title: Mechanisms underlying biochanin A-induced relaxation of the aorta differ between normotensive and hypertensive rats.
abstract: 1. The aim of the present study was to investigate the mechanism underlying biochanin A-induced relaxation of the aorta in spontaneously hypertensive rats (SHR). 2. The tension in isolated ring preparations of thoracic aortas from normotensive (Wistar-Kyoto (WKY) rats) and SHR at 5 and 10 weeks of age was measured isometrically. 3. Biochanin A (10(-7) to 10(-4) mol/L) induced a concentration-dependent relaxation in aortic rings from both strains at the age of 5 and 10 weeks and the relaxation was greater in rings from 10-week-old SHR compared with age-matched WKY rats. The vasorelaxation induced by biochanin A was significantly reduced by denudation of the endothelium in aortic rings from SHR, but not WKY rats. Treatment with either indomethacin, a cyclo-oxygenase inhibitor, or N(omega)-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, had little effect on the relaxation induced by biochanin A in aortic rings from either strain. Glibenclamide, a selective inhibitor of ATP-sensitive potassium channels, significantly attenuated the relaxation induced by biochanin A in aortic rings from both strains, although the extent of reduction was greater in WKY rats than SHR. Conversely, treatment with 4-aminopyridine, a selective inhibitor of voltage-dependent potassium channels, or tetraethylammonium, an inhibitor of calcium-activated potassium channels, significantly reduced the vasorelaxation induced by biochanin A in rings from SHR but not WKY rats. 4. The greater vasorelaxation produced by biochanin A in aortic rings from 10-week-old SHR is endothelium dependent. Different mechanisms underlie the relaxant effects of biochanin A in aorta from SHR and WKY rats. The mechanisms of biochanin A-induced vasorelaxation in thoracic aortas from both normotensive and hypertensive rats involve ATP-sensitive potassium channels and, in addition, in rings from the hypertensive strain at 10 weeks of age, an endothelium-derived activation of smooth muscle cell potassium channels contributes to the vasorelaxation observed.
authors.affiliation: Department of Physiology, Zhejiang University School of Medicine, Hangzhou, China.
authors.forename: Hui-Ping
authors.initials: HP
authors.lastname: Wang
authors.forename: Qin
authors.initials: Q
authors.lastname: Gao
authors.forename: Ru-Huan
authors.initials: RH
authors.lastname: Mei
authors.forename: Meng-Hui
authors.initials: MH
authors.lastname: Zhao
authors.forename: Yuan
authors.initials: Y
authors.lastname: Lu
authors.forename: Xu-Yun
authors.initials: XY
authors.lastname: Li
authors.forename: Iain C
authors.initials: IC
authors.lastname: Bruce
authors.forename: Qiang
authors.initials: Q
authors.lastname: Xia
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000187:drug effects*; D001794:Blood Pressure / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D019833:Genistein / Q000494:pharmacology / Q000627:therapeutic use*; D006339:Heart Rate / Q000187:drug effects; D006973:Hypertension / Q000188:drug therapy*; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D026902:Potassium Channel Blockers; D009599:Nitroprusside; D019833:Genistein; D000109:Acetylcholine; C004541:biochanin A; D019331:NG-Nitroarginine Methyl Ester; D007213:Indomethacin