A new kalium channel blocker of Chinese medicinal origin--benzyltetrahydropalmatine hydrochloride

Benzyltetrahydropalmatine hydrochloride (BTHP) exhibited antiarrhythmic action in animal models. I. Electrophysiological effects of BTHP were investigated in various heart preparations. 1) BTHP markedly prolonged functional refractory period and inhibited adrenaline-induced automaticity. It decreased spontaneously beating rate of right atrium and abolished ouabain-induced delayed afterdepolarization and triggered activity of papillary muscle. 2) In standard microelectrode and contractility experiments BTHP concentration-dependently prolonged the action potential duration (APD) and effective refractory period (FRP) between 1-100 mumol/L; the force of contraction remained unchanged. 3) In voltage clamp experiments BTHP 1-100 mumol/L inhibited in dose-dependent manner the Ik with IC50 of 13 mumol/L and inhibited also Is at high concentration. 4) In monophasic action potential (MAP) of feline ventricle MAPD50 and MAPD90 were prolonged by BTHP in normal myocardium, and shortened APD induced by ischemia and reperfusion was restored to normal level. 5) In ECG and His-bundle electrogram heart rate was reduced; P-R and A-H interval were prolonged, but H-V interval and V duration were unaffected. II. BTHP showed a competitive alpha 1-adrenoceptor-blocking effect with pA2 value of 5.8 and 5.86 in rat anococcygeus muscle and rabbit aortic strips respectively. Radioligand binding assays showed that BTHP had affinity for both alpha 1 and alpha 2-adrenoceptor. The results from these experiments show that BTHP is a new K+ channel blocker of Chinese medicinal origin with alpha 1-adrenoceptor-blocking action.

Blocking action of berberine on various receptors in rat anococcygeus muscle

The contractile responses of rat anococcygeus muscle to phenylephrine, acetylcholine and 5-hydroxytryptamine in relation to berberine and to their specific antagonists were studied separately. The effects of phenylephrine and acetylcholine were blocked by berberine as well as by atropine. But the alpha-blocking action of atropine was exhibited only at high concentration. The anococcygeus muscle response to phenylephrine was competitively inhibited by berberine with a PA2 value of 6.4. The contraction induced by acetylcholine was competitively inhibited by atropine (PA2 = 8.7), whereas berberine, which differs basically from atropine, shifted the dose-response curve for acetylcholine non-parallelly to the right with its maximal response reduced concomitantly. Its pD2(1) value was 4.6. This suggests that the antagonistic action of berberine may be exerted non-specifically through a site beyond the M-cholinergic receptor. Berberine also relaxed the contraction of anococcygeus muscle induced by 5-hydroxytryptamine. The contractile responses to histamine and isoprenaline were seen only at high concentration. In addition, the response to isoprenaline was little affected by propranolol in our experiment.

Studies on the calcium antagonistic action of tetrandrine: X VI. Hemodynamic effects of tetrandrine on conscious rats

Hemodynamic study of tetrandrine (Tet) in conscious rats showed that 15 mg/kg i.v. lowered BP, LVSP, +/- dp/dtmax, and (dP/dt)P-1. The degree of diminutions was nearly equal to that of BP during the initial period, while the LVEDP was elevated. But all these parameters (except -dp/dtmax) recovered gradually and earlier than BP, and LVEDP decreased to a level slightly lower than that of control. These results indicate that the hypotensive action of Tet is mainly due to its inhibition of cardiac contractility at the early period, but due to vasodilatation in the later stage. The HR was slowed down abruptly followed by a reflex acceleration, and than a gradual but sustained decrease in HR supervened with i.v. Tet. When large dose (40 mg/kg) of Tet i.v. caused a cardiac standstill with the R wave of ECG persisting for a few minutes, it means that an excitation-contraction decoupling occurred as that found on isolated myocardial preparation treated with verapamil and Tet.