Effect of progesterone and its 5 alpha-reduced metabolites on gonadotropin levels in estrogen-primed ovariectomized rats.

In an effort to determine whether the metabolic conversion of progestrone may be important in the feedback effects of this steroid, serum LH and FSH levels were measured after administration of progesterone, 5 alpha-dihydroprogesterone or 3 alpha-hydroxy-5 alpha-pregnan-20-one to estrogen-primed ovariectomized rats. A single injection of 2 or 4 mg progesterone, 4 mg 5 alpha-dihydroprogesterone, or 4 mg 3 alpha-hydroxy-5 alpha-pregnan-20-one 72 h (Day 3) after estrogen pretreatment induced a highly significant increase in serum LH and FSH 6 h later (1800 h). Although serum gonadotropin levels had begun to decrease 12 h after administration of the progestins, they were still significantly higher than control values and did not return to baseline levels until noon on Day 4. When either progesterone or 3 alpha-hydroxy-5 alpha-pregnan-20-one was administered at noon on Days 3 and 4, there was a significant reduction in LH levels 6 h after the second injection. In contrast, serum LH levels were slightly elevated 3 to 6 h (1500 to 1800 h) after the second injection of 5 alpha-dihydroprogesterone and did not decrease until 2100 h. There was no effect on FSH concentrations after a second injection of any of the progestins. Loss of uterine luminal fluid was observed within 24 h after a single injection of progesterone. Neither of the 5 alpha-reduced metabolites had an effect on uterine ballooning until after the second injection, and, even then, nonfluid-filled uteri were observed in only 20 to 30% of the animals. The results suggest that the conversion of progesterone to 5 alpha-dihydroprogesterone and 3 alpha-hydroxy-5 alpha-pregnan-20-one by neuroendocrine tissues may be necessary for the positive and negative feedback effects of progesterone on gonadotropin secretion. Thus, the diverse effects of progesterone may be due to progesterone per se (e.g., in the uterus) and/or its metabolites (e.g., in the hypothalamus and pituitary).

Quantitative changes in the metabolism of 20alpha-hydroxy-4-pregnen-3-one by rat hypothalamus and pituitary during proestrus.

The in vitro conversion of 20alpha-hydroxy-4-pregnen-3-one (20alpha-DHP) by medial basal hypothalamus and anterior pituitary was investigated throughout the day of proestrus in the 4-day cyclic rat. Reverse isotopic dilution analysis was utilized to quantitate the substrate remaining and three metabolic products: 20alpha-hydroxy-5alpha-pregnan-3-one, 5alpha-pregnane-3alpha,20alpha-diol and progesterone. Serum levels of 20alpha-DHP, progesterone, LH and FSH were measured by radioimmunoassay. Conversion of 20alpha-DHP to its 5alpha-reduced metabolites (20alpha-hydroxy-5alpha-pregnan-3-one and 5alpha-pregnane-3alpha,20alpha-diol) by the pituitary was constant throughout proestrus except for a significant decrease at 1600 h, near the end of the critical period. Although 5alpha-reduction of 20alpha-DHP by the hypothalamus fluctuated, it was relatively high at 1600 h and was lowest at 1400 h. Small amounts of progesterone (less than2%) were formed but there was not variation with time. The decrease in pituitary enzymic activity coincided with the time when serum levels of LH, FSH and progesterone were increasing but not with later times when the elevated serum levels were maintained. Thus, there may be endogenous regulation of 5alpha-reductase and 3alpha-hydroxysteroid dehydrogenase activity in rat pituitary and perhaps hypothalamus on the afternoon of proestrus. The regulation and subsequent effects of quantitative changes in 5alpha-reduction of 20alpha-DHP by pituitary and hypothalamus remain to be elucidated.

Effect of neuraminidase treatment on the biological activity of highly purified ovine FSH and LH in hypophysectomized immature male and female rats.

Highly purified ovine FSH and LH were treated with neuraminidase to remove sialic acid and the desialylated derivatives were examined for biological activity in hypophysectomized immature male and female rats. The male rats were hypophysectomized at 22 days of age and beginning on day 25 were injected sc twice daily for 4 days with native or neuraminidase-treated FSH (total dose, 15 or 60 mug) or LH (12 mug). The ventral prostates, seminal vesicles, and testes were then removed and weighed, and serum testosterone levels were measured by radioimmunoassay. The female rats were hypophysectomized on day 28 and beginning on day 35 were injected sc twice daily for 4 days with native or neuraminidase-treated FSH (8 mug) or saline. On the morning of day 39, the rats were given an ovulating dose of gonadotropin (8 mug native or neuraminidase-treated FSH, or 1.28 mug native or neuraminidase-treated LH) or 1.0 ml saline iv via tail vein. Twenty-four hours later ova were counted in the oviducts the ovaries were weighed, and serum levels of progesterone and 20alpha-dihydroprogesterone were determined by radioimmunoassay. Treatment of ovine LH with neuraminidase did not diminish the ability of this hormone to increase prostate and testes weights and serum testosterone levels. Desialylation also did not decrease the ability of LH to induce ovulation. Although native ovine FSH significantly increased the weights of the ventral prostate, seminal vesicles, and testes, and elevated plasma testosterone levels, the desialylated derivative was essentially inactive. Neuraminidase treatment also eliminated the ability of ovine FSH to increase ovarian weight, to induce ovulation, and to elevate serum progesterone and 20alpha-dihydroprogesterone. These results indicate that the LH-like activity of ovine FSH is an intrinsic property of the FSH molecule.