In vivo administration of a GnRH antagonist to male mice: effects on pituitary gonadotropin secretion in vitro.

The potent luteinizing hormone-releasing hormone antagonist [N-Ac-D-p-Cl-Phe1,2,D-Trp3,D-Arg6,D-Ala10]GnRH (4 mg/kg) was administered sc once or daily for 21 days to immune-deficient (nude) and normal immune-competent (NIC) male mice derived from the same genetic background. Effects of in vivo pretreatment with the antagonist on gonadotropin secretion from hemipituitary glands from both types of mice were studied in vitro in the presence or absence of synthetic GnRH. Treatment with the GnRH antagonist caused differential effects on release of FSH and LH from and amounts of FSH and LH in hemipituitary glands.

In-vitro secretion of inhibin-like activity by Sertoli cells from normal and prenatally irradiated immature rats.

The influence of in-vitro conditions on the production of inhibin by Sertoli cells from 21-day-old normal and prenatally irradiated rat testes was studied by measuring inhibin activity in culture media, using the suppression of the release of FSH from cultured rat pituitary cells. Sertoli cells secreted inhibin-like activity during at least 21 days of culture, and cells cultured at 37 degrees C produced significantly more inhibin than those cultured at 32 degrees C. The presence of fetal calf serum had no significant effect on inhibin production at 32 degrees C, while at 37 degrees C the production was decreased.

Influence of neonatal hemicastration on in-vitro secretion of inhibin, gonadotrophins and testicular steroids in male rats.

Pituitary secretion of FSH in male animals is regulated, at least partly, by a protein hormone, inhibin, which is produced by Sertoli cells in the testes. To establish at which age the role of testicular inhibin in the regulation of FSH secretion becomes apparent, groups of male rats were hemicastrated or sham-operated on day 1 of life and pituitary and testicular function were investigated in vitro at 21, 42 or 63 days of age. Testis weights were increased in hemicastrated rats at all ages studied.

Differences between the regulation of cholesterol side-chain cleavage in Leydig cells from mice and rats.

A Leydig cell culture system has been used to study the in vitro modulation by luteinizing hormone (LH) of steroidogenesis in Leydig cells isolated from mice and immature rats. Mouse Leydig cells precultured for 24 h in the presence of increasing concentrations of LH (1 ng-1 microgram/ml) showed a dose-dependent decrease of the maximal LH-stimulated testosterone production. After pretreatment with 1 microgram LH/ml, maximal LH-stimulated testosterone production.

Prolonged steroidogenesis in luteinized ovaries of hypophysectomized rats.

Luteinized ovaries of rats hypophysectomized shortly after ovulation 25-80 days previously secrete considerable amounts of 20 alpha-dihydroprogesterone (20 alpha-hydroxy-4-pregnen-3-one, 20 alpha-OHP) into the bloodstream. The serum concentration of 20 alpha-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 20 alpha-OHP.