Ultrastructural Changes in Granulosa Cells in Porcine Antral Follicles Undergoing Atresia Indicate Apoptotic Cell Death

Abstract

Ultrastructural changes in follicular granulosa cells during atresia were examined in pig ovaries. No apoptotic cells were observed in healthy follicles. However, in follicles in the early stage of atresia apoptosis occurred in granulosa cells located on the inner surface of the follicular wall. In these apoptotic granulosa cells, nuclear condensation with large clumps of chromatin and cytoplasmic condensation but with retention of the integrity of organelles were observed by electron microscopy. As atresia progressed, pyknotic granulosa cells and apoptotic bodies increased in number in the follicular wall. In follicles in the late stage of atresia, apoptotic bodies were suspended in the follicular antrum. Concurrently, cell debris without distinct membranes but with condensed chromatin, degenerated apoptotic bodies, occurred in follicles. The apoptotic bodies and cell debris were occasionally surrounded and phagocytosed by neighboring granulosa cells. In follicles in the advanced stage of atresia, apoptotic bodies and cell debris were fed by macrophages.