Menstrual cycle phase and time of day alter reference signal controlling arm blood flow and sweating

Abstract

The changes occurring in the esophageal temperature (Tes) thresholds for initiation of heat loss responses as affected by the circadian period and menstrual cycle were studied. Four women exercised at 60% peak Vo2 in 35 degrees C (ambient water vapor pressure 1.73 kPa) for 30 min at 0400 and 1600 during the follicular (F) and luteal (L) phase. Tes, arm sweating rate (msw), and forearm blood flow (FBF) were measured frequently. At rest, Tes averaged 0.3 degrees C higher during L than F at both 0400 and 1600 and approximately 0.4 degrees C higher at 1600 than at 0400 during both phases. During exercise transients, the slopes of the FBF:Tes and the msw:Tes relationships were not different among treatments. The thresholds for initiation of sweating and cutaneous vasodilation were higher at 1600 than 0400 during both phases. Thresholds during F at 0400 averaged 36.44 degrees C for msw and 36.80 degrees C for vasodilation. The thresholds during L at 1600 averaged 37.46 and 37.53 degrees C for sweating and vasodilation, respectively. Our data indicate that the thermoregulatory effector activity during exercise is a function of numerous inputs, and one of these may be hormonal or hormonal-like in action. Controlling time of day and menstrual cycle phase are as important as controlling for aerobic power, age, and fitness in studying female thermoregulatory responses during exercise.

Thermoregulatory and Immune Responses During Cold Exposure: Effects of Repeated Cold Exposure and Acute Exercise

“…T sk was higher (p < 0.05) at min 0 in trial 1500 h ( = 0.4°C), but after immersion, no differences were observed between trials ( Figure 7). The gradient between T re and f sk was higher (p < 0.05) during trial 1500 h ( This study found that T re remained higher throughout the immersion period at 1500 h, compared to 0700 h. This is due to the higher initial core temperature at 1500 h vs. 0700 h, a circadian variation well documented (98,100,109). Interestingly, the change in T re during cold water immersion was greater at 1500 h. This is most likely due to the higher T re -T sk gradient at 1500 h promoting a greater transfer of heat from the core to the periphery.…”

Hormonal Contraception, Body Water Balance and Thermoregulation

“…Postmenopausal women taking combined progestin and estrogen did not exhibit the same reduction in the T es threshold for vasodilation or sweating seen in women taking only estrogen during exercise (13) suggesting that progestin blocks some of the estrogen-related thermoregulatory effects. However, Chang et al (95) failed to demonstrate a change in core temperature following three days of estrogen administration to young women in their early follicular phase, perhaps because three days of estrogen administration may not be long enough to elicit temperature changes. Conversely, another hormone, such as FSH, facilitates hypothalamic neuronal adaptation to estradiol.…”

“…Fortney et al (34) demonstrated an attenuation of the blood volume loss associated with bed rest following estrogen (premarin) administration. Some investigators have shown that plasma volume is higher during the follicular phase, when estrogen levels are rising (95,96).…”

“…Haslag and Hertzman (44) demonstrated that the onset of thermoregulatory sweating during whole body heating occurred at a lower core temperature in women during their follicular phase. Stephenson and Kolka reported lower core temperature thresholds of both sweating (53,94,95) and cutaneous vasodilation in a hot environment (94, 95) during the follicular phase. No studies have assessed directly the effect of oral contraceptives on thermoregulatory responses during exercise in the heat, but the thresholds for the onset of sweating and vasodilation were reduced by 0.47°C and 0.48°C, respectively following 2 weeks of estrogen replacement therapy in post-menopausal women (106), and was reduced during long term estrogen therapy (13).…”

“…Fortney et al (34) demonstrated an attenuation of the blood volume loss associated with bed rest following estrogen (premarin) administration. Some investigators have shown that plasma volume is higher during the follicular phase, when estrogen levels are rising (95,96).The mechanism underlying the estrogen-mediated body water retention is unclear, but may be due to alterations in the release of arginine vasopressin (8,16). No study has addressed the impact of sex hormone administration on body fluid restoration following dehydration, but arginine vasopressin measured during controlled rehydration returns to pre-dehydration levels more slowly in women (follicular phase) compared to men (89).…”