Progesterone-induced hyperventilation in the guinea pig

Progesterone-induced hyperventialtion has thus far not been reported in animals other than humans. Accordingly we investigated the effects of chronic progesterone treatment on ventilation in guinea pigs. Virgin female guinea pigs were divided into those treated with cholesterol as controls (C), progesterone (P), or estrogen plus progesterone (E&P). All hormones were administered in silastic capsules placed subcutaneously for 28 days. On day 28 arterial blood gases and respiratory rates were determined. Arterial pH was elevated in P- and E&P-treated animals compared with controls (7.43 ± 0.04 and 7.43 ± 0.03 vs 7.39 ± 0.05, respectively, P < 0.05). Arterial P_CO2 was reduced in both progesterone-treated groups compared to controls (33.9 ± 5.8 (P), 33.1 ± 2.8 (E&P), 38.0 ± 4.3 (C)), and was correlated with systemic progesterone concentrations in animals receiving E&P (r = -0.85, P < 0.01) but not in animals receiving P alone (r = -0.07, P = N.S.). Arterial [HCO₃ ^-], P_o2 and respiratory rates were not different between groups. We conclude that chronic progesterone administration produces hyperventilation in guinea pigs, and that estrogen facilitates this action of progesterone.