Patterns of apoptosis in the corpora lutea of the rat during the oestrous cycle, pregnancy and in vitro culture

Apoptosis is associated with regression of corpora lutea (CL) in a number o f species. The present work compared apoptotic rates, assessed by low molec ular weight DNA labelling, in rat CL of the oestrous cycle, pregnancy, the immediate post-partum period, and in vitro culture. Apoptosis was significa ntly related to cycle phase with peak activity at oestrus. This pattern was similar in CL formed from the most recent ovulation and from the two previ ous generations. Apoptosis was evident during pregnancy, albeit at low rate s. It declined on the day of parturition and increased on the following day . Apoptosis was greatly increased in cultured CL to reach 20-fold higher le vels than those achieved during the oestrous cycle or pregnancy. Collective ly, these results suggest that apoptosis has lesser significance in rat CL functional regression than in other species with more precipitate structura l changes. However, rat CL clearly retain the potential for high rates of a poptosis and so present a useful model for examining molecular mechanisms o f apoptotic cell death.