The roles of progestagen and uterine irritant in the maintenance of cystic endometrial hyperplasia in the canine uterus

Cystic endometrial hyperplasia (CEH) was induced in the left uterine horns of 14 mature ovariectomised greyhound bitches with an intra-luminal silk suture (uterine irritant) and treatment with estradiol benzoate and megestrol acetate (to simulate stages of a normal canine estrous cycle). Right uterine horns served as suture-free controls. From Day 30 of simulated diestrus, bitches received treatments of suture removal (n = 4), progestagen withdrawal (n = 5) or both (n = 5). Necropsies were performed 3 or 9 weeks later. At 3 weeks, severe cystic endometrial hyperplasia was present in all (6/6) left horns and in no (0/6) right horns. At 9 weeks, the left horns in 5/6 of bitches subjected to progestagen-withdrawal had recovered (in varying degrees) from cystic endometrial hyperplasia, whereas no recovery was evident in the left horns of bitches (n = 2) that continued to receive progestagen. This study demonstrated that: (i) cystic endometrial hyperplasia was reversible upon withdrawal of progestagen; (ii) progestagen maintained cystic endometrial hyperplasia in the presence or absence of irritant; and (iii) persistent endometrial irritation in the absence of progestagen may not maintain cystic endometrial hyperplasia.