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

The L ‐arginine‐NO pathway has been implicated in the vasorelaxant effect of 17‐β‐oestradiol. Here we have addressed the involvement of two distinct activation steps of endothelial nitric oxide synthase (eNOS) in the 17‐β‐oestradiol‐induced vasorelaxant effect on rat aortic rings. Rat aortic rings contracted with phenylephrine (PE) 1 μ M relaxed in a concentration related fashion to 17‐β‐oestradiol water soluble cyclodextrin‐encapsulated (E2) only when endothelium was present. The pure anti‐oestrogen of E2 receptor ICI 182,780 (20 μ M ) significantly inhibited E2‐induced vasorelaxation. Geldanamycin (10 μ M ), a specific inhibitor of heat shock protein 90 (hsp90) and N ω ‐nitro‐ L ‐arginine‐methyl ester ( L ‐NAME, 100 μ M ), a nitric oxide synthase inhibitor, significantly inhibited E2‐induced vasorelaxation. Incubation of rat aortic rings up to 6 h with LY 294002 (25 μ M ), a specific inhibitor of PI(3)K akt/pkb pathway reduced E2‐induced vasorelaxation. Incubation of rat isolated aorta with E2, induced prostacyclin (PGI 2 ) release. PGI 2 levels, measured as 6‐keto PGF 1α , were abolished by ibuprofen (10 μ M ), both L ‐NAME and GA did not influence basal or E2‐stimulated PGI 2 confirming the specificity of these two compounds on eNOS pathway. 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.British Journal of Pharmacology (2002) 135 , 1695–1700; doi: 10.1038/sj.bjp.0704641