Positive inotropic and toxic action of direct lytic factor on isolated working guinea pig hearts

The positive inotropic and the toxic effects of direct lytic factor (DLF) on the isolated working guinea pig hearts were studied. As compared with baseline values, DLF 1-10 micrograms.ml-1 increased aortic flow up to 138% cardiac output 116%, left ventricular pressure volume work 136%, left ventricular pressure 114%, dP/dtmax 130%, Vmax 128%, and mean aortic systolic pressure 114%, but coronary flow was decreased by 16% on an average (n = 6). However, heart rate remained constant, myocardial oxygen consumption and efficiency were changed little. The cardiotonic effect of DLF was also observed by recording the isometric contractions of the isolated guinea pig papillary muscles and by determining the left ventricular pressure and dP/dtmax in anesthetized dogs. Neither spontaneously beating rate of right atrium nor the excitability of left atrium in vitro was affected by DLF. The results show that DLF is one of the cardiotonic agents without chronotropic effect and its coronary vasoconstriction effect plays an important part in heart failure.