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Women at Altitude: Effects of Menstrual Cycle Phase and Alpha-Adrenergic Blockage on High Altitude Acclimatization.

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Annual rept.,

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Little is known concerning the effects of high altitude exposure in women. In year 1, we evaluate the effects of menstrual cycle phase on high altitude acclimatization. Results indicated that the effects of the menstrual cycle were modest on the ventilatory, circulatory and metabolic responses hypoxia but that the volume regulatory adjustments were altered such that there tended to be greater fluid retention in the luteal phase subjects.The purpose of the studies conducted in year 2 the present annual report was to determine the role of alpha-1 adrenergic activity and its interaction with menstrual cycle phase in early altitude acclimatization. Fifteen young women were exposed to an effective altitude of 300 m in the USARIEM hyperbaric chamber for 52 hr on two occasions, once while being treated with an alpha-1 blocker prazosin in a randomized, double blind fashion. Definite alpha-1 adrenergic blockade was achieved as demonstrated by a rightward shift in the blood pressure response to an a-a alpha-adrenergic agonist, phenylephrine. Prazosin blocked the altitude- associated rise in systemic blood pressure during exercise and after tilt Hematocrit was lower in a-blocked than placebo-treated subjects, implying a relaxation of venous tone, but this effect appeared similar at low and high altitudes. Ventilation, hypoxic and hypercapnic ventilatory responses were unaffected by alpha-1 adrenergic blockade at either altitude. Analyses are continuing on other variables. Thus, the information obtained to a suggests that alpha-1 adrenergic activation is a key factor in orthostatic and exercise-related elevations in blood pressure at high altitude, in keeping with the study hypothesis.

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  • Medicine and Medical Research
  • Stress Physiology

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