Distribution and Regulation by Oestrogen of Fully Processed and Variant Transcripts of Gonadotropin Releasing Hormone I and Gonadotropin Releasing Hormone Receptor mRNAs in the Male Chicken

Abstract

AbstractThe aim of this study was to increase understanding of the occurrence and regulation of chicken gonadotropin releasing hormone I (cGnRH I) and chicken gonadotropin releasing hormone receptor (cGnRH‐R) mRNA variants in the hypothalamic‐pituitary‐testicular axis (HPTA). The study was carried out in the cockerel. Fully processed cGnRH I mRNA (cGnRH Ia) and a variant transcript (cGnRH Ib) with a retained intron 1 were observed in the preoptic/anterior hypothalamus (POA), the basal hypothalamus, anterior pituitary gland, and testes. Fully processed cGnRH‐R mRNA (cGnRH‐Ra) and a variant transcript (cGnRH‐Rb) with a deletion were detected in the same tissues. In juvenile cockerels, concentrations of cGnRH Ia and b in the POA increased after castration, and this was prevented by oestrogen treatment. In the anterior pituitary gland, the concentration of cGnRH‐Ra increased after castration and this was reversed by oestrogen treatment. In intact adult cockerels, oestrogen treatment depressed plasma luteinizing hormone but did not affect concentrations of cGnRH I and cGnRH‐R mRNAs in the POA, basal hypothalamus, and anterior pituitary gland, suggesting that locally produced oestrogen, by aromatization, may exert maximal suppression on cGnRH I and GnRH‐R mRNAs. In intact adult cockerels, the concentrations of cGnRH Ia and b in the testis, but not cGnRH‐Ra and b, were depressed by oestrogen treatment. It was concluded that fully processed and variant cGnRH I and cGnRH‐R mRNAs occur in all components of the HPTA. Oestrogen appears to play a role in the regulation of cGnRH Ia and b in the POA and testes, and of cGnRH‐Ra in the POA and anterior pituitary gland.