ABSTRACT
In this work, the relationship between histological structure of corpus luteum and steroid hormones during estrous cycle of buffalo- cows was studied. Corpora lutea and blood samples were collected from slaughtered animals. The corpora lutea were prepared for a histological examination using electron microscope, while progesterone and estradiol-17 beta were estimated from serum. The results revealed a relation between fine structure of lutein cells and concentrations of progesterone during the same stage of the estrous cycle. The main change which occurred in the cytoplasm of the lutein cells was variation of the number of the secretory granules. After metestrus phase and during the diestrus one, levels of progesterone increased gradually and the cytoplasm of the lutein cells became vacuolated containing lipid droplets, electron dense granules, numerous mitochondria and SER. At estrus phase, a significant sharp decrease of progesterone and a rise of estradiol-17 beta were associated with severe changes in luteal cells of corpus albicans containing numerous lipid droplets of different sizes and empty spaces, followed by a disintegration of the cytoplasm which became cornified