Estrogen modifies the temperature effects of progesterone

Abstract

To test the hypothesis that progestin-mediated increases in resting core temperature and the core temperature threshold for sweating onset are counteracted by estrogen, we studied eight women (24 ± 2 yr) at 27°C rest, during 20 min of passive heating (35°C), and during 40 min of exercise at 35°C. Subjects were tested four times, during the early follicular and midluteal menstrual phases, after 4 wk of combined estradiol-norethindrone (progestin) oral contraceptive administration (OC E+P), and after 4 wk of progestin-only oral contraceptive administration (OC P). The order of the OC P and OC E+P were randomized. Baseline esophageal temperature (Tes) at 27°C was higher ( P < 0.05) in the luteal phase (37.08 ± 0.21°C) and in OC P (37.60 ± 0.31°C) but not during OC E+P (37.04 ± 0.23°C) compared with the follicular phase (36.66 ± 0.21°C). Tes remained above follicular phase levels throughout passive heating and exercise during OC P, whereas Tes in the luteal phase was greater than in the follicular phase throughout exercise ( P < 0.05). The Testhreshold for sweating was also greater in the luteal phase (38.02 ± 0.28°C) and OC P (38.07 ± 0.17°C) compared with the follicular phase (37.32 ± 0.11°C) and OC E+P (37.46 ± 0.18°C). Progestin administration raised the Testhreshold for sweating during OC P, but this effect was not present when estrogen was administered with progestin, suggesting that estrogen modifies progestin-related changes in temperature regulation. These data are also consistent with previous findings that estrogen lowers the thermoregulatory operating point.