Esophageal temperature threshold for sweating decreases before ovulation in premenopausal women

The purpose of this study was to test the hypothesis that regulated body temperature is decreased in the preovulatory phase in eumenorrheic women. Six women were studied in both the preovulatory phase (Preov-2; days 9-12), which was 1-2 days before predicted ovulation when 17 beta-estradiol (E-2) was estimated to peak, and in the follicular phase (F; days 2-6). The subjects walked on a treadmill (similar to 225 W . m(-2)) in a warm chamber (ambient temperature = 30 degrees C; dew-point temperature = 11.5 degrees C) while heavily clothed. E-2, esophageal temperature (T-es), local skin temperatures, and local sweating rate were measured. The estimate of when the E-2 surge would occur was correct for four of six subjects. In these four subjects, E-2 increased (P less than or equal to 0.05) from 42.0 +/- 24.5 pg/ml during F to 123.2 +/- 31.3 pg/ml during Preov-2. Resting T-es was 37.02 +/- 0.20 degrees C during F and 36.76 +/- 0.28 degrees C during Preov-2 (P less than or equal to 0.05). The T-es threshold for sweating was decreased (P less than or equal to 0.05) from 36.88 +/- 0.27 degrees C during F to 36.64 +/- 0.35 degrees C during Preov-2. Both mean skin and mean body temperatures were decreased during rest in Preov-2 group. The hypothesis that regulated body temperature is decreased during the preovulatory phase is supported.