Possible involvement of inhibin in the interrelationship between numbers of antral follicles and peripheral FSH concentrations in female rats

Abstract

The possible dependence of peripheral concentrations of FSH on a non-steroidal, ovarian factor, was studied in adult female rats. Increases in FSH levels during the periovulatory period were not correlated with decreases of steroid concentrations, and administration of steroids did not result in a reduction of FSH levels to basal values. However, a negative correlation between FSH levels and numbers of large follicles (volume greater than or equal to 200 x 10(5) micron 3) was demonstrated, and injection of steroid-free bovine follicular fluid, which contains inhibin-like activity, suppressed FSH levels to basal values. These results suggest that an ovarian, inhibin-like factor is involved in the fast regulation of FSH concentrations in the periovulatory period, and that this inhibin-mediated control of FSH might play a role in the regulation of the number of follicles maturing in female rats.

Involvement of Inhibin in the Regulation of Follicle-Stimulating Hormone Concentrations in Prepubertal and Adult, Male and Female Rats

“…The rise in FSH after ovariectomy could only be prevented at 25 days of age by an injection of oestradiol benzoate and progesterone, although the dose used results in near-physiological levels of oestradiol at 20 days of age (Meijs-Roelofs, and in approximately physiological levels of progesterone at all ages studied ( Table 3). The ineffectiveness of steroids in suppressing levels of FSH in short-term experiments was reported earlier for the adult unilaterally ovariectomized rat (Butcher, 1977;Welschen, Dullaart & de Jong, 1978) and for the pro-oestrous rat (Welschen et al 1980). However, injection of follicular fluid could suppress FSH levels both in the unilateral ovariectomized rat and in the pro-oestrous rat (Marder et al 1977;Welschen et al 1980).…”

“…The ineffectiveness of steroids in suppressing levels of FSH in short-term experiments was reported earlier for the adult unilaterally ovariectomized rat (Butcher, 1977;Welschen, Dullaart & de Jong, 1978) and for the pro-oestrous rat (Welschen et al 1980). However, injection of follicular fluid could suppress FSH levels both in the unilateral ovariectomized rat and in the pro-oestrous rat (Marder et al 1977;Welschen et al 1980). Furthermore, in this study injection of steroid-free bFF was, at all ages tested, capable of preventing the rise of FSH after ovariectomy.…”

“…Preliminary results from this study have appeared elsewhere ; de Jong, Welschen, Hermans, Smith & van der Molen, 1979;Welschen, Hermans & de Jong, 1980).…”

“…Either 48 h or immediately after the operation, animals were given at 09.00 h an intraperitoneal injection of 500 pi bovine plasma or bFF/100 g body wt. In these experiments this dose was always used since it causes a maximal suppression of FSH levels in both prepubertal and adult, male and female rats Welschen et al 1980). Additional groups of rats received a subcutaneous injection of 100 pi oil, 100 pi oil containing 25 pg testosterone and 0005 pg oestradiol benzoate (males) or 100 pi oil containing 0-012 pg oestradiol benzoate and 0-075 mg progesterone (females)/100 g body wt at 09.00 hand 13.00 h after bilateral gonadectomy performed at 09.00 h on the same day.…”

Increase in ovulation rate after treatment of ewes with bovine follicular fluid in the luteal phase of the oestrous cycle

“…Follicular fluid from a variety of species including sheep (Cummins, O'Shea, Bindon, Lee & Findlay, 1983), cow (Chappel & Selker, 1979;de Jong & Sharpe, 1976;Hermans, Debets, van Leeuwen & de Jong, 1981;Welschen, Hermans & de Jong, 1980), pig (Marder, Channing & Schwartz, 1977;DePaolo, Hirshfield, Anderson, Barraclough & Channing, 1979;Thomas & Nikitovitch-Winer, 1984), horse (Miller, Wesson & Ginther, 1981) and man (di Zerega, Marrs, Roche, Campeau & Kling, 1983) has been shown to suppress FSH secretion when administered to both sexes of a variety of experimental animals (sheep, monkey, rodent and horse). Bovine follicular fluid has also been demonstrated to delay oestrus in ewes and cows (Miller, Critser, Rowe & Ginther, 1979;McNeilly, 1984) when given during the preovulatory period.…”