Catecholamine responses to {alpha}-adrenergic blockade during exercise in women acutely exposed to altitude |
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Authors: | Mazzeo Robert S; Carroll Joy D; Butterfield Gail E; Braun Barry; Rock Paul B; Wolfel Eugene E; Zamudio Stacy; Moore Lorna G |
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Abstract: | We have previouslydocumented the importance of the sympathetic nervous system inacclimatizing to high altitude in men. The purpose ofthis investigation was to determine the extent to which -adrenergicblockade affects the sympathoadrenal responses to exercise during acutehigh-altitude exposure in women. Twelve eumenorrheic women (24.7 ± 1.3 yr, 70.6 ± 2.6 kg) were studied at sea level and onday 2 of high-altitude exposure (4,300-m hypobaric chamber)in either their follicular or luteal phase. Subjects performed twograded-exercise tests at sea level (on separate days) on a bicycleergometer after 3 days of taking either a placebo or an -blocker (3 mg/day prazosin). Subjects also performed two similar exercise testswhile at altitude. Effectiveness of blockade was determined byphenylephrine challenge. At sea level, plasma norepinephrine levelsduring exercise were 48% greater when subjects were -blockedcompared with their placebo trial. This difference was only 25% whensubjects were studied at altitude. Plasma norepinephrine values weresignificantly elevated at altitude compared with sea level but to agreater extent for the placebo ( 59%) vs. blocked ( 35%) trial. Amore dramatic effect of both altitude ( 104% placebo vs. 95%blocked) and blockade ( 50% sea level vs. 44% altitude) wasobserved for plasma epinephrine levels during exercise. No phasedifferences were observed across any condition studied. It wasconcluded that -adrenergic blockade 1) resulted in acompensatory sympathoadrenal response during exercise at sea level andaltitude, and 2) this effect was more pronounced for plasma epinephrine. |
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