Morphological, histological and molecular investigations on canine uterine tissue after ovariectomy

In the present study, we investigated the course of atrophy in canine uterine tissue and the expression of estrogen receptors (ER) and progesterone receptors (PR) within 6 months after ovariectomy (OE). In nine primipar bitches of different breeds, bilateral OE and removal of one horn was performed. Six months after surgery, the remaining uterine tissue was removed. The tissue was examined for signs of inflammation and proliferation, and for expression of ER, PR and Ki67 by means of immunohistochemistry (IHC); furthermore transcription of vascular endothelial growth factor (VEGF), transforming growth factor-ß (TGF-ß), epithelial growth factor (EGF), platelet activating factor (PAF), tumor necrosis factor α (TNFα), and their specific receptors was determined by means of RT-qPCR. Serum concentrations of estrogen and progesterone were measured immediately before the first and second operation. Six month after OE, no inflammation was seen in any uterine tissue, the thickness of the stump was decreased in most bitches. Protein expression of Ki67 revealed high individual differences after the second operation. Concentration of both hormones was not significantly changed, the estrogen concentration always revealed high individual differences. The expression of ER was significantly decreased in stromal and smooth muscle cells of the uterine tissue (p < 0.01), and the expression of PR in stromal cells only (p < 0.05). The gene expression of growth factors did not change significantly between first and second operation. We conclude that complete atrophy did not occur within 6 months after OE, instead, a high percentage of uterine cells still expressed ER and PR, rendering the stump susceptible to hormone treatments.