Immunocytochemical demonstration of oestrogen receptor beta in blood vessels of the female rat

The role of oestrogen receptor (ER) B in vascular function remains unclear. With the use of a specific ER beta antibody we have now, using immunocytoc hemistry, visualized ER beta in different parts of the vascular tree. In ab out 70% of medial smooth muscle cells of female rat aorta, tail artery and uterine artery, nuclear immunoreactivity to ER beta was observed. In these vessels endothelial cells also expressed ER beta. Vascular expression of th e ER alpha subtype was lower than that of ER beta. In aorta and tail artery , no immunoreactivity towards ER alpha was observed, while in uterine vesse ls occasional medial smooth muscle and endothelial cells expressed this ER subtype. ER beta and alpha expression in uterine vessels was independent of the stage of the oestrous cycle, suggesting that variations in uterine blo od flow occurring during the cycle are independent of ER density. The regio nal distribution of ER alpha, as determined by immunocytochemistry, was sup ported by measurements of ER alpha levels by enzyme immunoassay. In the ute rine artery, the level of ER alpha was several times higher (P <0.001) than that of aorta and tail artery (10.1 +/- 1.7 fmol/mg protein in the uterine artery vs 3.3 +/- 1.0 and 0.5 +/- 0.5 fmol/mg protein in aorta and tail ar tery respectively). Thus, a prominent nuclear expression of ER beta was obs erved in the vascular wall of several parts of the vascular tree, while ER alpha predominantly was expressed in uterine vessels, suggesting that ER be ta and alpha may have different roles in vascular function.