title: Catecholamine responses to alpha-adrenergic blockade during exercise in women acutely exposed to altitude.
abstract: We have previously documented the importance of the sympathetic nervous system in acclimatizing to high altitude in men. The purpose of this investigation was to determine the extent to which alpha-adrenergic blockade affects the sympathoadrenal responses to exercise during acute high-altitude exposure in women. Twelve eumenorrheic women (24.7 +/- 1.3 yr, 70.6 +/- 2.6 kg) were studied at sea level and on day 2 of high-altitude exposure (4,300-m hypobaric chamber) in either their follicular or luteal phase. Subjects performed two graded-exercise tests at sea level (on separate days) on a bicycle ergometer after 3 days of taking either a placebo or an alpha-blocker (3 mg/day prazosin). Subjects also performed two similar exercise tests while at altitude. Effectiveness of blockade was determined by phenylephrine challenge. At sea level, plasma norepinephrine levels during exercise were 48% greater when subjects were alpha-blocked compared with their placebo trial. This difference was only 25% when subjects were studied at altitude. Plasma norepinephrine values were significantly elevated at altitude compared with sea level but to a greater extent for the placebo ( upward arrow 59%) vs. blocked ( upward arrow 35%) trial. A more dramatic effect of both altitude ( upward arrow 104% placebo vs. 95% blocked) and blockade ( upward arrow 50% sea level vs. 44% altitude) was observed for plasma epinephrine levels during exercise. No phase differences were observed across any condition studied. It was concluded that alpha-adrenergic blockade 1) resulted in a compensatory sympathoadrenal response during exercise at sea level and altitude, and 2) this effect was more pronounced for plasma epinephrine.
authors.affiliation: Department of Kinesiology and Applied Physiology, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Mazzeo
authors.forename: J D
authors.initials: JD
authors.lastname: Carroll
authors.forename: G E
authors.initials: GE
authors.lastname: Butterfield
authors.forename: B
authors.initials: B
authors.lastname: Braun
authors.forename: P B
authors.initials: PB
authors.lastname: Rock
authors.forename: E E
authors.initials: EE
authors.lastname: Wolfel
authors.forename: S
authors.initials: S
authors.lastname: Zamudio
authors.forename: L G
authors.initials: LG
authors.lastname: Moore
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D000531:Altitude; D004311:Double-Blind Method; D004837:Epinephrine / Q000097:blood* / Q000652:urine; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006801:Humans; D009638:Norepinephrine / Q000097:blood* / Q000652:urine; D010101:Oxygen Consumption / Q000502:physiology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D010656:Phenylephrine; D009638:Norepinephrine; D011224:Prazosin; D004837:Epinephrine