OBJECTIVETo study the vasorelaxant effect of procyanidin (PC) extracted from grape seeds on rabbit thoracic pulmonic rings in vitro.

METHODRabbits thoracic pulmonic rings were isolated, pre-contracted with noradrenalin (NA) and their responses to different concentrations of PC were investigated. The effects of endothelium and different signaling pathway inhibitors on PC-induced relaxation, including nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (L-NNA), methylene blue (MB), prostaglandin synthase inhibitor indomethacin (Indo) and blockage of the adrenergic beta-receptor propranolol (Prop), were also assessed.

RESULTPC change the resting tension of rabbit's pulmonic rings but caused an obvious dose-dependent relaxation in 1 x 10(-6) mol x L(-) NA precontracted pulmonic rings (r = 0.69, P < 0.01). The relaxant effect of PC was significantly reduced by removal of endothelium or by treatment with either 1 x 10(-4) mol x L(-1) L-NNA or 1 x 10(-5) mol L(-1) MB, but not by treatment with prostaglandin synthase inhibitor or blockage of the adrenergic beta-receptor. In addition, PC (20 mg x L(-1)) dropped the dose-effect curves of NA, KCl and respectively on pulmonic rings denuded endothelium. PC can also inhibit the vasoconstriction caused by NA in the first phase, but has no impact on the constriction induced by CaCl2 in the second phase.

CONCLUSIONPC has an endothelium-dependent vasorelaxation on isolated rabbit's pulmonic rings, which is possibly mediated by nitric oxide (NO) pathways and blockage of receptor operated and voltage dependent calcium channels.