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.