THE RESPONSE OF ISOLATED HYPODYNAMIC MYOCARDIUM TO INOTROPIC DRUGS

¹ Laboratories of Pharmacology and Toxicology, Yale University School of Medicine New Haven, Connecticut

The inotropic response of the isolated papillary muscle of the cat's right ventricle has been studied in relation to increasing concentrations of "cardiac glycoside." In a series of congeners of digitoxin it has been possible to obtain characteristic and reproducible results under certain specified conditions. Among the essential conditions is the preliminary production of a hypodynamic state; fresh muscle will not respond to digitoxin congeners in the "therapeutic" range of concentration. After calibration with a ouabain standard each individual papillary muscle can be assigned its own muscle constant, a. Then the fractional response, R, to any glycoside G, follows the equation:

log G + log M + log a = 0.5 log < R/(1 - R) >

where log M is the negative log-potency of the glycoside.