Absence of androgen receptor in the growth hormone releasing hormone-containing neurones in the rat mediobasal hypothalamus

Growth hormone (GH) secretory patterns are influenced by gonadal steroids, at least in part, through modulation of hypothalamic somatostatin and GH re leasing hormone (GHRH) secretion. in the adult male rat, testosterone appea rs to stimulate somatostatin gene expression by acting directly on androgen receptors in somatostatin neurones. The mechanism by which gonadal status influences hypothalamic GHRH gene expression is less clear. Gonadectomy red uces GHRH mRNA expression in rats, and this reduction can be prevented by t he administration of testosterone or partly by a nonaromatizable androgen. While these observations suggest that androgen receptors mediate the action s of gonadal steroids on GHRH gene expression, they do not provide any info rmation about the location of the androgen receptors involved in this proce ss. To determine whether GHRH neurones themselves express androgen receptor s, we double immunolabelled hypothalamic sections from colchicine-pretreate d male rats. Although there was an overlap in the anatomical distribution o f GHRH and androgen receptor-containing cell bodies, none of the nearly 900 GHRH immunolabelled cells we examined in each mediobasal hypothalamus appe ared to contain androgen receptors. These results suggest that GHRH-express ing neurones are not direct targets for androgens and therefore the effects of testosterone on GHRH gene expression must be produced indirectly by som e other neural or endocrine intermediary process.