The effect of castration and sex steroids on ventilatory control in male guinea pigs.
Male guinea pigs (N = 7) given progesterone hyperventilate with PaCO2 falling from control levels of 39.0 +/- 0.6 (SEM) Torr to 32.0 +/- 0.7 Torr after 7 days of treatment. This response was associated with a rise in plasma progesterone concentration to approximately 15 ng ml-1 and a transient rise in plasma 17 beta-estradiol concentrations. To determine the role of the testes in generating the transient estrogen increase as well as the significance of estrogens to the progesterone response, male guinea pigs were castrated and treated either with estradiol or a placebo. Estrogen-treated castrates (N = 15) had a mean PaCO2 of 36.1 +/- 0.8 Torr and the castrates given the placebo (N = 7) had an average PaCO2 of 43.8 +/- 1.2 Torr (P less than 0.001). Both of these castrate groups were also different from intact, untreated males (P less than 0.01). Progesterone concentrations were very low and not different. When progesterone was additionally administered, the PaCO2's fell to 33.0 +/- 0.8 and 38.2 +/- 0.6 Torr for the estrogen- and placebo-treated castrate groups, respectively. The male guinea pig hyperventilates when given progesterone with the magnitude and time course of his response comparable to the human's. The response to progesterone is not critically dependent on the testes or on plasma estrogen concentrations; however, both castration and exogenous estrogen appear to influence PaCO2 without altering plasma progesterone concentrations.
D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D002369:Castration; D002784:Cholesterol / Q000494:pharmacology; D004958:Estradiol / Q000097:blood / Q000494:pharmacology*; D006168:Guinea Pigs; D006985:Hyperventilation / Q000097:blood* / Q000139:chemically induced; D008297:Male; D011374:Progesterone / Q000097:blood; D013737:Testis / Q000502:physiology
D002245:Carbon Dioxide; D011374:Progesterone; D004958:Estradiol; D002784:Cholesterol