The use of epostane in an attempt to reproduce cystic endometrial hyperplasia in the bitch.

The aetiology and pathogenesis of spontaneous cystic endometrial hyperplasia (CEH) in the bitch is not yet completely understood. Recent research based on the expression of uterine sex hormone receptors in spontaneous cases of CEH suggested that a temporary progesterone deficiency during late oestrus-early metoestrus may be responsible for the onset of CEH development. In the present study a temporary progesterone deficiency during late oestrus-early metoestrus was experimentally created using an inhibitor of progesterone synthesis, epostane. At day 49 of metoestrus, there was a significant reduction in the size of the uterine wall, mainly due to endometrial atrophy, and there was also a significant increase in the mucus-filled uterine lumen in the bitches that had been treated with epostane compared to the control bitches. No significant differences in the expression of sex hormone receptors was observed between the two groups. As no CEH developed in the epostane-treated bitches, an additional oestrogenic stimulus may be required to stimulate endometrial proliferation. Therefore, it is suggested that deficient luteinization of the corpus luteum may be the trigger in the pathogenesis of CEH, as the secretion of varying amounts of sex steroids depends on the degree of luteinization.