005542:Forearm / Q000502:physiology; D006801:Humans; D009638:Norepinephrine / Q000097:blood; D010991:Plethysmography; D011224:Prazosin / Q000494:pharmacology*; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology; D014680:Veins / Q000502:physiology
D000317:Adrenergic alpha-Antagonists; D009638:Norepinephrine; D011224:Prazosin; D004837:Epinephrine