The receptive endometrium is characterized by apoptosis in the glands

Apoptosis in the human endometrium up to now has been detected during themid to late luteal phase and therefore connected to the onset of themenstrual shedding. However, there is increasing evidence that regulatedapoptosis may be important during decidualization and implantation. Toinvestigate a possible role for apoptosis in the human endometrium and itsregulation, we correlated the immunolocalization of the apoptosisregulatory protein bcl-2 and the proliferation marker Ki67 to the in-situnuclear DNA fragmentation - a key feature of apoptosis - detected by usingthe terminal deoxynucleotidyl transferase- mediated dUTP nick-end-labelling(TUNEL) method during the menstrual cycle. Whereas proliferation andbcl-2-expression were predominantly detected in the glandular compartmentduring the proliferative phase, only single apoptotic cells could be shownduring this period. During the transformation of the endometrium (days15-19) proliferation and bcl-2 expression decreased markedly and there wasno sign of apoptosis. At the beginning of the implantation window (days19-20) we could detect the first signs of apoptosis in the glandularepithelia in the basalis, which extended to the functionalis during theluteal phase. Proliferation and bcl-2 expression are limited to the stromalcompartment comprising the large granular lymphocytes - during this time,and extend in parallel with apoptosis from the basal to the functionallayers. Apoptosis therefore may be related to the loss of the protectiveeffect of bcl-2 and may have significance for the establishment of anendometrium adequately prepared for successful implantation.