Effect of corticotropin releasing hormone and corticotropin releasing hormone antagonist on biosynthesis of gonadotropin relasing hormone and gonadotropin relasing hormone receptor in the hypothalamic-pituitary unit of follicular-phase ewes and contribution of kisspeptin.

Abstract

This study aimed to determine the mechanisms governing Gonadotropin releasing hormone (GnRH) biosynthesis and luteinising hormone (LH) secretion in follicular-phase sheep after infusion of corticotropin releasing hormone (CRH) and/or CRH antagonist corticotropin releasing hormone nist (CRH-A) into the third cerebral ventricle. The study included two experimental approaches: first, we investigated the effect of CRH or CRH-A (α-helical CRH 9-41) on GnRH and GnRH receptor (GnRHR) biosynthesis in the preoptic area (POA), anterior (AH) and ventromedial hypothalamus (VMH), stalk/median eminence (SME), and on GnRHR in the anterior pituitary (AP) using an enzyme-linked immunosorbent assay (ELISA); second, we used real-time PCR to analyse the influence of CRH and CRH-A on the levels of kisspeptin (Kiss1) mRNA in POA and VMH including arcuate nucleus (VMH/ARC), and on Kiss1 receptor (Kiss1r) mRNA abundance in POA-hypothalamic structures. These analyses were supplemented by radioimmunoassay (RIA) and ELISA methods for measurement of LH and cortisol levels in the blood, respectively. Our results show that administration of CRH significantly decreased GnRH biosynthesis in the POA/hypothalamus. CRH also decreased GnRHR abundance in the hypothalamus and in the AP, but increased it in the POA. Furthermore, administration of CRH decreased plasma LH concentration and levels of Kiss1 mRNA in the POA and VMH/ARC as well as Kiss1r mRNA in these structures and in the SME. Significant increase in plasma cortisol concentration in the group treated with CRH was also observed. For CRH-A, all analysed effects were opposite to those induced by CRH. The study demonstrates that intracerebroventricular (i.c.v.) infusion of both CRH and CRH-A affects the GnRH/GnRHR biosynthesis and LH secretion in follicular-phase sheep conceivably via either central and peripheral mechanisms including Kiss1 neurons activity and cortisol signals. It has also been suggested that CRH and CRH-A infusion probably had effects directly at the AP.