Localization of apoptotic cells in the cystic ovarian follicles of cows: ADNA-end labeling histochemical study

We examined the frequency of apoptosis in cystic follicular cells to invest igate the cause of the delay in regression of cystic follicles. Paraffin se ctions of healthy antral follicles, early and late atretic ones, and early and late cystic ones were stained using the terminal deoxynucleotidyl trans ferase (Tdt)-mediated biotinylated deoxyuridine triphosphates (dUTP) nick e nd-labeling (TUNEL) method to detect apoptotic cells. In the granulosa laye r of early cystic and atretic follicles, TUNEL-positive cells were evident. In the theca interna of both early and late atresia, high frequencies of T UNEL-positive cells were observed. In the theca interna, a high frequency o f TUNEL-positive cells was noted in the early cystic follicles, whereas the ir frequency decreased in late cystic follicles. These results suggest that apoptosis occurs in the granulosa and theca interna cells of cystic as wel l as atretic follicles, but the frequency of apoptosis in theca interna cel ls decreases in late cystic follicles, which may be responsible for the del ay of follicular regression. (C) 2000 by Elsevier Science Inc.