VASODILATOR EFFECTS OF LIRIODENINE AND NORUSHINSUNINE, 2 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 exa mine their mechanism of action. Both alkaloids (10(-7)-10(-4) mol/l) s howed relaxant effects on the contractions elicited by 10(-6) mol/l no radrenaline (NA) or 80 mmol/l KCl, but, while liriodenine showed a non specific relaxant action on both spasmogens, norushinsunine was more p otent on KCl-induced contraction. In Ca2+-free medium, both alkaloids (0.1 mmol/l) inhibited the responses elicited by NA, but not those eli cited 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 s how a relaxant action in rat aorta which is mediated by an interaction with alpha(1)-adrenoceptors and an alteration of the Ca2+ entry via v oltage-operated channels. Norushinsunine exhibits a certain degree of selectivity as an L-type Ca2+ channel blocker.