Progesterone-induced changes in exercise performance and ventilatory response.

To further study the relationship between ventilatory response (VR) and exercise performance, and to investigate to what extent progesterone is responsible for ventilatory changes in the luteal phase of the menstrual cycle, we administered medroxyprogesterone acetate (MPA) to 10 normal males (20 mg three times a day for 5 doses) and compared results with those obtained in a similar study of females. With MPA, there was an increase in the resting VR to hypercapnia; the resting VR to hypoxia was not changed. There was a respiratory alkalosis at rest. During exercise, the PaCO2 remained lower but the pHa was not different because of a tendency toward lower bicarbonate concentration with MPA. Ventilation, when related to CO2 output, was increased at all exercise loads, indicating increased VR to endogenous CO2. However, ventilation was only minimally (3%) increased when related to oxygen uptake or workload. This apparent disparity is because of slightly lower CO2 output at a given oxygen uptake with MPA. As in females, maximal duration of exercise and maximal oxygen uptake were unchanged. Except for degree, MPA induced all the ventilatory changes seen in the menstrual cycle. Increased VR does not adversely affect exercise performance.