Effects of human menstrual cycle on thermoregulatory vasodilation during exercise

Summary

To investigate the effects of the menstrual cycle and of exercise intensity on the relationship between finger blood flow (FBF) and esophageal temperature (T_es), we studied four women, aged 20–32 years. Subjects exercised at 40% and 70%$\dot V_{O_{2_{\max } } }$ in the semi-supine posture at an ambient temperature of 20‡ C. Resting T_es was higher during the luteal phase than the follicular phase (P<0.01). There were no significant differences between the two phases in FBF, oxygen consumption, carbon dioxide production, heart rate or minute ventilation at rest and during exercise, respectively. Each regression line of the FBF-T_es relationship consists of two distinct segments of FBF change to T_es (slope 1 and 2). FBF increased at a threshold T_es for vasodilation ([T_{es 0}]) and the rate of FBF rise became greater at another T_es above this threshold ([T_{es 0}']). For both levels of exercise, [T_{es 0}] and [T_{es 0}'] were shifted upward during the luteal phase, but the slopes of the FBF-T_es relationship were almost the same in the two phases of the menstrual cycle. Increasing exercise intensity induced a significant decrease in slope 1 of the FBF-T_es relationship during the follicular (P<0.01) and the luteal phases (P<0.02), respectively. These results show that the set-point temperature may be shifted towards a higher level during the luteal phase of the menstrual cycle during exercise and that, as in males, the thermoregulatory vasodilator response is attenuated by increasing exercise-induced vasoconstrictor tone in proportion to exercise intensity during both phases of the menstrual cycle when heat storage is insufficient in women.