The aims of this study were: (i) to establish a reliable model for the study of cystic
endometrial hyperplasia in ovariectomized bitches; and (ii) to assess the roles of oestrogen and
progesterone in the pathogenesis of
irritant-induced cystic
endometrial hyperplasia. Greyhound bitches (n = 15) were ovariectomized and divided into five groups (n = 3 per group). After 3-4 weeks,
oestradiol benzoate (0.6-4.8 micrograms kg-1, i.m.) was administered twice a day for 12 days to the bitches in group 1, followed by
progesterone (0.2-1.8 mg kg-1, i.m.) twice a day for 30-33 days. These dosages were chosen to mimic the plasma
hormone concentrations of a normal oestrous cycle. A
silk suture was inserted by
laparotomy into the left uterine horn 12 days into the simulated dioestrus (determined by vaginal cytology) and necropsy was performed after a further 12 days. For groups 2-5, the
silk suture was positioned at
ovariectomy. After a further 3-4 weeks, these bitches were treated with
progesterone (group 2: 1.8 mg kg-1 i.m. twice a day),
oestradiol benzoate (group 3: 0.6-4.8 micrograms kg-1 i.m. twice a day),
oestradiol benzoate and
progesterone together (group 4: previous dosages) or vehicle (group 5). Necropsies were performed after 12-13 days of treatment. Cystic
endometrial hyperplasia was induced in the
suture-containing uterine horns of all bitches in groups 1 and 4, and in two bitches in group 2. Cystic
endometrial hyperplasia did not develop in any control (no
suture) uterine horns, or in either uterine horn of the bitches treated with either
oestradiol only or vehicle. These results indicate that
progesterone is necessary for the development of
irritant-induced cystic
endometrial hyperplasia and that
oestradiol potentiates the effects of
progesterone. The protocol used for bitches in group 1 would be a suitable model for further studies of the pathogenesis of cystic
endometrial hyperplasia.