Pharmacological actions of various inotropic agents.

The aim of this paper is to describe various positive inotropic drugs (except the cardiac glycosides) and to attempt a classification according to their mechanism of action. The most important drugs with established positive inotropic effect are summarized first. Present interest focuses on the development of new agents with sufficiently high oral bioavailability and long duration of action. Prenalterol is a beta 1-adrenergic drug which appears to fulfil these criteria. Of increasing importance are drugs which combine a positive inotropic and a vasodilator effect. These include mainly the methylxanthines and possibly also the beta 2-adrenoceptor stimulating agents salbutamol, terbutaline, fenoterol and pirbuterol. A positive inotropic and vasodilator effect is also produced by the new compounds amrinone and AR-L 115 BS. These drugs appear to resemble theophylline and other methylxanthines in that they also act mainly as phosphodiesterase inhibitors with a subsequent increase in cAMP without interference with alpha- or beta-adrenoceptors. The mechanism of the as yet only experimentally established positive inotropic effect of alpha-adrenoceptor stimulating agents, e.g. phenylephrine, is unknown. However, it is independent of the cAMP system and is not accompanied by changes in frequency.