Steroidogenic activity and ultrastructural observation of atretic follicles in the cycling hamster ovary

In mature hamster ovaries, many follicles undergo atresia and this atretic change occurs in any estrous day. In this study, the localization of enzymes involved in estrogen biosynthesis, Bromodeoxyuridine (BrdU) incorporation, and Proliferating Cell Nuclear Antigen (PCNA) were immunohistochemically examined in the atretic follicles always provided with an atrum variable in size. Moreover, the granulosa cells from the atretic follicle in various but parallel stages of development were examined by scanning and transmission electron microscopes. Very early morphological signs of atresia in these follicles was the pyknotic change of a few granulosa cells lining the antral cavity. In this kind of follicles, the number of BrdU incorporating granulosa cell was decreased and the immunoreactivity of PCNA and aromatase was gradually decreased. Even in the early stage of atresia, some granulosa cells showed a remarkable morphological change characteristic of apoptosis as revealed by scanning and transmission electron microscopy.