Expression of ghrelin and its receptor in porcine ovarian follicles collected from prepubertal and estrous cycle animals.

Ghrelin, a hormone predominantly found in the stomach, was described as a factor that controls female reproductive function. Using real time PCR and western blot, we measured gene and protein expression of ghrelin and its receptor. Enzyme-like immunoassay (ELISA) was used to measure the concentration of acylated (Ac) and unacylated (UnAc) forms of ghrelin as well as levels of estradiol (E2) in follicular fluid. For all analyses, we compared small, medium and large ovarian follicles collected from ovaries of prepubertal and estrous cycling pigs. We demonstrated that the gene expression levels of ghrelin significantly increased in ovarian follicles from cycling animals, with the maximum expression in large follicles, without any change in prepubertal. However, the protein expression of ghrelin and its concentration was increased with increasing follicle size both in prepubertal and cycling animals and it was positively correlated with E2 levels in follicular fluid. In addition, both receptor growth hormone secretagogue receptor (GHSR) and GHSR type GHSR-1a expression were significantly higher in ovarian follicles from cycling animals than prepubertal. Results of this study suggest the possibility of local synthesis of ghrelin in the ovarian follicles and point to important modulatory functions for ghrelin before puberty and during the estrous cycle.