Effect of bisbenzylisoquinoline alkaloids from Mahonia aquifolium on the isolated rat aorta.

1. The extract from roots of Mahonia aquifolium as well as berbamine and oxyacanthine relaxed K(+)-precontracted rat aortal rings with IC50 values of about 20 mumol/l. 2. Relaxation was not inhibited by denudation of the endothelium or by premedication of the aortas with indomethacin, methylene blue or propranolol. 3. Berbamine and oxyacanthine inhibited contractions induced by noradrenaline, phenylephrine and serotonin in a non-competitive manner. Further, they competitively blocked calcium-induced contraction in Ca(2+)-free depolarizing PSS. 4. The blockade of calcium entry appears to be the main mechanism of the dilatory effect of the drugs tested, but their interaction with alpha-adrenoceptors could not be excluded.