Role of endogenous female hormones in hypoxic chemosensitivity.

Effective alveolar ventilation and hypoxic ventilatory response (HVR) are higher in females than in males and after endogenous or exogenous elevation of progesterone and estrogen. The contribution of normal physiological levels of ovarian hormones to resting ventilation and ventilatory control and whether their site(s) of action is central and/or peripheral are unclear. Accordingly, we examined resting ventilation, HVR, and hypercapnic ventilatory responses (HCVR) before and 3 wk after ovariectomy in five female cats. We also compared carotid sinus nerve (CSN) and central nervous system translation responses to hypoxia in 6 ovariectomized and 24 intact female animals. Ovariectomy decreased serum progesterone but did not change resting ventilation, end-tidal PCO2, or HCVR (all P = NS). Ovariectomy reduced the HVR shape parameter A in the awake (38.9 +/- 5.5 and 21.2 +/- 3.0 before and after ovariectomy, respectively, P < 0.05) and anesthetized conditions. The CSN response to hypoxia was lower in ovariectomized than in intact animals (shape parameter A = 22.6 +/- 2.5 and 54.3 +/- 3.5 in ovariectomized and intact animals, respectively, P < 0.05), but central nervous system translation of CSN activity into ventilation was similar in ovariectomized and intact animals. We concluded that ovariectomy decreased ventilatory and CSN responsiveness to hypoxia, suggesting that the presence of physiological levels of ovarian hormones influences hypoxic chemosensitivity by acting primarily at peripheral sites.