Ventilatory response of rabbits and goats to chronic progesterone administration

We assessed the ventilatory response to chronic progesterone administration of 37 male rabbits and 4 castrated male goats. Rabbits, in response to 2.72 mg.kg-1.day-1 of progesterone, did not chronically hyperventilate as measured by changes in CSF [HCO-3]. Two goats given 10 mg/kg/day of progesterone by intramuscular injection, alone or in combination with estradiol or testosterone, manifested no convincing ventilatory changes. Two goats were given progesterone in the form of progesterone-containing Silastic implants. Serum progesterone levels of 8-27 ng/ml were maintained over the course of 45 days. The hyperventilation in these goats, unlike that of man, was slow to develop (8-15 days), slow to decay (10-30 days), and relatively small (resting PETCO2 fell 3-5 mm Hg relative to control); and there was no change in slope of the CO2 response curves. We conclude that goats and rabbits do not respond to progesterone like man, and therefore are not good models with which to study the mechanism(s) by which progesterone produces hyperventilation in man.