Regulation of gonadotropin releasing hormone receptor mRNA expression in cultured rat granulosa cells

The homologous regulation of pituitary Gonadotropin Releasing Hormone Receptor (GnRH-R) mRNA expression by GnRH has been well demonstrated. However, the regulation of the ovarian GnRH-R is poorly understood. The present study was performed to demonstrate the presence of GnRH transcripts in addition to GnRH-R mRNA and the regulation of GnRH-R mRNA expression in the granulosa cells isolated from small antral follicles. The GnRH and GnRH-R mRNA levels were determined by a competitive reverse transcription-polymerase chain reaction (RT-PCR). The granulosa cells were obtained from immature rats implanted with diethylstilbestrol for 3 days. When GnRH transcript expression was examined in isolated granulosa cells by RT-PCR, the PCR products showed two bands. The larger band contained intronic sequences and the smaller band was a fully processed GnRH gene transcript identical to hypothalamic GnRH. This suggests that authentic GnRH gene transcripts are expressed in ovarian granulosa cells and may act on the granulosa cells in a paracrine or autocrine manner. Since GnRH action in the granulosa cells is mediated by specific GnRH-R, it is of interest to examine whether GnRH-R is synthesized in the granulosa cells. When the granulosa cells were cultured in media only, GnRH-R mRNA levels increased abruptly within 3 h and gradually decreased thereafter during the 24 h culture period. However, GnRH itself did not alter the GnRH-R mRNA expression levels in cultured granulosa cells. Interestingly, treatment with FSH decreased the GnRH-R mRNA levels in a dose-dependent manner. A time-course analysis revealed that the GnRH-R mRNA levels were significantly lower up to 9 h after FSH treatment, and returned to the basal level between 12 h-24 h. Activation of adenylate cyclase with forskolin also decreased the GnRH-R mRNA levels. It is therefore concluded that in the granulosa cells of the small antral follicles GnRH-R mRNA expression was not homologously regulated by GnRH, while FSH may negatively regulate GnRH-R mRNA expression in the granulosa cells possibly through a cAMP-protein kinase A pathway.

Changes in Fat Tissue and Growth Hormone Receptor mRNA after Growth Hormone Therapy

PURPOSE: Growth hormone(GH) is a powerful inhibitor of lipoprotein lipase and is known to decrease fat cell mass. The lipolytic effect has more pronounced influence on visceral fat than subcutaneous fat. The effects of GH therapy on GH receptor in fat tissue are not clear. We investigated the changes in fat tissue and GH receptor mRNA in adipose tissue with GH therapy. METHODS: Eight children with growth hormone deficiency(GHD) and 9 children with Prader-Willi syndrome(PWS) were studied. The children were treated with 0.6U/kg/week GH for 6 months. We compared fat distribution on CT scan before and after GH therapy. Abdominal fat biopsy was done in 6 children with GHD, 3 children with PWS and 3 controls before and after GH therapy. GH receptor expression by reverse transcription PCR was examined. RESULTS: In children with GHD, total, subcutaneous and visceral fat were decreased after GH therapy(P>0.05), but thigh muscle mass was increased from 6,165 to 7,689(P<0.05). In chidren with PWS, visceral fat was decreased from 7,613 to 5,022 in abdominal CT(P<0.05) and V/S ratio(visceral fat/subcutaneous fat) was decreased also from 0.37 to 0.23(P<0.05). The thigh muscle mass was increased from 6,358 to 7,175. The expressions of GH receptor mRNA were reduced in children with GHD and PWS. But it was not significant in children with PWS. CONCLUSION: In children with PWS, fat mass was reduced and muscle mass was increased after GH therapy. In children with GHD, muscle mass was increased significantly and fat mass was decreased insignificantly. We observed down regulation of GH receptor of adipose tissue in patients with GHD after GH therapy.