Ovarian follicle atresia is the periodic process in which immature ovarian follicles degenerate and are subsequently re-absorbed during the follicular phase of the menstrual cycle. Typically around 20 follicles mature each month but only a single follicle is ovulated. The rest undergo atresia. That single dominant follicle becomes a corpus luteum following ovulation.
Atresia is a hormonally controlled apoptotic process that depends dominantly on granulosa cell apoptosis.
To date, at least five cell-death ligand-receptor systems have been reported in granulosa cells to play a role in atresia regulation. They are:
In addition, two intracellular inhibitor proteins, cellular FLICE-like inhibitory protein short form (cFLIPS) and long form (cFLIPL), which were strongly expressed in granulosa cells, may act as anti-apoptotic factors.
It has been proposed that enhanced levels of Nitrogen oxide in rats can prevent atresia of the ovarian follicle, and depressed levels have the opposite effect.