[Relaxing effects of l-stepholidine on rat resistance arteries]

Bolus injection(i.v.) of l-stepholidine(l-SPD, 3 mg.kg-1) caused hypotension in anaesthetized rats. The blood pressure reduction was sustained for 46.3 +/- 14.1 min. In in vitro experiments, l-SPD induced a concentration dependent relaxation of rat mesenteric, cerebral, renal and coronary resistance arteries preconstricted with 125 mmol.L-1 KCl. l-SPD was least potent with cerebral resistance arteries with the -Log EC50 value being 4.25 +/- 0.22. The relaxation of l-SPD on mesenteric resistance arteries was the most potent with the -Log EC50 value being 4.76 +/- 0.15. The larger influence of l-SPD (100 mumol.L-1) on the contraction induced by KCl in mesenteric than in cerebral arteries was in line with the above results. It is indicated that l-SPD has a direct relaxation on visceral resistance arteries with some degree of selectivity and the relaxation would decrease total peripheral resistance and thus constitute an important cause of its hypotensive action.