Ghrelin role in apoptosis and proliferation of ovine ovarian follicles and corpus luteum

It is well known that apoptosis and proliferation are the common and essential events of reproductive function, especially during the development of pregnancy. In this regard, ghrelin a novel orexigenic peptide has been identified as a modulator of apoptosis and proliferation in the ovary. Hence, the present study was designed to evaluate the role of ghrelin in ovarian tissue during the second half of ovine pregnancy. The ovary samples of 120 sheep were collected at 3, 3.5, 4, 4.5 and 5 months of pregnancy and their follicles and potent corpora lutea (CL) were dissected from the surrounding tissues. Immunohistochemical evaluation was used against proliferating cell nuclear antigen (PCNA) and anti-apoptotic protein (Bcl-2) both in ovarian follicles and potent CL. Caspase-3 activity was considered as an apoptotic index by a kinetic method. Ghrelin, estrogen and progesterone concentrations were measured in the ovarian tissue homogenates via ELISA. Immunohistochemical analysis indicated that the stage of pregnancy affects the immunolabeling cells against PCNA and Bcl-2 proteins. Immunoreactivity was observed more at 3.5 month of pregnancy for PCNA protein in tertiary follicles, and PCNA and Bcl-2 expressions were more noticeable at 3.5 and 4 months of pregnancy in potent CL (P <0.001). The caspase-3 activity in CL significantly increased during the 5th month and decreased in tertiary follicles at the 3.5 month of pregnancy (P <0.001). Ghrelin concentration increased concomitant with estradiol concentration during pregnancy and there was a close relationship between follicular estradiol and ghrelin concentration (r = 0.97, P = 0.0004). The progesterone level increased in the 3.5, 4, 4.5, and 5th month of pregnancy compared to the 3rd month for follicles, whereas the potent CL showed an elevation of progesterone concentration at the 4.5 month of pregnancy (P < 0.001). The present findings demonstrate the regulatory role of ghrelin, possibly by estradiol functions during the second half of ovine pregnancy.