Detection of folliculostatin: a sensitive and specific bioassay using the female rat.

To establish a sensitive and specific bioassay for the FSH-suppressing activity present in porcine follicular fluid (pFF), we examined the latency of pFF action when injected IV in the acutely ovariectomized (ovax) metestrous rat. By 2h post injection (5.5h after ovax), FSH was suppressed significantly in pFF vs. porcine serum-injected controls. LH was unaltered. In an experiment establishing a dose-response curve for pFF 4.5h after injection, 1.77 mg of pFF protein significantly suppressed FSH. The index of precision (-0.2188) and precision of slope (1.088) were well within acceptable limits for bioassays. We conclude that the ovax metestrous rat, injected 3.5h after surgery and sacrificed at 4.5 or 5.5h, is a sensitive and specific bioassay for folliculostatin.

Effect of neonatal treatment with the sex-opposite steroid on gonadotropin responsiveness in rats.

This study was performed to determine if two sex differences in gonadotropin responses to negative feedback, the acute postcastration rise and the effect of follicular fluid (FF) in the acute castrate, could be reversed by neonatal treatment with sex-opposite steroids. Female rats that received testosterone propionate (TP-females) and male rats that received estradiol benzoate (EB-males) neonatally were studied as adults. EB-males showed an LH response to gonadectomy which was much less than control males, and did not differ from control females, which could suggest the hypothesis that neonatal estrogen 'feminizes' the male response to gonadectomy. However, as the postgonadectomy response in both LH and FSH was depressed in both TP-females and EB-males in comparison to their respective matched sex controls, neonatal steroid treatment appears simply to impair hypothalamic-pituitary function. This is not a result of decreased pituitary responsiveness to GnRH in TP-females and EB-males. On the other hand, neonatal steroid treatment does not change the sex-specific response to imposition of peptide negative feedback (i.e., FF administration). In control and TP-females, FF significantly suppressed serum FSH levels, both in intact animals and 9 h after gonadectomy. In both control and EB-males, FF suppressed FSH in intact animals, but failed to do so in acute castrates. Thus, neonatal steroid treatment does not reverse the sex differences in gonadal-gonadotropin interrelations, but rather causes an impairment in the acute recognition of loss of negative feedback at the hypothalamic level.

Differential suppression of follicle-stimulating hormone and luteinizing hormone secretion in vivo by a gonadotropin-releasing hormone antagonist.

Because of some indication that FSH secretion is less dependent than LH secretion on GnRH in vivo, we performed experiments to examine the effects of a GnRH antagonist (antag) on LH and FSH secretion. We first showed that pituitary cells superfused with GnRH showed a similar pattern of suppressed secretion of both LH and FSH in response to addition of antag. In contrast, antag administration to ovariectomized rats had differing effects on LH and FSH secretion. Serum LH was suppressed in a dose-dependent fashion by 2 h (20-50% of control values). Recovery from the lower doses of antag was seen by 12 h, but the two highest doses maintained serum LH levels at 10% of control values for 72 h. In contrast, the effect on serum FSH was not manifested until 12 h. FSH was maximally decreased only to 40-60% of control values. The two highest doses maintained this effect for 72 h. These results reinforce previous suggestions that FSH secretion in vivo may occur independently of acute changes in GnRH secretion, and may have an GnRH-independent component.

Differential suppression of FSH and LH secretion by follicular fluid in the presence or absence of GnRH.

The differential role of porcine follicular fluid (pFF) in regulating follicle-stimulating hormone (FSH) and luteinizing hormone (LH) release in vivo in situations of different gonadotropin releasing hormone (GnRH) backgrounds was studied. In experiment 1, 2-week ovariectomized rats injected intravenously with 4, 16 or 64 mg of protein from pFF, showed a dose-dependent suppression of FSH over time, with a maximal suppression to 40% of control values by 10 h. LH levels were slightly, but significantly, elevated by the two lower doses, but not by the highest dose of pFF. In experiment 2, 64 mg pFF was superimposed (i.v. injection) in ovariectomized rats injected subcutaneously with a high dose of GnRH antagonist (500 micrograms) 24 h earlier. The pFF suppressed FSH 35% below the level achieved in the absence of GnRH stimulation, with no effect on LH. In experiment 3, the rise in FSH secretion in acutely ovariectomized rats was shown to be inhibited by 8 or 32 mg pFF administered intravenously 3.5 h after surgery. Injection of GnRH (250 or 1,000 ng) 4.5 h after pFF could not overcome the inhibitory action of pFF on FSH, although non-pFF-treated controls responded in a dose-dependent fashion to GnRH stimulation. The expected LH response to GnRH was not affected by pFF, except in the group receiving 1,000 ng GnRH and 8 mg pFF. In these rats, LH was enhanced in one trial, but suppressed in a replicate trial, illustrating the inconsistent effects of pFF on LH under conditions of high GnRH stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal endocrine dysfunction resulting from prenatal exposure to carbofuran, diazinon or chlordane.

Prenatal exposure to pesticides of three different classes initiated persistent postnatal endocrine dysfunction. Adrenal function and hepatic metabolism of corticosterone were studied in adult hybrid mice exposed during development to either an organophosphate (Diazinon), a carbamate (Carbofuran), or an organochlorine (Chlordane). Animals were exposed to relatively low levels of the toxins in utero and neonatally via the mothers' milk. Exposure to lower doses of the anticholinesterase compounds, Diazinon or Carbofuran, resulted in impairment of hepatic metabolism of corticosterone in vitro due to a loss in reductive capacity per unit liver weight. Plasma levels of corticosterone were also elevated in these animals, but without a concomitant increase in adrenal steroidogenesis in vitro. The effects of exposure to Chlordane were more complex. In male animals, exposure to lower doses of chlordane resulted in an increase in plasma corticosterone levels without an apparent increase in hepatic metabolism of corticosterone or adrenal steroidogenesis. In contrast, side-chain metabolism of corticosterone was decreased in female mice exposed to Chlordane. Similar effects on pituitary-adrenal function were not evident for the offspring of mice exposed to higher doses of the toxins. Possible mechanisms for this non-linear dose-response are discussed.

Postnatal endocrine dysfunction induced by prenatal methylmercury or cadmium exposure in mice.

The subtle and delayed effects of two heavy metals, cadmium and mercury, on the pituitary-adrenal axis of mice were examined. Exeprimental animals were exposed to the toxins both in utero and neonatally via treated mothers' milk. Plasma levels of corticosterone, adrenal production of corticosterone in vitro, and the capacity of the liver to metabolize corticosterone in vitro were studied in these animals as adults. Exposure to methylmercury resulted in diminished hepatic metabolism of corticosterone in vitro due to a loss of liver mass. Adrenal function and plasma levels of corticosterone were unaffected by treatment. Cadmium-exposed animals examined at 277 days of age showed no significant differences when compared to untreated controls. However, when studied at 460-480 days of age, a sex difference in the response to cadmium exposure was noted. In males, the major effect was enhancement of hepatic reductive capacity, while in females, adrenal secretory capacity was enhanced. Possible mechanisms of action and consequences of these effects are discussed.