[Effects of a synthetic progestin on ventilatory response to hypoxia in awake male rats].

The effect of progesterone is most likely exact by directly stimulating the central nervous system. However, it remains unclear whether progesterone and/or estrogen act through the peripheral chemoreceptor. The carotid body is thought to be the sole sensing organ of hypoxia. The present study was conducted to determine whether administration of female hormones, i.e., progestin and/or estrogen, augment ventilatory response to hypoxia in the awake male Wistar rat. The combined administration of a synthetic progestin (TZP 4238) and estradiol for 5 days significantly increased tidal volume and minute ventilation, reduced arterial PCO2, and enhanced the ventilatory response to hypoxic gas inhalation. Augmentation of hypoxic ventilatory response was achieved by a increment of respiratory rate with a shortening of expiratory time. Administration of either TZP 4238 or estradiol alone or vehicle had no effects on respiratory variables. Our results suggest that female hormones may act through the peripheral chemoreceptor as well as the central nervous system.