Tetrandrine and Isotetrandrine, Two Bisbenzyltetrahydroisoquinoline Alkaloids from Menispermaceae, with Rat Uterine Smooth Muscle Relaxant Activity

Effect of xanthorrhizol, xanthorrhizol glycoside and trachylobanoic acid isolated from Cachani complex plants upon the contractile activity of uterine smooth muscle

Xanthorrhizol, xanthorrhizol glycoside, and trachylobanoic acid, compounds isolated from medicinal plants that are grouped in the complex known as Cachani have been shown to inhibit the tonic contraction of rat uterus induced by: (a) depolarizing K+ solution (60 mM), (b) CaCl2 (1 mM), and (c) BAY K 8644 (0.3 microM) in a concentration-dependent manner (1-30 micrograms/mL). The inhibitory potency was displayed as follows: xanthorrhizol > xanthorrhizol glycoside > trachylobanoic acid. These results suggest that the assayed compounds might block voltage operated calcium influx in myometrial cells as they displayed a calcium-antagonistic activity. This effect is not due to peripheral receptor activation (beta 2-adrenergic, H2-histaminergic) as neither propranolol nor cimetidine modified the inhibitory effect of the compounds assayed. This is the first report showing that plants belonging to the Cachani complex may contain uterine smooth muscle bioactive substances.

Alpha-adrenoceptor interaction of tetrandrine and isotetrandrine in the rat: functional and binding assays

The action of 1S,1'S-tetrandrine, a bisbenzyltetrahydroisoquinoline alkaloid, on alpha1-adrenoceptors has been compared with that of its isomer 1R,1'S-isotetrandrine. The work includes binding assays to analyse the affinity of these products for the [3H]prazosin binding site of rat cerebral cortical membranes and functional studies on rat isolated aorta to examine the effects of both alkaloids on intracellular calcium processes related or not to alpha-adrenoceptor activation. A radioligand receptor-binding study showed that both compounds interacted with the alpha1-adrenoceptors displacing [3H]prazosin from the specific binding site. The Ki values (inhibition constants) were 0.69+/-0.12 and 1.6+/-0.4 microM for tetrandrine and isotetrandrine, respectively. The functional studies showed that both alkaloids concentration-dependently inhibited noradrenaline-induced contraction in Ca2+-free solution (IC50 values, i.e. the concentrations needed to induce 50% inhibition, were 252.8 and 174.9 microM for tetrandrine and isotetrandrine, respectively), the spontaneous contractile response elicited by extracellular calcium after depletion of noradrenaline-sensitive intracellular stores (increase in resting tone; IC50 values 11.6 and 19.6 microM for tetrandrine and isotetrandrine, respectively) and the refilling of intracellular Ca2+ stores sensitive to noradrenaline (IC50 values 7.4 and 14.9 microM for tetrandrine and isotetrandrine, respectively). The results show that tetrandrine and isotetrandrine interact with alpha1-adrenoceptors by displacing the [3H]prazosin binding site and that both compounds inhibit mainly the Ca2+-dependent process and have less action on alpha1-adrenoceptors. Tetrandrine is more potent than isotetrandrine.

Flavanones with potent antibacterial activity against methicillin-resistant Staphylococcus aureus

With the therapeutic concept of using the defensive ability of plants against microbial infections, phytoalexin, an antimicrobial phytochemical was studied for its ability to inhibit the growth of methicillin-resistant Staphylococcus aureus (MRSA). Extracts from Sophora exigua (Leguminosae) were fractionated by serial chromatography and the anti-MRSA activity of each fraction was determined by the agar-plate method. Among the active isolates, 5,7,2',6'-tetrahydroxy-6-isoprenyl-8-lavandulyl-4'-methox yflavanone (exiguaflavanone D) completely inhibited the growth of all the MRSA strains examined at the concentration of 1.56-6.25 micrograms mL-1, and 5, 2',6'-trihydroxy-8-lavandulyl-7-methoxy-flavanone (exiguaflavanone B) inhibited at a concentration of 50 micrograms mL-1. This former compound is expected to be a phytotherapeutic agent for MRSA infections as an alternative to conventional antibiotics with unwanted side-effects or the appearance of antibiotic-resistant bacteria.

Comparative study of the rat uterine smooth muscle relaxant activity of three bisbenzyltetrahydroisoquinolines with tetrandrine

The relaxant activity of three bisbenzyltetrahydroisoquinolines--obaberine, popisonine and lindoldhamine--was examined in rat isolated uterus and 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 degree of methylation of the free phenolic hydroxy groups and the loss of one diarylether bridge influence the potency of relaxant action of these 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 Ca(2+)-free medium.

Different mechanism of relaxation induced by aporphine alkaloids in rat uterus

We have examined the uterine relaxant action of three aporphine molecules (S-glaucine, S-boldine and R-apomorphine) in two experimental conditions, with and without calcium in the bathing solution, and compared these effects with those obtained with the calcium antagonists verapamil and diltiazem. The present study shows that the alkaloids relax the uterine muscle but with different mechanisms of action. In Ca(2+)-containing solution all three alkaloids relaxed the uterus previously contracted by KCl or acetylcholine, but in Ca(2+)-free medium only R-apomorphine was able to relax oxytocin-induced contraction. The calcium antagonists, verapamil and diltiazem, relaxed KCl- or acetylcholine-induced contraction in Ca(2+)-containing solution, whereas they only relaxed oxytocin-induced contraction in Ca(2+)-free medium at much higher doses. These results suggest that glaucine and boldine behave as specific calcium entry blockers without affecting the contractile machinery or intracellular Ca2+ levels as apomorphine does. The absolute configuration (S-glaucine and S-boldine vs R-apomorphine) may account for this different action.