Expression of ghrelin receptor, GHSR-1a, and its functional role in the porcine ovarian follicles

Recently, we reported stimulatory effect of ghrelin alone and in combination with growth hormone (GH) on estradiol secretion, aromatase activity in parallel with inhibitory effect on cell apoptosis. The aim of this study was to analyze the expression of the functional ghrelin receptor (GHS-R type 1a) and the effect of GH on GHSR-1a expression in cultured whole porcine follicles. Using RT-PCR and Western Blots, we demonstrated the presence of GHSR-1a in prepubertal pig ovary and found no influence of GH on either GHSR-1a protein levels or mRNA expression. Additionally, to show if, noted previously by us action of ghrelin on ovarian follicular function is dependent of its binding to GHSR-1a, we used an antagonist of the ghrelin receptor, (d-Lys-3)-GHRP-6. In cultures treated together ghrelin and (d-Lys-3)-GHRP-6, estradiol secretion, aromatase activity and cell proliferation returned to control levels. Inhibitory action on caspase-3 activity was not reversed by a selective antagonist of GHSR-1a. In conclusion, results of the present data clearly showed: (1) the presence of GHSR-1a in prepubertal pig ovary and found no influence of GH on GHSR-1a protein levels and mRNA expression, and (2) ghrelin effect on estradiol secretion, aromatase activity and cell proliferation dependent of its binding to GHSR-1a, while the effect on cellular apoptosis was independent of its binding to GHSR-1a.