Central Substance P Attenuates RFamidrelated Peptide3 Impacts on the Serum Level of Luteinizing Hormone in Wistar Rats

Introduction: It is wellestablished that gonadotropininhibitory hormone (GnIH) and its mammalian orthologues (RFRP: RFamid related peptides) can decrease gonadotrophin secretion. Moreover, substance P (SP) is another modulator of the secretion of gonadotropins in a speciesdependent manner. This study aimed to find out the impacts of concomitant infusion of RFRP3 and SP on luteinizing hormone (LH) concentration. Methods: Fortytwo rats were arbitrarily assigned to 7 groups (n=6 per group). Animals in the experimental groups were intracerebroventricularly injected with saline +DMSO, SP, RFRP3, SP + RFRP3, SP + RF9 (RFRP3 receptor antagonist), SP + P234 (kisspeptin receptor antagonist) + RFRP3 and SP + CP96,345 (SP receptor antagonist) + RFRP3 in a final volume of 3 µL. Blood samples were collected at 30minute intervals after injections, and serum was used to measure the LH concentration by radioimmunoassay. Results: According to the results, injections led to the elevation of LH serum concentration at 30minute post injection (P lt;0.05) in the SP and SP+RF9 groups. Moreover, administration of either RFRP3 or SP + RFRP3 + SP receptor antagonist strikingly decreased the LH mean serum concentration at 30minute after injections (P lt;0.05). On the contrary, the infusion of SP+RFRP3 and SP+RFRP3+P234 caused no dramatic changes in the LH mean serum concentration. Conclusion: In general, the data showed that SP suppresses the impacts of RFRP3 on the serum levels of LH.