RELAXANT PROPERTIES OF SOME APORPHINE ALKALOIDS FROM MAHONIA-AQUIFOLIUM

In the present study we tested the effect of four aporphine alkaloids, corytuberine, magnoflorine, isothebaine and isocorydine, on the isola ted rat aorta. Corytuberine and magnoflorine showed little effect as r elaxants in KCl- and noradrenaline-induced contractions. They did not inhibit the phenylephrine concentration-response curve (CRC). Isotheba ine and isocorydine showed relaxant properties in the rat aorta. They relaxed the contractions induced by nonradrenaline to a greater extent than those induced by KCl and they also inhibited the noradrenaline-i nduced contraction in calcium-free solution. These alkaloids competiti vely shifted the phenylephrine CRC to the right and non-competitively the serotonin CRC. They seemed to inhibit both the influx of calcium i nto the cell, preferentially through receptor-regulated calcium channe ls, and the release of calcium from intracellular stores. Moreover, th ey appear to be antagonists of alpha(1)-adrenoceptors. Study of struct ure-activity relationships of aporphine alkaloids in the inhibition of calcium influx via potential-operated Ca2+ channels yielded informati on indicative of the interaction of these substances with the benzothi azepine receptor.