Immunoneutralization of circulating inhibin in the hypophysiotropically clamped male rhesus monkey (Macaca mulatta) results in a selective hypersecretion of follicle-stimulating hormone.

The purpose of this experiment was to examine directly whether inhibin is involved in the testicular regulation of FSH secretion in the male rhesus monkey. To this end, the pituitary-testicular axis in eight juvenile monkeys was prematurely activated by a chronic iv infusion of GnRH (0.1 microgram/min for 3 min every 3 h). After a minimum of 5 weeks of pulsatile GnRH stimulation, four animals received a brief (30-min) iv infusion of an ovine antiserum to inhibin alpha-subunit (approximately 10 ml/kg BW), and four monkeys received a comparable volume of a control ovine immune serum. The pulsatile GnRH infusion continued without interruption throughout the entire experiment. The FSH response to passive immunization against inhibin was determined by measuring concentrations of this gonadotropin in sequential plasma samples collected immediately before a GnRH infusion and for 3 h thereafter (an inter-GnRH pulse interval) on days 0.5, 1, 2, 4, 8, and 16 after injection of the immune serum. Administration of the antiserum to inhibin alpha-subunit resulted, within 2 days, in a 2- to 3-fold increase in the mean concentration and pulse amplitude of plasma FSH. The hypersecretion of FSH induced by administration of the antiserum to inhibin alpha-subunit was maintained until day 4, and then mean concentrations and mean pulse amplitudes of plasma FSH declined, reaching preantibody control levels by day 16. The time course of the antiserum-induced hypersecretion of FSH was closely correlated to changes in circulating inhibin-binding activity. Most importantly, the hypersecretion of FSH observed during the first 2 days after immunoneutralization of circulating inhibin was indistinguishable from that elicited during the initial 2 days after subsequent bilateral orchidectomy and concomitant testosterone (T) replacement. Administration of a control immune serum did not influence circulating FSH concentrations, and neither the antiserum to inhibin alpha-subunit nor the control immune serum induced changes in pituitary LH secretion and testicular T release. Since the exogenous drive to the pituitary-testicular axis of the animals was clamped in a mode that produced a pattern of pulsatile LH and T secretion comparable to that observed in adult monkeys, the present findings provide evidence for the view that inhibin plays a major role in the testicular regulation of FSH secretion during adulthood by exerting a selective inhibition on the secretion of this gonadotropin directly at the level of the anterior pituitary gland.

Concentrations of oestradiol-17 beta in plasma and milk and progesterone in plasma during the oestrus cycle and in early pregnancy in goats.

Pre-ovulatory peaks in oestradiol-17 beta concentrations were observed on days 1 or 2 and post-ovulatory peaks between days 4 and 7, both in jugular venous plasma and defatted milk, day 1 being the day of the onset of oestrus in the goats. Mean values of the magnitudes of these concentration peaks and of their timing (relative to oestrus) during the oestrus cycle did not differ significantly (P greater than 0.05) from those when the goats were mated and became pregnant. Pre-ovulatory oestradiol-17 beta peaks were invariably greater than the corresponding post-ovulatory peaks, as were peak concentrations in plasma relative to those in defatted milk collected on the same day. Mean intervals between the pre- and post-ovulatory peaks in oestradiol-17 beta concentrations were respectively 4.2 days for plasma and 4.0 days for defatted milk. Concentrations of oestradiol-17 beta in jugular venous plasma and defatted milk were strongly correlated: rank correlation coefficients for the three goats studied were 0.871, 0.668 and 0.739. It is suggested that in goats, as in cattle, ovarian follicular oestradiol-17 beta secretion approaching pre-ovulatory level is restored by 4 days after oestrus and its rapid decline after this time may be due to the inhibitory influence of the rapidly rising plasma progesterone concentration.

Circulating inhibin alpha concentrations in infant, prepubertal, and adult male rhesus monkeys (Macaca mulatta) and in juvenile males during premature initiation of puberty with pulsatile gonadotropin-releasing hormone treatment.

