Feedback Regulation of Gonadotropic Hormone Secretion in Neonatal Pigs

Abstract

The effect of castration and of administration of charcoal-treated porcine follicular fluid (pFF) containing inhibin-like activity on plasma concentration of gonadotropic hormones was studied in neonatal pigs. Plasma follicle-stimulating hormone (FSH) concentration averaged 25.1 +/- 1.5 ng/ml (mean +/- SEM) in 1-wk-old females and gradually declined to 20.2 +/- 0.7 ng/ml 6 wk later. Ovariectomy did not significantly influence plasma FSH concentration. In males, concentration averaged 8.0 +/- 0.7 ng/ml before castration but rose significantly within 2 days after castration. Injection of luteinizing hormone-releasing hormone (LHRH) did not influence plasma FSH concentrations in intact males, but did in females and in 7-wk-old males castrated at 1 wk. Plasma luteinizing hormone (LH) concentrations in 1-wk-old females (2.2 +/- 0.4 ng/ml) gradually declined and were not influenced by castration. Concentrations of plasma LH in 1-wk-old male piglets (2.8 +/- 0.7 ng/ml) were not significantly influenced by castration within 2 days but were significantly higher 6 wk later. LHRH induced a significant rise in plasma LH concentrations in all animals. Injection of pFF resulted in a decline of plasma FSH concentrations in intact and castrated males and in intact females, but did not influence plasma LH concentrations. These data demonstrate a sex-specific difference in the control of plasma FSH, but not in plasma LH concentration in the neonatal pig. Plasma FSH concentrations, but not plasma LH concentrations, are suppressed by testicular hormones in 1-wk-old piglets. Plasma FSH concentrations can be suppressed in both neonatal male and female pigs by injections of pFF.

Interrelationships of Porcine X and Y Chromosomes with Pituitary Gonadotropins and Testicular Size1

“…An increase in plasma FSH after unilateral castration on Day 1 or 10 supports previously reported negative feedback regulation of FSH secretion [41]. This differs from ineffective negative feedback regulation of LH secretion during this period [41][42][43].…”

Increased plasma follicle-stimulating hormone concentrations in prepubertal gilts from lines selected for increased number of corpora lutea.

“…tion. During early postnatal development in gilts, negative feedback regulation of FSH secretion remains inoperative (Colenbrander et al, 1987). These investigators observed similar plasma FSH concentrations in 42-dold gilts whether gilts were intact or had undergone ovariectomy 5 wk earlier.…”

“…Concentrations of FSH are high in prepubertal gilts due to ineffective negative feedback mechanisms (Colenbrander et al, 1987). As puberty approaches, plasma FSH decreases (Diekman et al, 1983;Camous et al, 1985) in association with the appearance of antral ovarian follicles (Oxender et al, 1979).…”

Naloxone Elevates Plasma Follicle Stimulating Hormone but Not Luteinizing Hormone Levels in the Immature Male Pig

“…The lack of an LH response to NAL and morphine (Trudeau et al 1988) (Colenbrander et al 1978;Trudeau et al 1988) in 4-to 5-wk-old boars is not conducive to opiodergic control of LH secretion (Bhanot and Wilkinson 1984 (Colenbrander et al 1987). In contrast, injection of GnRH in 4-to 6-wk-old male pigs stimulates release of both gonadotropins (Trudeau et al 1988 and present study We appreciated the help of Ed Maycher, Bob…”