Progesterone metabolism by rat oral mucosa II. The effect of pregnancy

In order to examine the effect of pregnancy on the gingiva, the metabolism of progesterone in pregnant and non-pregnant rats was studied. Homogenates and mitochondrial, microsomal, and soluble fractions were obtained with differential centrifugation. The subcellular preparations were supplemented with NADPH and incubated with ¹⁴C-progesterone for 30 min at pH 7.4 and 37°C. The metabolites were identified by column and multiple thin-layer chromatography and radioautography and quantified with liquid scintillation counting. The metabolism was significantly reduced in homogenate, mitochondrial, and microsomal incubations of oral mucosae of pregnant rats when compared to those of non-pregnant ones. The decrease of the metabolism in the soluble fraction incubations was not statistically significant. In all subcellular preparations the activities of 20et-and 20 β -hydroxysteroid dehydrogenases, if present, remained rather constant, but the activities of steroid hydrogenases and 3α- and 3 β -hydroxysteroid dehydrogenases decreased markedly. The value of these findings as a contributing factor in pregnancy gingivitis is discussed.