Endogenous hormones subtly alter women's response to heat stress

Abstract

The thermoregulatory responses of menstruant women to exercise in dry heat (dry-bulb temperature/wet-bulb temperature = 48/25 degrees C) were evaluated at three times during the menstrual cycle: menstrual flow (MF), 3-5 days during midcycle including ovulation (OV), and in the middle of the luteal phase (LU). Serum concentrations of estradiol-17 beta (E2), progesterone (Pg), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) were measured by radioimmunoassay, and these values were used to determine the dates of OV (peak LH and FSH) and LU (peak postovulatory Pg). After heat acclimation, subjects received heat stress tests (HST) consisting of a 2-h cycle-ergometer exercise at 30% of maximal O2 consumption in the heat. Rectal (Tre) and mean skin (Tsk) temperatures, heart rate (HR), and sweat rate on the chest and thigh were recorded continuously. Total sweat loss (Msw), as indicated by weight loss, was recorded every 20 min, and equivalent water replacement was given. Steady-state exercise metabolic rate (M) was measured at 45 and 110 min. Seven of eight subjects had ovulatory cycles during experimental months. At rest, Tre was lowest at OV and significantly higher at LU. During steady-state exercise both Tre and Tsk were lowest at OV and significantly higher at LU. There were no differences between phases in Msw, sweat rate on the chest and thigh or M. Despite higher Tre and Tsk at LU, all subjects were able to complete the 2-h of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

The thermoregulatory consequences of heat stroke: Are cytokines involved?

“…Second, the CTM value of 40.4 1C was based on an exhaustive heat stroke model in rats, whereas many models and instances of heat stroke are of a passive nature (Chiu et al, 1995(Chiu et al, , 1996Haveman et al, 1996;Kao and Lin, 1996;Leon et al, 2005;Lin et al, 1994Lin et al, , 1997Liu et al, 2000;Romanovsky and Blatteis, 1996;Wilkinson et al, 1988;Wright, 1976;Wright et al, 1977). Third, noted species (Hutchison, 1961), strain (Furuyama, 1982), seasonal (Hoar, 1955;Hutchison, 1961), circadian (Hutchison, 1961;Kosh and Hutchison, 1968;Wright et al, 1977), photoperiod (Hutchison, 1961), geographic (Carter et al, 2005;Hutchison, 1961) and sex effects (Aoki et al, 1998;Carpenter and Nunneley, 1988;Furuyama, 1982;Lublin et al, 1995;Ohara et al, 1975;Mehnert et al, 2002) on heat susceptibility suggest that considerable variability of CTM will exist between studies depending on one or all of these factors. For example, the lowest observed CTM in passively heat stressed mice is 40.7 1C (unpublished observations).…”

Effect of the menstrual cycle on performance of intermittent, high-intensity shuttle running in a hot environment

“…O 2 max) and progressive high intensity running was unaffected by menstrual cycle phase (Lebrun et al 1995;Lynch and Nimmo 1998). However, very few studies (Horvath and Drinkwater 1982;Carpenter and Nunneley 1988;Stephenson and Kolka 1988) have examined performance in the follicular and luteal phases of the menstrual cycle in the heat, despite numerous international competitions being organised in hot climates. From the studies that have been undertaken it was concluded that cycling and walking performance were unaffected by menstrual phase.…”

“…From the studies that have been undertaken it was concluded that cycling and walking performance were unaffected by menstrual phase. In addition, it has been shown that during submaximal cycling in the heat for acclimatised subjects, deep body temperature may be higher during the luteal compared with the follicular phase (Carpenter and Nunneley 1988). For unacclimatised subjects reports are controversial, with deep body temperature reported to be higher (Stephenson and Kolka 1988) or unaffected by menstrual phase (Wells and Horvath 1974;Horvath and Drinkwater 1982).…”

Aging and assessment of physiological strain during exercise-heat stress

“…The effects of different hormone replacement therapies for middleaged women on the thermoregulatory system during rest and exercise in the heat have also been studied extensively during the last decade (3,4,8,25). Analysis of circulating estrogen and progesterone during heat stress showed that an increased progesterone-to-estrogen ratio during the luteal phase was associated with an elevated T c (5). However, elevated circulating levels of unopposed estrogen in middle-aged women at rest and during EHS were associated with a lower regulated T c (25).…”