Differential vasoactive effects of oestrogen, oestrogen receptor agonists and selective oestrogen receptor modulators in rat middle cerebral artery

► The MCA relaxes on acute exposure to oestradiol, independent of endothelium and NO. ► Relaxation is not blocked by the classic ER antagonist or mimicked by novel SERMs. ► Relaxation was mimicked by selective agonist of ERα (PPT), ERβ (DPN) and GPR30 (G1). ► The rank order of potency was observed as follows: PPT > 17β-oestradiol > DPN > G1. ► The bulk of oestradiol relaxation is mediated by ERα bound to the plasma membrane. Cerebrovascular disorders are less common in pre-menopausal than post-menopausal women and in females than males. This protection may be due, in part at least, to direct effects of oestrogens on blood vessels. Oestrogen's vasodilatory mechanisms have been reported to be via the endothelium, vascular smooth muscle and extracellular matrix, depending on the vascular bed studied. Herein we investigated the vasoactive effects of oestrogen, oestrogen receptor (ER) and GPR30 agonists and selective ER modulators (SERMs) in the rat middle cerebral artery(MCA), an artery affected in focal ischaemia. MCAs isolated from male Sprague Dawley rats were mounted on a wire myograph. Concentration response curves were constructed to 17β-oestradiol, ERα agonist-PPT, ERβ agonist-DPN, GPR30 agonist-G1 and novel SERMs (LY362321 and LY2120310) in pre-constricted vessels, in the presence and absence of endothelium, blocking agents for nitric oxide synthase (L-NAME), classic ER antagonist (ICI182,780) or plasma membrane specific ERα (ERα-36) antibody. 17β-oestradiol induced rapid vasorelaxation of the MCA which was not affected by endothelium removal, L-NAME or ICI182,780. Vasorelaxation was mimicked by PPT, DPN and G1 but not by the SERMs. Using ERα-36 antibody, effects of oestrogen were partially blocked. PPT had a greater vasorelaxation, while DPN and G1 had a lesser effect than 17β-oestradiol. These findings indicate that activation of plasma membrane bound ERα, β and GPR30 elicits rapid, endothelial-nitric oxide-independent relaxation of the rat MCA.