Endothelium-independent vasorelaxant effect of dioclein, a new flavonoid isolated from Dioclea grandiflora, in the rat aorta

We have investigated the endothelium-independent vasorelaxant effect of the new flavonoid dioclein (5,2',5'-trihydroxy-6-7-dimethoxyflavanone) in the rat aorta. In endothelium-denuded vessels, dioclein induced a concentration-dependent relaxation of aortic rings precontracted with noradrenaline (IC50 = 3.5 +/- 0.89 x 10(-4) M) and KCl (IC50 = 5.2 +/- 1.2 x 10(-4) M). In the absence o f extracellular calcium, dioclein reduced the contraction induced by noradr enaline (maximal reduction approximately 33%) but not that induced by caffe ine. Dioclein also produced a concentration-dependent inhibition of the sus tained contractions induced by the phorbol ester 12-O-tetradecanoyl phorbol -13-acetate in normal (IC50 = 4.0 +/- 0.2 x 10(-4) M) and Ca2+-free solutio n (IC50 = 4.0 +/- 0.3 x 10(-4) M). The results indicate that the endothelium-independent vasorelaxant effect o f dioclein may be explained by inhibition of contractions dependent on acti vation of protein kinase C, voltage-dependent Ca2+ influx and on the releas e of intracellular Ca2+ stores sensitive to noradrenaline.