Central Injection of Substance P Antagonizes the RF Amide-Related Peptide-3 Impacts on Hypothalamic KISS-1 and GnRH Gene Expressions in Male Wistar Rats

Abstract

Introduction: Gonadotropin-inhibitory hormone (GnIH) and its mammalian orthologue RF amide-related peptide (RFRP) are known to inhibit the secretion of gonadotropins. In addition, substance P (SP), a member of tachykinin’s family, can increase the firing rate of kisspeptin/ neurokinin B/dynorphin (KNDy) neurons and provoke the secretion of gonadotropins. In this experimental study, we investigated the effects of co-administration of RFRP-3 and SP on the expression of KISS-1 and GnRH genes, as gonadotropin regulator genes, in male rats. Methods: Forty-two mature Wistar rats were randomly allocated into 7 groups (n=6 in each group). Animals in each group intracerebroventricularly received either saline+DMSO, SP (1nmol), RFRP-3 (5 nmol), SP (1nmol) + RFRP-3 (5 nmol), SP (1 nmol) + RF9 (RFRP-3 receptor antagonist, 10 nmol), SP (1 nmol) + P234 (kisspeptin receptor antagonist, 1 nmol) + RFRP-3 (5 nmol), or SP (1 nmol) + CP-96,345 (SP receptor antagonist, 5 nmol) + RFRP-3 (5 nmol). Two hours after injections, hypothalamic samples were collected to evaluate the expression of target genes by real-time PCR. Results: Injections in SP and SP + RF9 groups increased the expression of both GnRH and KISS-1 genes (P<0.05). Injections in RFRP-3 and SP + RFRP-3 + CP-96,345 groups significantly decreased the expression of GnRH and KISS-1 genes (P<0.05). However, injections of SP + RFRP-3 and SP + RFRP-3 + P234 did not significantly change the expression of GnRH and KISS1 genes. Conclusion: The results of our study indicated that SP antagonized the effects of RFRP-3 in the expression of hypothalamic KISS-1 and GnRH genes.

Keywords

• RF amid-related peptid-3
• Substance P
• GnRH
• KISS-1
• Rat