Effects of prolactin and progesterone on preputial gland growth and progesterone metabolism in hypophysectomized, ovariectomized immature rats

Abstract

Using a 2 × 2 factorial experimental design, treatments of hypophysectomized, ovariectomized, immature rats with prolactin (100 μg twice daily) and progesterone (2mg/day) resulted in a significant synergism between the two hormones on preputial gland wet weights. Prolactin or progesterone treatment alone, caused gland wet weights to be significantly greater than those of controls. Investigations of the possible modes of action of prolactin on the preputial gland showed that prolactin decreased serum testosterone and/or 17β-hydroxy-5α-androstan-3-one levels but had no effect on serum progesterone levels, indicating that the effect of prolactin is not mediated via an elevation in these serum steroid levels. Prolactin increased the overall rate of metabolism of [ 14C]-progesterone by preputial gland tissue in vitro in proportion to its ability to increase wet weights of the glands, but did not alter the pattern of this metabolism. In vivo progesterone treatment caused a significant change in the pattern of [ 14C]-progesterone metabolites in vitro. The main metabolites whose rates of formation were increased by progesterone treatment, were identified as 20α-hydroxy-5α-pregnan-3-one and 5α-pregnan-3α-20α-diol along with its 3β epimer. A less abundant metabolite, whose formation was diminished by progesterone treatment, was identified as 3α-hydroxy-5α-pregnan-20-one. The removal of the adrenal glands did not alter the effects of in vivo progesterone treatment on the preputial gland. Therefore, the data indicate that prolactin and progesterone exert separate effects on the preputial gland of the immature rat.