Effect of estrogen supplementation on exercise thermoregulation in premenopausal women

This study examined the effects of 3 days of estrogen supplementation (ES) on thermoregulation during exercise in premenopausal (20-39 yr) adult women during the follicular phase of the menstrual cycle. Subjects (11 control, 10 experimental) performed upright cycle ergometer exercise at 60% of maximal O₂ consumption in a neutral environment (25°C, 30% relative humidity) for 20 min. Subjects were given placebo (P) or β-estradiol (2 mg/tablet, 3 tablets/day for 3 days). All experiments were conducted between 6:30 and 9:00 AM after ingestion of the last tablet. Heart rate, forearm blood flow (FBF), mean skin temperature, esophageal temperature (T(es)), and forearm sweat rate were measured. Blood analysis for estrogen and progesterone reflected the follicular phase of the menstrual cycle. Maximal O₂ consumption (37.1 ± 6.2 in P vs. 38.4 ± 6.3 ml · kg^-1 · min^-1 in ES) and body weight-to-surface area ratio (35.58 ± 2.85 in P vs. 37.3 ± 2.7 in ES) were similar between groups. Synthesis of 70-kDa heat shock protein was not induced by 3 days of ES. Neither the threshold for sweating (36.97 ± 0.15 in P vs. 36.90 ± 0.22°C in ES), the threshold for an increase in FBF (37.09 ± 0.22 in P vs. 37.17 ± 0.26°C in ES), the slope of sweat rate- T(es) relationship (0.42 ± 0.16 in P vs. 0.41 ± 0.17 in ES), nor the FBF- T(es) relationship (10.04 ± 4.4 in P vs. 9.61 ± 3.46 in ES) was affected (P > 0.05) by 3 days of ES. We conclude that 3 days of ES by young adult women in the follicular phase of their menstrual cycle have no effect on heat transfer to the skin, heat dissipation by evaporative cooling, or leukocyte synthesis of 70-kDa heat shock protein.