Combined lack of estrogen receptors α and β affects vascular iNOS protein expression

Endothelial and vascular smooth muscle cells express both estrogen receptor (ER) alpha and beta. Recent findings indicate that vascular ERbeta and ERalpha may substitute for one another. Here, we investigate vascular morphology, contractility and protein expression in intact aorta from adult (4 months old) female mice lacking both ERalpha and ERbeta (DERKO). The body weights were 17% higher (P < 0.01) in DERKO than in wild-type mice. Vascular morphology, investigated in paraffin sections from aorta stained with hematoxylin-eosin or van Gieson, was identical in DERKO and wild-type mice. Endothelial cells were clearly visible in aorta of both DERKO and wild-type animals. Morphometric analysis of media thickness and wall to lumen ratio using a computerized image analyzing system demonstrated no differences between the two groups of mice. The vascular expression of endothelial nitric oxide synthase (eNOS, NOS III) and inducible nitric oxide synthase (iNOS, NOS II) was investigated using Western blotting. Aorta from both DERKO and wild-type mice expressed iNOS protein, but the iNOS expression was 3 times lower (P < 0.05) in DERKO compared to wild-type mice. No difference in eNOS protein level between the two groups of animals was observed. Force responses to noradrenaline, determined either in the absence or in the presence of the nitric oxide synthase inhibitor L-NAME and the cyclo-oxygenase inhibitor indomethacin, were unaffected by the lack of functional ERalpha/ERbeta. In summary, combined lack of functional ERalpha and ERbeta lowers the vascular expression of iNOS but has no effects on morphology, eNOS expression, and noradrenaline sensitivity in the intact aorta.