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 phy siological levels of ovarian hormones to resting ventilation and venti latory control and whether their site(s) of action is central and/or p eripheral are unclear. Accordingly, we examined resting ventilation, H VR, 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 s erum progesterone but did not change resting ventilation, end-tidal Pc o(2), or HCVR (all P = NS). Ovariectomy reduced the HVR shape paramete r A in the awake (38.9 +/- 5.5 and 21.2 +/- 3.0 before and after ovari ectomy, respectively, P < 0.05) and anesthetized conditions. The CSN r esponse to hypoxia was lower in ovariectomized than in intact animals (shape parameter A = 22.6 +/- 2.5 and 54.3 +/- 3.5 in ovariectomized a nd intact animals, respectively, P < 0.05), but central nervous system translation of CSN activity into ventilation was similar in ovariecto mized and intact animals. We concluded that ovariectomy decreased vent ilatory and CSN responsiveness to hypoxia, suggesting that the presenc e of physiological levels of ovarian hormones influences hypoxic chemo sensitivity by acting primarily at peripheral sites.