Journal of Applied Physiology, Vol 67, Issue 5 1754-1758, Copyright © 1989 by American Physiological Society
Effect of a synthetic progestin on ventilatory response to hypoxia in anesthetized rats
H. Kimura, M. Mikami, T. Kuriyama and Y. Fukuda
Department of Chest Medicine and Physiology II, School of Medicine, Chiba University, Japan.
Effects on ventilatory responses to progressive isocapnic hypoxia of a
synthetic potent progestin, chlormadinone acetate (CMA), were determined in
the halothane-anesthetized male rat. Ventilation during the breathing of
hyperoxic gas was largely unaffected by treatment with CMA when carotid
chemoreceptor afferents were kept intact. The sensitivity to hypoxia
evaluated by hyperbolic regression analysis of the response curve did not
differ between the control and CMA groups. The reduction of ventilation
after bilateral section of the carotid sinus nerve (CSN) in hyperoxia was
less severe in CMA-treated than in untreated animals. Furthermore, the
CMA-treated rats showed a larger increase in ventilation during the hypoxia
test and a lower PO2 break point for ventilatory depression. Inhibition of
hypoxic ventilatory depression by CMA persisted even after the denervation
of CSN. We conclude that exogenous progestin likely protects regulatory
mechanism(s) for respiration against hypoxic depression through a
stimulating action independent of carotid chemoreceptor afferents and
without a change in the sensitivity of the ventilatory response to hypoxia.
