Effects of a gonadotrophin-releasing hormone antagonist on gonadotrophin secretion and gonadal development in neonatal pigs

Abstract

Summary. Male GnRH*HOAc; 1 mg/kg body weight) at 14 days of age. The GnRH antagonist caused LH to decline (P < 0\m=.\01) from 1\m=.\7 ng/ml at 0 h to <0\m=.\5 ng/ml during 4\p=n-\32 h in males and females. Concentrations of FSH in gilts declined slowly from 75 \ m=+-\ 8 to 56 \ m=+-\ 5 ng/ ml (P < 0\m=.\05) at 32 h. In males FSH was low (5\m=.\7 \m=+-\0\m=.\5 ng/ml) at 0 h and did not change significantly.To observe the effect of long-term treatment with GnRH antagonist, 10 male and 10 female pigs, 3 days of age, were treated with saline or 1 mg GnRH antagonist per kg body weight every 36 h for 21 days. Concentrations of LH were reduced (P < 0\m=.\01) to 0\ m=. \ 2\ p=n-\ 0\ m=. \ 4 ng/ml throughout the experimental period in male and female piglets treated with GnRH antagonist. Plasma FSH increased in control females, but remained suppressed (P < 0\m=.\001) in females treated with GnRH antagonist. Treatment with the GnRH antagonist suppressed FSH levels in males on Days 8 and 16 (P < 0\m=.\05), not on Day 24. Treatment of females with the GnRH antagonist did not influence (P > 0\m=.\10)oestradiol-17\g=b\ concentrations. Administration of GnRH antagonist to males suppressed testosterone and oestradiol-17\g=b\ values (P < 0\m=.\01) and reduced testicular weight (P < 0\m=.\01). Concentration of LH/hCG receptors in testes of boars treated with GnRH antagonist was lower (P < 0\m=.\10) than in controls, but concentration of FSH receptors was not affected. Basal and potassium-stimulated release of GnRH from the stalk median eminence and medial basal hypothalamus in vitro did not differ between treatment groups. The amount of residual GnRH in hypothalamic tissue was not different in control gilts and in gilts receiving the GnRH antagonist, but it was lower (P < 0\m=.\05) in boars treated with GnRH antagonist than in control boars.

Secretion of Gonadotropins and Estimated Releasable Pools of Gonadotropin-Releasing Hormone and Gonadotropins during Establishment of Suckling-Induced Inhibition of Gonadotropin Secretion in the Sow

“…GnRH secreted into the incubation medium and GnRH content in POA, MBH, and SME were determined by a single-antibody RIA modified slightly [8] from that described by Ziecik et al [21]. Synthetic GnRH (acetate salt; Sigma) was radioiodinated by the iodogen method [22], and the labeled hormone was separated from free iodine by anionexchange chromatography [23].…”

Effects of gonadotrophin deprivation on follicular growth in gilts

“…Two models were used, namely hypophysectomy and GnRH-antagonist administration. To our knowledge, with the exception of a study using GnRH antagonist in neonatal pigs (Ziecik et al, 1989) hypophysectomy (n = 5), GnRH antagonist (n = 5), and control (n = 6). The GnRH antagonist had the following structure (Deghenghi et al, 1993): Ac-D-Nal, D-cpa, D Pal, Ser, Tyr, D-Hci, Leu, Lys-(iPr), Pro, D-Ala-NH 2 -On the following day, gilts from the GnRH antagonist and control groups were fitted with an indwelling Silastic R (Dow Corning, Midland, MI) catheter that was inserted into 1 jugular vein under general anaesthesia as described by Camous et al (1985).…”

Contribution of Chicken GnRH-II and Lamprey GnRH-III on Gonadotropin Secretion

“…doses of cetrorelix decreased gonadotropin secretion in intact and castrated boars and gilts Zanella et al, 2000;Ziecik et al, 1989). Administration of low doses (5 µg/kg of body weight; BW) of cetrorelix resulted in a decline of LH but had no effect on FSH concentrations, while doses of 10 µg/kg BW of cetrorelix were sufficient to inhibit FSH secretion Zanella et al, 2000).…”

“…Administration of low doses (5 µg/kg of body weight; BW) of cetrorelix resulted in a decline of LH but had no effect on FSH concentrations, while doses of 10 µg/kg BW of cetrorelix were sufficient to inhibit FSH secretion Zanella et al, 2000). Larger doses (20 µg, 50 µg, and 1 mg/kg BW) of cetrorelix also resulted in a significant decrease in LH concentrations with varied responses in FSH secretion (Moran et al, 2002;Wise et al, 2000;Ziecik et al, 1989). The lack of a consistent reduction of FSH secretion in pigs treated with the type I GnRHR antagonist may be associated with the presence of two GnRHs and two GnRH receptors, together with the differences in their signaling in swine species.…”