The beta-agonist drug tulobuterol decreases cardiac automaticity in the rat: comparison with isoproterenol.

The effect of the new beta-agonist drug tulobuterol, has been compared with isoproterenol in an experimental model of ectopic cardiac automaticity induced by local injury in the isolated right ventricle of the rat. Isoproterenol significantly increases ventricular automaticity even with the lowest concentrations tested (10(-9)M). Tulobuterol, at concentrations ranging from 10(-9)M to 10(-6)M do not induce any change on the automatic ventricular frequency. Nevertheless, at higher concentrations (10(-5) and 5 X 10(-5)M), tulobuterol decreases the experimentally induced ventricular automaticity. Our results suggest that the new beta-agonist drug tulobuterol does not increase ventricular automaticity but, in fact, decreases it.