Thermoregulation during exercise in women who are taking oral contraceptives

Abstract

Thermoregulation during exercise was studied in seven women who were taking oral contraceptive pills for 3 weeks of each month. The subjects were studied once in the 3rd week of taking the pill (P) and once during the following week when they took no pil (N). Rectal temperature (Tre), heart rate (fc) and evaporative water loss (EWL, ventilated capsule technique) were measured while they walked on a treadmill for 60 min at 4.8 km.h-1 at a 10% gradient. Ambient temperature was 22 degrees C. A venous blood sample was drawn 30 min before each experiment for measurement of hematocrit (packed cell volume, PCV), plasma osmolality (Osmpl), and plasma levels of the endogenous pyrogens interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6). Resting Tre was 0.31 degree C higher in P than in N (P < 0.01) and Tre remained higher in P throughout the entire exercise period (P < 0.01). Threshold Tre for the onset of EWL was 0.32 degree C higher in P than in N (P < 0.01). Exercise fc was 6.5 beats.min-1 higher in P than in N (P < 0.01). There was no significant difference in PCV, Osmpl, IL-1 beta or IL-6 between P and N. It was concluded that the administration of synthetic progestins in oral contraceptives causes an upward shift in the threshold for heat loss responses, resulting in higher body core temperatures both at rest and during exercise. There was no evidence that these alterations in thermoregulation were mediated by changes in body fluid balance or in plasma levels of IL-1 beta or IL-6.

Hormonal Contraception, Body Water Balance and Thermoregulation

“…In addition, there are cross-sectional studies comparing women on and off oral contraceptives on body water regulation (55-57, 79), that are consistent with our findings, suggesting that one month effects may be similar to chronic effects. However, our data cannot be extrapolated to indicate that the changes apparent after one month are similar to those during long-term oral contraceptive treatment.…”

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

“…Similarly, Rogers and Baker (1997) recorded a higher rectal temperature and heart rate when taking the contraceptive pill compared with the no pill week during treadmill walking (22 o C, 39% RH). In the current study rectal temperature was 0.1 o C higher during days 15-28, whereas in the studies comparing pill use with the pill free week temperatures were 0.3 o C higher (Martin and Buono 1997;Rogers and Baker 1997). Martin and Buono (1997) postulated that the high rectal temperature may diminish performance, however in the current study performance was actually improved.…”

“…However, during cycling for 1 h at 60% 2 O V & max in the heat (30 o C, 50% RH) rectal temperature and heart rate were greater when subjects were taking oral contraceptives in comparison with a contraceptive free week, which the authors suggested might result in reduced capacity or performance in oral contraceptive users (Martin and Buono 1997). Similarly, Rogers and Baker (1997) recorded a higher rectal temperature and heart rate when taking the contraceptive pill compared with the no pill week during treadmill walking (22 o C, 39% RH). In the current study rectal temperature was 0.1 o C higher during days 15-28, whereas in the studies comparing pill use with the pill free week temperatures were 0.3 o C higher (Martin and Buono 1997;Rogers and Baker 1997).…”

“…Furthermore, Lynch and Nimmo (1998) shown to be greater than their endogenous counterparts (Bemben 1993). Thus exogenous progestins have a significant effect upon thermoregulation (Grucza et al 1993;Rogers and Baker 1997). Both the high progestin concentration and potency of the oral contraceptives seem the likely explanation for the higher resting rectal temperatures observed.…”

Menstrual cycle and oral contraceptive use do not modify postexercise heat loss responses

“…However, it is unclear within the female population whether sex hormones associated with the menstrual cycle or oral contraceptive (OC) use significantly alter the potential for heat dissipation. If the potential for heat dissipation varies according to phase of the menstrual cycle, competitive athletes and workers could use this information to plan their exercise or work schedule to minimize risks of excessive heat retention.Blood pressure regulation (e.g., baroreflex sensitivity) (42, 43) and thermoregulatory (6,7,14,18,23,24,36,47) control are both influenced by endogenous and exogenous female sex hormones. Although Lynn et al (37) considered the effects of menstrual phase on the combined responses of blood pressure control, core temperature, and skin blood flow responses during postexercise resting, they did not measure an index of sudomotor activity despite evaporative heat loss being the primary avenue of heat dissipation during hyperthermia.…”