Body fluids and temperature responses of heat-exposed women before and after ovulation with and without rehydration.

1. Four females (21-25 yr) were exposed to 43.3 degrees C dry bulb, 28-29 degrees C wet bulb, for 10 hr both early and late in two menstrual cycles. During the experiments in one cycle, the subjects were rehydrated while during the experiments in another cycle, the subjects were allowed to progressively dehydrate.2. Rates of weight loss and oral temperatures were determined hourly while venous blood samples were obtained before and then after 1, 2, 3, 4, 6, 8, and 10 hr of heat exposure.3. Pre-ovulatory results were compared with post-ovulatory results and dehydration experiments with rehydration experiments. In addition, the data on these female subjects were compared with those presented elsewhere for similarly treated male subjects.4. When compared to males, these resting females did not significantly haemodilute when heat exposed. In addition, the female subjects apparently suffered a decrease in plasma volume and body water at a rate some 1.5 times that of similarly exposed males.5. In general,% change in total protein/unit volume of plasma for these female subjects was similar to previously published results for males. However, there were significant differences in the manner in which albumin and globulin fractions changed before and after ovulation.6. The rates of body weight loss for these subjects were similar to those determined for males. No difference was noted between pre- and post-ovulatory rates of weight loss. Dehydration significantly depressed the rates of weight loss during heat exposure.7. Stimulation of sweating (assessed as weight loss) appeared to require similar amounts of heat storage before and after ovulation though initial post-ovulatory temperatures were generally higher.8. Progressive dehydration of females before ovulation was accompanied by rates of increase in oral temperatures that were similar to those seen for similarly exposed males.9. When females progressively dehydrated after ovulation, there was no statistically significant correlation between temperature rise and weight loss as had been noted in pre-ovulatory experiments. In addition, for all subjects, the rise in body temperature with dehydration was less after than before ovulation. Two subjects showed an ability to decrease their body temperature in the face of continued dehydration.10. Based on these results, the differences in the responses of males and females to heat exposure were ascribed mainly to two causes: a, inherent differences such as skin surface: blood volume ratios, and b, the inability of females to maintain their vascular volume during heat exposure.