Immunocytochemical demonstration of oestrogen receptor β 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 immunocytochemistry, visualized ER beta in different parts of the vascular tree. In about 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 the 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 vessels 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 blood flow occurring during the cycle are independent of ER density. The regional distribution of ER alpha, as determined by immunocytochemistry, was supported by measurements of ER alpha levels by enzyme immunoassay. In the uterine 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 artery respectively). Thus, a prominent nuclear expression of ER beta was observed in the vascular wall of several parts of the vascular tree, while ER alpha predominantly was expressed in uterine vessels, suggesting that ER beta and alpha may have different roles in vascular function.