Absence of an Estradiol-Induced Surge of Luteinizing Hormone in Pigs Receiving Unvarying Pulsatile Gonadotropin-Releasing Hormone Stimulation*

Abstract

The goal of this study was to pharmacologically block central nervous system (CNS) input to gonadotropes in mature ovariectomized gilts to determine the direct actions of estradiol (E2) on pituitary LH release when given at a dose sufficient to elicit a gonadotropin surge. Feeding AIMAX [N-methyl-N'-(1-methyl-2-propenyl)1,2-hydrazinedicarbothioamide; 125 mg/day] for 7 days reduced serum LH concentrations from 1.25 +/- 0.13 (mean +/- SE) to less than 0.18 ng/ml, abolished LH pulses, but did not compromise LH release in response to exogenous GnRH. Serum FSH concentrations were reduced by 27%, whereas serum concentrations of PRL, GH, thyroid hormones and cortisol were not affected after 7 days of AIMAX treatment. Behavior was not altered, aside from a slightly reduced appetite. The LH surge that peaked 48-80 h after injecting E2 benzoate (E2B) into control gilts was blocked in five of eight gilts given AIMAX. Giving GnRH pulses (1 microgram every 45 min) to AIMAX-treated gilts restored mean serum LH concentrations as well as the frequency and amplitude of LH pulses to those of untreated ovariectomized gilts. E2B suppressed the LH response to these GnRH pulses by 88% at 12 h, whereas from 24-96 h after E2B treatment, the LH response to GnRH and mean serum concentrations of LH were again similar to those of controls not given estradiol. These data indicate that induction of the gonadotropin surge by E2 in the gilt requires CNS input. The action of E2 on the pituitary in the presence of unvarying GnRH pulsation may, however, be limited to an early transient inhibition of responsiveness to GnRH, with no subsequent direct stimulation during the period of the surge.

Central and peripheral administration of kisspeptin activates gonadotropin but not somatotropin secretion in prepubertal gilts

“…Serum was separated by centrifugation and stored at K20 8C for subsequent analysis of LH (Kesner et al 1987) and FSH (Trout et al 1992) by RIA. The reference standard for LH (AFP-10506A) and FSH (AFP-10640B) was provided by Dr A F Parlow, Scientific Director of the NIH, NIDDK, National Hormone and Peptide Program.…”

The role of neuropeptide Y and interaction with leptin in regulating feed intake and luteinizing hormone and growth hormone secretion in the pig

“…Serum samples were assayed for GH (Barb et al 1991) and LH (Kesner et al 1987) as previously described. Sensitivity of the assays was 0.4 ng/ml and 0.15 ng/ml for GH and LH respectively.…”

The role of RFamide-related peptide 3 (RFRP3) in regulation of the neuroendocrine reproductive and growth axes of the boar

“…Plasma was harvested (2,000 × g for 20 min at 4 • C) and stored at −20 • C. Concentrations of LH and GH in plasma were determined by RIA as described previously (Kesner et al, 1987;Lents et al, 2008). The reference standards for LH (AFP-10506A) and GH (AFP-10864B) were provided by Dr. A.F.…”