Abstract. In this study the effects of hypophysectomy and autotransplantation of the pituitary gland on the concentration of hCG-binding sites (LH-receptors) and steroidogenesis in the corpus luteum and the testis of the rat were investigated. It was found that during pseudopregnancy both hCG-binding to homogenates of isolated corpora lutea and the progesterone levels in blood increase until day 7 and subsequently decrease until day 13. Hypophysectomy on day 5 led to a decrease of the number of LH-receptors and the serum progesterone level. By contrast hypophysectomy followed by autotransplantation of the pituitary gland increased the LH-receptor concentration and progesterone synthesis in spite of non-detectable LH-levels. Progesterone implants in hypophysectomized rats did not influence the number of LH-receptors. Hypophysectomy on day 0 without pituitary gland transplantation did not prevent the formation of some luteal LH-receptors measured on day 5 although progesterone was not secreted. A similar effect of prolactin secreted by pituitary autografts on LH-receptors was seen in the testis. The rapid decline of the number of binding sites normally observed after hypophysectomy was prevented by the presence of two pituitary autografts. Testosterone and LH-levels were non-detectable in the operated male rats. These data show that progesterone secretion by the corpora lutea is always associated with the presence of LH-receptors, regardless whether serum LH-levels are detectable or not. Moreover it appears that prolactin maintains or even increases the amount of LH-receptors in hypophysectomized male and female rats.
The influence of LH on testosterone secretion by testes from 25–30-day-old guinea pig fetuses cultured in vitro was investigated. Testosterone secretion by testes from 30-day-old fetuses could be stimulated by LH during the first 24 h in organ culture. Testosterone secretion by testes from 25–29-day-old fetuses could not be stimulated by LH during 5 days in organ culture. Development of testosterone and androstenedione synthesis by testes from fetuses of 25 days was observed during 5 days in organ culture. A stimulation of testosterone and androstenedione production by LH at that fetal age, however, could not be measured. Testosterone synthesis by fetal guinea pig testes explanted at 25 days could be stimulated by LH when they were precultured for 6 days. Similarly [125I]-hCG binding by gonads from fetuses of 25 days could be detected only after organ culture of these gonads for at least 6 days. These results indicate that in early guinea pig fetuses development of testosterone synthesis precedes the development of LH responsiveness.
Abstract. Luteinized ovaries of rats hypophysectomized shortly after ovulation 25–80 days previously secrete considerable amounts of 20α-dihydroprogesterone (20α-hydroxy-4-pregnen-3-one, 20α-OHP) into the blood-stream. The serum concentration of 20α-OHP in these hypophysectomized animals is almost similar to that of progesterone in intact pseudopregnant rats on day 7 of pseudopregnancy, in spite of the absence of demonstrable amounts of prolactin. Isolated corpora lutea of the last generation and the remainder of the ovarian tissue both contained 20α-OHP. Six months after hypophysectomy no detectable amount of 20α-OHP was found in the serum. Androgenized rats, devoid of corpora lutea, did not produce 20α-OHP after hypophysectomy. These data show that pituitary hormones are not required for the prolonged synthesis and secretion of 20α-OHP by the luteinized ovary.
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