Ghrelin, a 28 amino acid peptide, was recently isolated from the stomach of rat, and was identified as the endogenous ligand for the growth hormone secretagogue receptor, GHSR. Two GHSR subtypes, generated by an alternative splicing of a single gene, have been identified: the full-length type 1a receptor and truncated type 1b. The GHS-R1a is the functionally active, signal transduction form of the receptor. Ghrelin is recognized as an important regulator of growth hormone secretion (GH), food intake and a factor which controls reproduction. In addition, ghrelin and GHSR-1a expression were detected in reproductive tissue: placenta, ovary and testis. Recent date has suggested that ghrelin may also have an effect on sex hormone secretion and cell apoptosis. The aim of the study was analyze 1). Expression of GHSR-1a in ovarian follicles and the effect of GH on GHSR-1a expression; 2). Involvement of GHSR-1a in estradiol secretion, aromatase activity and caspase -3 activity. Pig ovarian follicles (34 mm) were collected from prepubertal animals. To examined the expression of GHSR-1a and influence of GH on GHSR-1a expression we used Western Blott and RT-PCR methods. Using antagonist of ghrelin receptor (D-Lys-3)-GHRP-6 (50 ng/ml), involvement of GHSR-1a in estradiol secretion, aromatase activity and caspase-3 activity were examined. Estradiol concentration was measured using direct enzyme immunoassay. Aromatase activity was measured using fluorometric substrate and caspase-3 activity colorimetric substrate. We demonstrated presence of GHSR-1a in prepubertal pig ovary and no influence of GH on both GHSR-1a protein and mRNA expression. Moreover, our study confirmed the involvement of GHSR-1a receptor in estradiol secretion and aromatase activity but not in cells apoptosis. In conclusion, our study provides the novel evidence for the expression of the GHSR-1a in the pig ovary and suggest involvement of this receptor in the control of key ovary function.
03 - 07 May 2008
European Society of Endocrinology