Proliferation and apoptosis of the bitch ovary during the different stages of the oestrous cycle

Abstract

In order to maintain homeostasis of the ovary, proliferation and apoptosis occur simultaneously in different ovarian cell types. It was shown that steroid hormone which changed during the oestrous cycle, may regulate these mechanisms in normal mammal ovarian tissues. Therefore, the present study was aimed to study cell proliferation and apoptosis during different stages of the oestrous cycle in the bitch ovary by using immunohistochemistry and TUNEL assay. The bitch ovaries were collected at 4 different stages of the oestrous cycle, which were prooestrus, oestrus, dioestrus and anoestrus. Immunohistochemistry and TUNEL assay were applied to detect Ki-67 protein and apoptosis respectively in different cells of the bitch ovary. The results showed that the most prominent staining for both Ki-67 and apoptosis was found in granulosa cells of the ovarian follicles. During the oestrous cycle, high proliferation was observed at prooestrus and oestrus in almost all ovarian cell types while no proliferating cell was found in the bitch corpus luteum. For apoptosis, high apoptotic rate was found at prooestrus in all ovarian cells except for luteal cells, in which apoptosis was significantly higher during dioestrus compared to the other stages. These results indicated that proliferation and apoptosis varied not only among different ovarian cells but also during the stages of the oestrous cycle, which may partly involve with the levels of ovarian steroid hormones. Moreover, the granulosa cells of the ovarian follicles were the most dynamic cell types which undergo proliferation and apoptosis during the oestrous cycle from the present study.