The aim of this study is the histological characterization of the atretic process of follicles in pig ovary. Two mechanisms have been found. In the atretic preantral follicles changes are produced in the oocyte, in the granulosa cells, an in the newly formed theca. Three histological phases can be distinguished during atresia in preantral follicles. The principal observed modification is the loss of the connections among granulosa cells that acquire a star-shaped aspect. Few apoptotic cells were observed. In the atretic antral follicles four histological phases were characterized. The presence of apoptotic cells increases progressively in the first three. A peculiar distribution of apoptotic cells in the granulosa as well as in the theca were observed in all phases.
In conclusion: A) During atresia of antral follicles in porcine many apoptotic cells were observed in the granulosa and in the theca. B) Very few apoptotic cells were found during atresia in the preantral follicles. The possible existence of some other cell death mechanism different from apoptosis which may participate in the atresia of this type of follicles is proposed.