17-β-oestradiol-induced vasorelaxation in vitro is mediated by eNOS through hsp90 and akt/pkb dependent mechanism

1 The L-arginine-NO pathway has been implicated in the vasorelaxant effect of 17-beta-oestradiol. Here we have addressed the involvement of two distinct activation steps of endothelial nitric oxide synthase (eNOS) in the 17-beta-oestradiol-induced vasorelaxant effect on rat aortic rings. 2 Rat aortic rings contracted with phenylephrine (PE) 1 muM relaxed in a concentration related fashion to 17-beta-ocstradiol water soluble cyclodextrin-encapsulated (E2) only when endothelium was present. The pure anti-oestrogen of E2 receptor 10 182,780 (20 muM) significantly inhibited E2-induced vasorelaxation. 3 Geldanamycin (10 pm), a specific inhibitor of heat shock protein 90 (hsp90) and N-infinity-nitro-L-arginine-methyl ester (L-NAME, 100 muM), a nitric oxide synthase inhibitor, significantly inhibited E2-induced vasorelaxation. 4 Incubation of rat aortic rings up to 6 h with LY 294002 (25 muM), a specific inhibitor of PI(3)K akt/pkb pathway reduced E2-induced vasorelaxation. 5 Incubation of rat isolated aorta with E2, induced prostacyclin (PGI(2)) release. PGI(2) levels, measured as 6-keto PGF(1alpha), were abolished by ibuprofen (10 muM), both L-NAME and GA did not influence basal or E2-stimulated PGI(2) confirming the specificity of these two compounds on eNOS pathway. 6 In conclusion, we demonstrate that E2 interaction with its receptor is followed by a vasorelaxant effect in rat aortic rings mediated by eNOS activation through both hsp90 and akt/pkb dependent mechanisms.