CATECHOLAMINE RESPONSE DURING 12 DAYS OF HIGH-ALTITUDE EXPOSURE (4,300 M) IN WOMEN

We have previously demonstrated that acclimatization to high altitude elicits increased sympathetic nerve activity in men. The purpose of th is investigation was to determine 1) whether women respond in a simila r manner as found previously in men and 2) the extent to which menstru al cycle phase influences this response. Sixteen eumenorrheic women (a ge, 23.6 +/- 1.2 yr; weight, 56.2 +/- 4.3 kg) were studied at sea leve l and during 12 days of high-altitude exposure (4,300 m) in either the ir follicular (F; n = 11) or luteal (L; n = 5) phase. Twenty-four-hour urine samples were collected at sea level and during each day at alti tude. Catecholamines were determined by high-performance liquid chroma tography with electrochemical detection. Compared with sea-level value s, urinary norepinephrine excretion increased significantly during alt itude exposure, peaking on days 4-6. Thereafter, levels remained const ant throughout the duration of altitude exposure. The magnitude of thi s increase was similar between the F (138%) and L (93%) phase. Urinary epinephrine levels were elevated on clay 2 of altitude exposure compa red with sea-level values for both F and L subjects (93%). Thereafter, urinary epinephrine excretion returned to sea-level values, and no di fferences were found between F and L subjects. Plasma catecholamine co ntent was consistent with urinary values and supports the concept of a n elevation in sympathetic activity over time at altitude. Mean and di astolic blood pressure as well as heart rate adjustments to high altit ude correlated significantly with urinary norepinephrine excretion-rat es. It was concluded that I)urinary and plasma catecholamine responses to 12 days of high-altitude exposure in women are similar to those pr eviously documented to occur for men; 2) whereas no differences in cat echolamine levels were observed between F-and L-phase assignments, for a given urinary norepinephrine excretion rate, blood pressure and hea rt rates were lower for F vs. L subjects; and 3) several cardiovascula r adaptations associated with high-altitude exposure correlated with 2 4-h urinary norepinephrine excretion rates and thus sympathetic nerve activity.