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

The role of oestrogen receptor (ER) β in vascular function remains unclear. With the use of a specific ERβ antibody we have now, using immunocytochemistry, visualized ERβ 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 ERβ was observed. In these vessels endothelial cells also expressed ERβ. Vascular expression of the ERα subtype was lower than that of ERβ. In aorta and tail artery, no immunoreactivity towards ERα was observed, while in uterine vessels occasional medial smooth muscle and endothelial cells expressed this ER subtype. ERβ and α 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 ERα, as determined by immunocytochemistry, was supported by measurements of ERα levels by enzyme immunoassay. In the uterine artery, the level of ERα 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 ERβ was observed in the vascular wall of several parts of the vascular tree, while ERα predominantly was expressed in uterine vessels, suggesting that ERβ and α may have different roles in vascular function.