Effect of levamisole hydrochloride on the guinea-pig atrium

The effects of levamisole on the guinea-pig atrial preparation were determined. At 3 micrograms/ml, levamisole and lignocaine prevented electrically induced arrhythmia in 3 and 5 out of 5 preparations respectively. It was concluded that levamisole at the therapeutic anthelmintic dose would not abolish clinical atrial arrhythmia. Levamisole even at 3 micrograms/ml had definite salutary effect on the hypodynamic state induced by continuous electrical stimulation. The dose-related positive inotropic effect of levamisole 5-200 micrograms/ml was not antagonised by practolol but was absent in atria from reserpinized animals. Therefore, cAMP may not be involved in the positive inotropic effect. Levamisole antagonised verapamil-induced negative inotropic effect and no positive inotropic effect was observed when the Ca2+ content of the Ringer-Locke solution was below normal. These suggested that Ca2+ must be involved in the inotropic effect. The negative chronotropic effect due to levamisole was not antagonised by hexamethonium but was antagonised by atropine, thus indicating that stimulation of M1 or M2 receptors in the atria may be responsible.