COMPARATIVE-STUDY OF THE RAT UTERINE SMOOTH-MUSCLE RELAXANT ACTIVITY OF 3 BISBENZYLTETRAHYDROISOQUINOLINES WITH TETRANDRINE

The relaxant activity of three bisbenzyltetrahydroisoquibolines-obaber ine popisonine and lindoldhamine-was examined in rat isolated uterus a nd their inhibitory potencies were compared with that of tetrandrine. All alkaloids tested relaxed KCl-depolarized rat uterus and totally or partially inhibited oxytocin-induced rhythmic contractions. The degre e of methylation of the free phenolic hydroxy groups and the loss of o ne diarylether bridge influence the potency of relaxant action of thes e alkaloids. Only alkaloids with absolute configuration 1R,1'S or 1R1' R acted intracellularly, promoting relaxation of contractile responses induced by oxytocin or vanadate in a Ca2+-free MediUM.