THE CARDIAC FACTOR IN THE "PRESSOR" EFFECTS OF RENIN AND ANGIOTONIN.

Upon the isolated hearts of cats perfused with Ringer-Locke solution renin produced no significant effect. Angiotonin, on the other hand, brought about decrease in coronary flow and increase in amplitude of beat without any consistent effect upon heart rate. Both renin and angiotonin augmented the cardiac output and raised the "arterial" pressure in the Starling heart-lung preparation; here too without influence on the heart rate. Electrocardiograms recorded before, during and after the pressor effects of renin and angiotonin in the anesthetized cat showed no abnormalities until the blood pressure had risen above 190 mm. Hg when various types of cardiac arrhythmias appeared. These were prevented, or normal rhythm was restored, by cutting the vagus nerves or injecting atropine. It is concluded that the "pressor" effects of renal pressor substances include direct stimulation of the myocardium and augmentation of ventricular beat. Unless these actions lead to excessive decrease in diastolic volume of the ventricles, the cardiac output will be increased. The significance of this in the production of the pressor effect is discussed.