Oestrogen and progestagen treated ovariectomized bitches: a model for the study of uterine function

The aim of this study was to validate a model in ovariectomized bitches for the study of uterine function. Mature bitches (n = 21) were ovariectomized and treated with oestradiol benzoate (0.6-4.8 micrograms kg-1, i.m. twice each day) and then with progestagen (megestrol acetate, 2 mg kg-1, p.o. once a day) and were necropsied at stages simulating pro-oestrus (n = 2), oestrus (n = 2) and dioestrus (n = 2). Other bitches received oestradiol benzoate and then megestrol acetate and were necropsied 3 weeks (midanoestrous group, n = 2) and 9 weeks (late anoestrous group, n = 2) after treatment. Untreated bitches (n = 1 per group) served as controls. The treatments induced oestrous behaviour, vulvar swelling, vulval discharge, vaginal smears, plasma oestradiol concentrations and uterine histology similar to that reported in intact bitches at each stage of the oestrous cycle. Marked endometrial degeneration and increased numbers of endometrial leucocytes were observed in the mid-anoestrous group. The endometrium was repaired in the late anoestrous group. A suture was placed in the lumen of the uterus of another six bitches at ovariectomy. Four of these bitches were treated with oestradiol benzoate and then megestrol acetate. Two bitches with a suture but not treated with hormones served as controls. In the hormone-treated bitches the suture resulted in cystic endometrial hyperplasia in two bitches and in cystic endometrial hyperplasia with pyometra in two bitches. The control bitches showed no cystic endometrial hyperplasia or pyometra. We have established in the ovariectomized bitch a model simulating the normal oestrous cycle that will facilitate studies of uterine function. This model will be used to study further the mechanisms of the endometrial degeneration and the pathogenesis of cystic endometrial hyperplasia.