GROWTH HORMONE (GH) RECEPTOR GENE EXPRESSION IN THE HYPOTHALAMUS IS INCREASED DURING PUBERTY

Abstract

The development of a pulsatile pattern of GH secretion occurs at puberty. Although the mechanisms responsible for the generation of GH pulses are unknown, a direct feedback effect of GH on the hypothalamus (via GH receptors) appears to play an important role. We tested the hypothesis that GH receptor gene expression changes over puberty by comparing GH receptor mRNA levels in the periventricular nucleus (PeN) of prepubertal (25 days) and adult (70 days) male rats. We performed in situ hybridization on coronal brain slices using a 35S-UTP-labeled cRNA probe and measured autoradiographic silver grains above GH receptor mRNA-containing cells. We observed that cellular levels of GH receptor mRNA (reported as grains/cell±SE) were significantly higher in adult compared to prepubertal animals (116±6 vs 92±4, respectively; p<0.05). The factors responsible for this pubertal increase in GH receptor message are unclear; however, mean plasma levels of GH increase during puberty and GH has been shown to increase GH receptor mRNA levels in other tissues. Therefore, we tested the hypothesis that GH regulates GH receptor gene expression in the PeN by comparing cellular levels of GH receptor mRNA among groups of control and GH-deficient rats (both dwarfs and GHRH antibody-treated). GH deficiency did not significantly alter the GH receptor mRNA levels when compared with control levels. Conclusion: An increase in GH receptor gene expression may be involved in the pubertal development of pulsatile GH secretion. This increase in GH receptor mRNA most likely occurs independent of increased mean plasma GH levels.