Apoptosis of endometrial cells in the bitch

The relationship between apoptosis of endometrial cells in the bitch, and the occurrence of degeneration of the endometrial luminal epithelium and regression of the endometrial glandular epithelium was determined. Mature bitches (n = 12) were ovariectomized and treated with hormones to simulate uterine changes that occur during the oestrous cycle. All bitches were treated with oestradiol benzoate (0.6–4.8 µg kg–1, i. m., twice per day) for 11–12 days then with progestagen (megestrol acetate, 2 mg kg–1, p. o., once per day) for 35–37 days. Bitches were treated daily for a further 3 weeks with megestrol acetate at dose rates of 0.5 mg kg–1 (decreased-dose group (n = 3)), 2 mg kg–1 (standard-dose group (n = 3)), or 3 (1 wk), 4 (1 wk) and 5 (1 wk) mg kg–1 (increased-dose group (n = 3)), or received no treatment (withdrawal-dose group (n = 3)). These bitches were necropsied at the end of the treatment period. A further 10, ovary-intact, bitches were necropsied when in oestrus (n = 1), dioestrus (n = 5), and at 3 weeks (n = 1) and 9 weeks (n = 3) of anoestrus. Degeneration of the luminal epithelium was observed in all bitches except those in oestrus, at 9 weeks of anoestrus and one in dioestrus. Apoptosis was observed in the glandular epithelial cells, stromal cells and endothelial cells of blood capillaries in all bitches except those at oestrous and at 9 weeks of anoestrous. High average apoptotic indices were detected in the basal glandular epithelium of the dioestrous, decreased-dose, standard-dose and increased-dose groups, whereas low apoptotic indices were detected at 3 weeks of anoestrous and in the withdrawal-dose groups. These results indicate that degeneration of cells of the glandular epithelium, but not of the luminal epithelium, was due to apoptosis of these cells.