Immunolocalization of vascular endothelial growth factor, its receptors (flt1/fms, flk1/KDR, flt4) and vascular endothelial growth inhibitor in the bitch uterus during the sexual cycle

Angiogenesis is regulated by proangiogenic and antiangiogenic factors. Vascular endothelial growth factor (VEGF) is a prime proangiogenic regulator, whereas vascular endothelial growth inhibitor (VEGI) is a specific antiangiogenic cytokine. To clarify temporal changes in the localization of pro-angiogenic and anti-angiogenic factors in the uterus of normal bitches during the proestrus, estrus, diestrus and anestrus phases of the estrous cycle, the expressions of VEGF and its receptors (flt1/fms, flk1/KDR and flt4) and their correlation with VEGI were analyzed using immunohistochemistry. Uteruses were collected after ovariohysterectomy. Immunohistochemical staining was evaluated semi-quantitatively by an immunohistochemical total score consisting of the sum of the intensity and proportional scores. The results in the bitch uterus demonstrated that positive immunohistochemical staining was found exclusively in the cytoplasm and apical membrane of luminal and glandular epithelial, stromal and smooth muscle cells and nuclear staining was observed in the flt1/fms, flk4 and VEGI during proestrous and estrous. Semi-quantitative analyses revealed that the total score for VEGF in the glandular epithelial cells was significantly higher than that of luminal, endometrial stromal and myometrial smooth muscle cells during proestrous (p < 0.05). The total score for flk1/KDR and flt4 in the glandular epithelium was also significantly higher than that of endometrial stromal cells during proestrous, whilst the total score for flt1/fms in the glandular epithelium was significantly higher than that of endometrial stromal cells during anestrus (p < 0.05). We conclude that, in the bitch uterus, cyclic changes may be precisely regulated by the combined functions of VEGF family members, angiogenic VEGF and VEGF receptors, and the angiogenesis inhibitor VEGI.