Seasonal Changes in Immunoreactivity of Vascular Endothelial Factor and its Receptors VEGFR1 and VEGFR2 in the Uterus of Wild Ground Squirrels (Citellus dauricus Brandt)

In this study, we investigated the immunoreactivity of vascular endothelial growth factor (VEGF) and its receptors fit-1 (VEGFR I) and the kinase domain receptor (KDR/Flk-1, VEGFR2) in the uteri of the wild ground squirrels during the estrous period, early pregnancy and nonbreeding period. Cellular localizations of VEGF, VEGFR 1 and VEGFR2 were detected by immunohistochemistry, and total proteins were extracted from uterine tissue in the estrous period, early pregnancy and nonbreeding period for Western blotting analysis. In addition, plasma estradiol-17 beta and progesterone concentrations were measured by radioimmunoassay. Stronger positive staining of VEGF was found in luminal epithelial cells and glandular cells, and its receptors (VEGFR1 and VEGFR2) were observed in stromal cells in the estrous period and early pregnancy compared with the nonbreeding period. The protein levels of VEGF, VEGFR1 and VEGFR2 were significantly higher in the estrous period and early pregnancy as compared with the nonbreeding period. Besides, plasma estradio1-17 beta and progesterone concentrations were higher in the estrous period and early pregnancy than in the nonbreeding period, suggesting that the immunoreactivities of VEGF, VEGFR1 and VEGFR2 were correlated with changes in plasma estradiol-17 beta and progesterone concentrations. These results suggested that VEGF and its receptors may be involved in the regulation of seasonal changes in the uterine functions of wild female ground squirrels.