Changes on corpus luteum structure and progesterone synthesis pathway after hCG or GnRH treatment during the early luteal phase in sheep

Abstract

This study investigated the effect of hCG or GnRH on structural changes of the corpora lutea (CL)and the regulation of the expression of steroidogenic enzymes involved in P4 secretion in postovulatory (po-CL) and accessory CL (acc-CL). Sixty-four ewes were assigned to three groupsreceiving: 300 IU of hCG (hCG) or 4 µg Buserelin (GnRH) or 1 mL of saline solution (Control) onDay (d) 4 post artificial insemination (FTAI). Laparoscopic ovarian were performed on d 4, 14and, 21 post-FTAI to determine the numbers of CL. Blood samples were collected for serum LHand P4 analysis. On d 14 post-FTAI, both CL were removed from the ovary to determine largeluteal cell (LLC) number and to evaluate the expression of steroidogenic enzymes (HSD3B1,STAR, CYP11A1). Only hCG and GnRH treated ewes generated acc-CL. The LLC in both po- andacc-CL were significantly greater in the hCG group compared to GnRH and Control groups (P<0.05). Overall, hCG group showed the greatest immunodetection of HSD3B1and STAR in bothpo- and acc-CL (P<0.05). rnRNA expression of HSD3B1, STAR and CYP11A1 in the acc-CL tendedto be greater in hCG group than in GnRH group (P<0.1). The LH concentration was increased inGnRH group (P<0.05) and P4 concentration was greater in hCG group compared to the othergroups (P<0.05). In conclusion, administration of hCG has a notably impact on acc-CL development and the expression of steroidogenic enzymes compared to GnRH treatment in ewes. Thisleads to elevated P4 concentration and improved luteal function.