Circulating inhibin alpha concentrations were determined in infant, juvenile, and adult male rhesus monkeys with a RIA employing antisera to a synthetic fragment of the alpha-subunit of porcine inhibin. Binding of tracer, [DSer1,Nle5]human inhibin alpha(1-25)-Gly-125I-Tyr, to antibody was inhibited by standard, [DSer1,Nle5]human inhibin alpha(1-25)-Gly-Tyr. and by plasma from adult male monkeys in a parallel fashion. Castration in adults resulted in a 5-fold decline in the levels of immunoreactivity in plasma. Mean (+/- SE) plasma inhibin alpha concentrations in infants and adults (322.9 +/- 51.9 and 460.1 +/- 43.9 pg/ml, respectively) were significantly higher (P less than 0.05) than those in juveniles (191.3 +/- 28.3 pg/ml). Moreover, initiation of puberty in juvenile males, 13-18 months of age, with a chronic (10- to 12-week) intermittent iv infusion of GnRH (0.1 microgram/min for 3 min every 3 h) resulted in a progressive rise in circulating inhibin alpha that plateaued, after 5 weeks of pituitary stimulation, at concentrations (343.9 +/- 38.2 pg/ml) comparable to those of infants and adults and twice those observed before initiation of the pulsatile infusion of GnRH. Circulating FSH concentrations increased during the first week of GnRH stimulation from 2.7 +/- 0.1 ng/ml before treatment to 6.0 +/- 1.2 ng/ml, where they remained for the duration of the experiment. Testosterone secretion during the initiation of precocious puberty occurred in discrete episodes that were robustly correlated with GnRH-induced LH discharges. In contrast, changes in circulating inhibin alpha concentrations over the 3-h interval between GnRH pulses were unremarkable. Activation of Sertoli and Leydig cells during initiation of puberty in the juvenile males, as reflected by circulating inhibin alpha and testosterone concentrations, respectively, occurred with similar time courses. At the time of orchidectomy, 10-12 weeks after initiation of GnRH treatment, testicular tissue was prepared for histological examination. In spite of a 2-fold gain in testicular weight and in hypertrophy of Sertoli cells in association with GnRH stimulation, maturation of the germinal epithelium did not progress past prophase I spermatocytes, and the number of these latter cells was meager. These findings indicate that the testis of the infant primate, like that of the adult, secretes significant amounts of inhibin, and that the quiescent Sertoli cell of the juvenile males may be readily provoked by appropriate gonadotropin stimulation into producing inhibin. The results also fail to provide evidence for the view that changes in circulating inhibin concentrations are robustly related, in an inve

Bilateral orchidectomy and concomitant testosterone replacement in the juvenile male rhesus monkey (Macaca mulatta) receiving an invariant intravenous gonadotropin-releasing hormone (GnRH) infusion results, as in the hypothalamus lesioned GnRH-driven adult male, in a selective hypersecretion of follicle-stimulating hormone.

The purpose of this experiment was to determine whether the testes of the juvenile male rhesus monkey, receiving an invariant intermittent iv infusion of GnRH, produce a specific FSH secretion-inhibiting hormone that exerts its action directly at the level of the pituitary gland. To this end, five male rhesus monkeys between 13-18 months of age were treated with a chronic intermittent iv infusion of GnRH (0.1 microgram/min for 3 min every 3 h) for 10 weeks to elicit an adult-like pattern in the episodic activity of the pituitary-Leydig cell axis. Animals were then bilaterally orchidectomized, and on the day of castration testosterone replacement with testosterone-containing Silastic capsules that maintained circulating levels of the steroid at approximately 6 ng/ml was initiated. Sequential blood samples were collected before castration and at 4-5, 11-13, and 18-19 days thereafter. Removal of the testes resulted in a marked and selective hypersecretion of FSH, a response very similar to that observed previously in hypothalamus-lesioned GnRH-treated adult males. This finding indicates that it will be possible to substitute the juvenile male for the much larger hypothalamus-lesioned adult in future studies requiring a hypophysiotropic clamp preparation. Such a modification of this experimental model will facilitate an examination of the effects on FSH secretion of passive immunization with inhibin antisera and of administering pure inhibin peptides.

