GONADOTROPIN-RELEASING-HORMONE RECEPTOR GENE-EXPRESSION IN RAT ANTERIOR-PITUITARY

Gonadotropin-releasing hormone (GnRH) effects on the lactotroph functi on have been widely studied, but they probably result from paracrine i nteractions. No visual data about GnRH receptor in the pituitary are a vailable. In order to identify the GnRH target cells in the pituitary of adult rats, the cellular distribution of rat Gn RH receptor mRNA wa s investigated by electron microscopy, using in situ hybridization on ultrathin pituitary frozen sections. In situ hybridization was perform ed using a digoxigenin-labeled oligonucleotide probe revealed by an in direct immunogold reaction. Gonadotropin-releasing hormone receptor mR NA was found in the cytoplasmic matrix, apposed to the endoplasmic ret iculum and the nucleus of the gonadotrophs, which were identified by t heir ultrastructural characteristics, and by the presence of luteinizi ng hormone (LH) immunoreactivity. It was also found in the lactotrophs , which were revealed by the immunocytological detection of prolactin. No GnRH receptor mRNA was detected in corticotrophs, somatotrophs, th yrotrophs or hepatocytes. This result, without excluding paracrine eff ects, clearly showed that in addition to the gonadotrophs, the lactoto trophs are likely to be direct target cells for the hypothalamic GnRH.