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

RFamide-related peptide 3 (RFRP3) has been implicated in regulating reproduction and growth. This regulation appears to be dependent upon sex, species, physiological status, and developmental stage. The objective of the present study was to evaluate the effects of RFRP3 on circulating concentrations of luteinizing hormone (LH) and growth hormone (GH) in mature boars. The hypothesis was RFRP3 would reduce circulating concentrations of LH and increase concentrations of GH. Meishan boars (716.6 ± 2.8 days of age; 125.0 ± 12.4 kg BW) were randomly assigned to treatment: saline (n = 4) or RFRP3 (8.5 mg; n = 5). Plasma was collected at 15-min intervals during 3 periods: pre-treatment, treatment, and post-treatment. During the treatment period, saline or RFRP3 were administered at 15-min intervals. Treatment was administered as a loading dose of 5 mg RFRP3, followed by seven repeated injections of 0.5 mg RFRP3. Pulsatile secretion of LH and GH were not affected by saline treatment. Mean concentrations of LH in RFRP3-treated boars were greater (P < 0.01) in the pre-treatment period than in the treatment and post-treatment periods; however, the individual response to RFRP3 challenge was varied. RFRP3 suppressed (P < 0.05) mean concentrations of GH during the treatment period. It is concluded that RFRP3 can act to suppress LH secretion in some boars, but the minimal and varied response between animals does not strongly support the idea that RFRP3 is a potent hypohysiotropic hormone in the pig. Results indicate that RFRP3 may function in regulating the growth axis of swine.