Hormonal Contraception, Body Water Balance and Thermoregulation
Annual rept. 15 Sep 1999-14 Sep 2000
JOHN B PIERCE FOUNDATION LAB NEW HAVEN CT
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To test the hypothesis that estrogen enhances water and sodium retention, we compared the fluid regulatory responses to 150 min of exercise-induced dehydration, followed by 180 min of ad libitum drinking during the follicular and luteal phases of the menstrual cycle, and following treatment with an estrogenprogestin OC EP and a progestin-only OC P oral contraceptive in a double-blind, randomized, cross-over design. We found a downward shift in osmotic regulation of arginine vasopressin AVP during the luteal phase and OC EP compared to the follicular phase during exercise, which was not accompanied by plasma volume expansion or fluid retention. 0verall fluid and electrolyte balance was similar across all trials. We also determined that the variability of the fluid regulatory hormones renin, aldosterone and atrial natriuretic peptide was high over the course of two menstrual cycles, but slopes and intercepts defining osmotic regulation of AVP were highly reliable. We also determined the estrogen and progesterone effects on thermoregulation. OC P increased core temperature and delayed the onset of sweating during exercise, but that OC EP blocks these effects. This indicates that estrogen blocks the progestin-related changes in thermoregulation. We also found that all of these effects were independent of changes in plasma volume. In our third protocol, we have found that osmotic regulation of thirst is reduced in the luteal phase compared to the follicular phase and to men, without any effects of OC P or OC EP. Fluid balance was unaffected by phase or OCs. We have not completed analysis of the AVP at this point.
- Medicine and Medical Research