In vitro evaluation of the beta-blocking and electrophysiological properties of mepindolol

The electrophysiological and beta-blocking effects of mepindolol have been examined in isolated guinea-pig preparations and sheep cardiac Purkinje fibers. Mepindolol did not show selectivity for blocking the chronotropic and inotropic responses to isoprenaline on isolated guinea-pig preparations, and was practically equally potent in blocking the effect of isoprenaline on isolated guinea-pig trachea. Mepindolol 10(-7) M fully antagonized the positive chronotropic effect of isoprenaline (10(-7) M) in Purkinje fibers. However, normal automaticity, action potential characteristics, effective refractory period, membrane responsiveness of Purkinje fibers were unaffected by mepindolol up to 10(-6) M. On the whole, mepindolol appears to be a potent beta-blocker with no cardioselectivity, exerting membrane depressant effect only at concentrations 100-1000 times higher than those exerting effective beta-blockade.