Crude extract and purified components isolated from the stems of Tinospora crispa exhibit positive inotropic effects on the isolated left atrium of rats

Tinospora crispa has been used in folkloric medicine for the control of blood pressure. We previously found that an extract of Tinospora crispa and its constituents effect the heart rate and blood pressure in anesthetized rats. The aim was to investigate the effects and mechanisms of the Tinospora crispa extract and bioactive components on the rat isolated left atria. Air-dried stems of Tinospora crispa were extracted with water, followed by partitioning with chloroform, ethyl acetate, and finally by n-butanol. The n-butanol soluble material was concentrated and dried under reduced pressure and lyophilized to obtain a crude powder (Tinospora crispa extract). The active components of Tinospora crispa extract were separated by column chromatography and preparative HPLC. The effects and mechanisms of the n-butanol extract and the bioactive purified components (adenine, uridine, adenosine, salsolinol, tyramine, higenamine, syringin, (−)-litcubinine, borapetoside A, borapetoside B, borapetoside D and borapetoside E) were studied in isolated left atria from normal and reserpinized rats. Tinospora crispa extract caused an increase in the force of contraction of the electrical field stimulated left atrium. This effect was inhibited by propranolol, atenolol, ICI-118,551, phentolamine and atropine. The positive inotropic effect on the reserpenized isolated left atrium of the Tinospora crispa extract was significantly inhibited by propranolol, atenolol and ICI-118,551. Phentolamine, on the other hand, caused potentiation and the effect was inhibited when propranolol was also added. Higenamine caused an increase in the force of contraction of the electrical field stimulated left atrium and this effect was significantly inhibited by ICI-118,551 and atenolol but not by phentolamine. Reserpine did not significantly shift the concentration–response curve (C–R curve) of the inotropic effect of the higenamine. ICI-118,551 and atenolol caused a parallel shift of the C–R curve to the right of about 8 and 33 fold, respectively. At low concentrations salsolinol caused a slight increase in the force of contraction of the left atrium, but at higher concentrations a decrease was observed. The negative inotropic effect of salsolinol was significantly inhibited by propranolol and atropine. In the reserpinized isolated left atrium, the negative inotropic effect of salsolinol was potentiated and again this effect was significantly inhibited by propranolol and atropine. Tyramine caused