Cell-specific localisation of apoptosis in the bovine ovary at different stages of the oestrous cycle

Apoptosis was localized in all ovarian cell types of 23 cows in various stages of the oestrous cycle, using the detection of active caspase-3, in situ end labelling (TUNEL) and DNA fluorescent staining (DAPI). Very few apoptotic cells were found in primordial, primary, secondary and vital tertiary follicles. In contrast, apoptosis in atretic tertiary follicles was much more frequent, and high apoptotic scores were recorded when using the TUNEL technique and lower scores with the caspase-3 assay. Cystic atretic follicles showed in general a higher apoptotic score than obliterative atretic follicles, with intermediate to high scores in granulosa cells and lower scores in theca cells. In corpora lutea, large and small lutein cells had intermediate to high scores using the caspase-3 assay, and intermediate to low scores using the TUNEL assay. Irrespective of the detection method, the scores were higher in lutein cells than in the capsular stroma cells. In all ovarian structures examined, variations in apoptotic scores were seen in the different cycle stages, suggesting a cycle-dependent influence on apoptosis, although correlations with plasma progesterone concentrations were low.