M.sc. Graduated of Animal Physiology and Researcher of Iranian Society of physiology and

Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Corpus luteum (CL) is a small, transient endocrine gland formed following ovulation from the secretory cells of the ovarian follicles. The main secretory product of CL is progesterone, which is required for the establishment and maintenance of pregnancy and regulates various reproductive functions. Progesterone plays a key role in the regulation of the length of estrous cycle and in the implantation of the blastocysts. Additionally, progesterone serves as a negative feedback mechanism to the hypothalamus to suppress further follicular development. The inadequate progesterone production is the major cause of infertility and embryonic loss, since progesterone is essential for both endometrial growth and embryo survival. Corpus luteum is formed following ovulation, but the real stimulus for luteinization represents the preovulatory LH surge from hypophysis. Even in case when ovulation does not occur, granulosa cells will differentiate and form CL, while oocyte will be trapped within the non