Comparison of six new antidepressants on isolated rat atria

The effects of six new antidepressants were studied and compared as to their electromechanical properties on isolated rat atria. All of the compounds reduced rate and amplitude of contractions, depressed atrial excitability and prolonged the sinus node recovery time. They also inhibited the amplitude of the slow contractions elicited by isoprenaline in K-depolarized atria. In decreasing order, the relative order of potency found was: mianserin approximately equal to maprotiline approximately equal to lofepramine greater than nomifensine approximately equal to trazodone greater than viloxazine. On atrial transmembrane action potentials mianserin, maprotiline and viloxazine decreased amplitude and maximum rate of depolarization and shortened the duration and depolarized the resting membrane potential. All these effects are similar to those previously reported with imipramine and amoxapine. Thus, differences between the cardiodepressant effects of the newer and older antidepressants are only quantitative but not qualitative. Possible explanations of the lower incidence of cardiovascular complications with the newer compounds are discussed.