Expression of the putative gonadotropin-inhibitory hormone receptor, NPFFR1, in the anterior pituitary gland of the gilt is affected by age and sexual maturation

Abstract Text: Gonadotropin-inhibitory hormone (GnIH) purportedly suppresses secretion of luteinizing hormone (LH) by acting through a G-protein coupled receptor (NPFFR1) in the anterior pituitary gland and hypothalamus. The objective of these studies was to determine if expression of mRNA for NPFFR1 in the reproductive neurosecretory axis of gilts differed with age or sexual maturation. In Exp. 1, the anterior pituitary gland was collected from gilts at 24 (weaning), 60, 100, and 140 d of age (n = 14 to 16 per age). In Exp. 2, the anterior pituitary gland and medial basal hypothalamus were collected from gilts at 240 d of age. Gilts were classified (n = 12 to 14 per classification) as prepubertal, peripubertal, or cyclic (midluteal phase) based on estrus records and ovarian morphology at slaughter. Relative abundance of LHβ, FSHβ, CGA, GnRHR1, and NPFFR1 mRNA in pituitary glands from Exp. 1 and 2 and NPFFR1, GnRH1, NPY, POMC, and RFRP in hypothalami from Exp. 2 was measured with qPCR. Data were analyzed by ANOVA with age or reproductive classification as fixed effects. In Exp. 1, age did not affect expression of GnRHR1 or CGA. Expression of FSHβ at weaning was not different from 60 d of age but was greater (P < 0.05) than expression at 100 and 140 d of age. Compared to weaning, expression of LHβ was less (P < 0.05) at 60 d of age and greater (P < 0.05) at 100 d of age, but not different at 140 d of age. Pituitary expression of NPFFR1 was greater (P < 0.05) at 100 d of age compared with all other ages. In Exp. 2, prepubertal gilts had less pituitary expression of LHβ (P < 0.02) and greater pituitary expression of FSHβ (P < 0.04), CGA (P < 0.001), GnRHR1 (P < 0.01) and NPFFR1 (P < 0.001) than cyclic gilts. Expression of LHβ and GnRHR1 was intermediate in peripubertal gilts. Expression of FSHβ, CGA, and NPFFR1 in the pituitary did not differ between peripubertal and cyclic gilts. Expression of NPFFR1 in the hypothalamus of peripubertal gilts was less (P< 0.05) than in cyclic gilts. Reproductive classification did not affect hypothalamic expression of GnRH1, NPY, POMC, or RFRP. Increased expression of NPFFR1 in prepubertal gilts indicates an increased sensitivity to GnIH inhibition of LH secretion. Support: NIFA AFRI 2011-67015. USDA is an equal opportunity provider and employer.

Keywords: gene expression, pig, pubertal development,