The process of apoptosis in granulosa and cumulus cells of ovarian follicles during follicular atresia was investigated in multiparous pigs. In healthy follicles, no apoptotic cells were observed histochemically, and no DNA ladder formation or Ca2+/Mg2+-dependent endonuclease activity were detected biochemically in granulosa or cumulus cells. In the follicles in the early stage of atresia, apoptosis occurred in granulosa cells located on the inner surface of the follicular wall but not cumulus cells. DNA ladder formation was observed in granulosa but not cumulus cells, and high levels of endonuclease activity were demonstrated only in the granulosa cells. No endonuclease activity was detected in cumulus cells obtained from the same atretic follicles. These findings suggest a lack of apoptotic cell death in cumulus cells in atretic follicles in multiparous pig ovaries.
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