Uterine oestrogen and progesterone receptor expression in experimental pyometra in the bitch.

Pyometra was induced in five bitches by the intraluminal inoculation of a ligated uterine horn in metoestrus with an Escherichia coli suspension, the other horn serving as an uninoculated control. Histologically, the inoculated horns resembled those with naturally occurring pyometra, while the uninoculated horns had an inactive appearance instead of the normal metoestrus appearance. Immunohistochemically, the expression of sex hormone receptors in the inoculated horns corresponded with that in natural cases of pyometra. In the uninoculated horns, virtually no expression of sex hormone receptors was observed, in contrast to such expression in normal metoestrus. Bacteria-associated ovario-uterine interactions may have been responsible for the hyperplastic (inoculated horn) and inactive (uninoculated horn) uterine changes observed in this experiment.