Vasodilator effects of liriodenine and norushinsunine, two aporphine alkaloids isolated from Annona cherimolia, in rat aorta.

The effect of two aporphines, liriodenine and norushinsunine, isolated from Annona cherimolia, were studied in the rat aorta in order to examine their mechanism of action. Both alkaloids (10(-7) - 10(-4) mol/l) showed relaxant effects on the contractions elicited by 10(-6) mol/l noradrenaline (NA) or 80 mmol/1 KCl, but, while liriodenine showed a nonspecific relaxant action on both spasmogens, norushinsunine was more potent on KCl-induced contraction. In Ca2+ free medium, both alkaloids (0.1 mmol/l) inhibited the responses elicited by NA, but not those elicited by caffeine. This inhibitory action occurred when the alkaloids were present during the release of the Ca2+ internal stores or during the refilling process. These results suggest that the two aporphines show a relaxant action in rat aorta which is mediated by an interaction with alpha1-adrenoceptors and an alteration of the Ca2+ entry via voltage-operated channels. Norushinsunine exhibits a certain degree of selectivity as an L-type Ca2+ channel blocker.