Reconciliation of the paradox that testosterone replacement prevents the postcastration hypersecretion of follicle-stimulating hormone in male rhesus monkeys (Macaca mulatta) with an intact central nervous system but not in hypothalamic-lesioned, gonadotropin-releasing hormone-replaced animals.

Testosterone (T) replacement suppresses the postcastraction hypersection of follicle-stimulating hormone (FSH) in monkeys with an intact central nervous system (CNS), but not in hypothalamic-lesioned animals in which the pituitary-testicular axis is driven by an i.v. infusion of gonadotropin-releasing hormone (GnRH). One possible explanation for this finding is that T replacement markedly reduces the frequency of pulsatile GnRH release in CNS-intact animals. Under such a state of compromised hypophysiotropic drive to the gonadotropes, removal of a specific FSH-inhibiting factor would not be expected to lead to a hypersecretion of FSH. To test this hypothesis indirectly, adult monkeys were orchidectomized and immediately implanted with T-containing Silastic capsules to maintain circulating T concentrations in the upper physiological range, thereby preventing the postcastration hypersecretion of luteinizing hormone (LH) and FSH. An intermittent i.v. infusion of GnRH, identical to that used in studies with the hypothalamic-lesioned, GnRH-replaced model (1 microgram/min for 3 min every 3 h), was initiated 1 wk after castration and T replacement; subsequently, plasma LH and FSH concentrations were determined on Days 8 and 16-18 of GnRH treatment in samples collected every 20 min for 9 h. This GnRH stimulus resulted in a striking elevation in FSH concentrations from 5.2 +/- 1.5 ng/ml (mean +/- SE) before GnRH treatment to 62.6 +/- 20.8 and 118.3 +/- 33.1 ng/ml on Days 8 and 16-18 of GnRH treatment, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Institution of combined treatment with testosterone and charcoal-extracted porcine follicular fluid immediately after orchidectomy prevents the postcastration hypersecretion of follicle-stimulating hormone in the hypothalamus-lesioned rhesus monkey (Macaca mulatta) receiving an invariant intravenous gonadotropin-releasing hormone infusion.

In the male rhesus monkey, the negative feedback regulation of gonadotropin secretion by the gonad involves a specific inhibitory action of a testicular hormone on FSH release at the level of the anterior pituitary gland. Neither circulating testosterone (T) nor estradiol appears to be able to account for the testicular inhibition of FSH in this species. The purpose of the present study was to begin to examine the role of gonadal peptides in this regard. To this end, an episodic pattern of activity in the pituitary-Leydig cell axis was restored in seven hypothalamus-lesioned male rhesus monkeys with a chronic and unchanging intermittent iv infusion of GnRH (0.1 microgram/min for 3 min every 3 h). This preparation, known as the hypophysiotropic clamp, has been described in detail previously. Charcoal-extracted porcine follicular fluid (pFF) was used as the source of gonadal peptides. In five animals, initiation of combined T replacement and pFF treatment (10-15 ml, sc, every 12 h for 8 days) maintained circulating FSH at concentrations similar to those observed before gonadectomy. Withdrawal of pFF treatment for 8 days while maintaining T replacement resulted in a progressive and dramatic rise in plasma FSH concentrations. Reinitiation of pFF treatment resulted in a return of circulating FSH concentrations toward precastration control values. Changes in LH secretion throughout the experiment were unremarkable. In an attempt to assess any nonspecific effects of porcine protein on gonadotropin secretion, the remaining two animals received charcoal-extracted pig serum instead of pFF. In these animals circulating FSH concentrations rose 7- to 8-fold during the 8 days of combined T replacement and pig serum treatment. These findings provide evidence to support the view that a testicular peptide, most probably inhibin, plays a major role in the negative feedback regulation of gonadotropin secretion in the monkey by exerting an inhibitory action on FSH secretion directly at the level of the anterior pituitary gland.