Abstract

1. The changes occurring concurrently in coronary flow and heart contraction have been recorded continuously in the isolated perfused rabbit heart, before and after injections of varying doses of epinephrine, aminophylline, nitroglycerine and papaverine.

2. The results indicate that epinephrine per se exerts neither a significant direct coronary vasoconstrictor nor a coronary vasodilator action, but in most of the experiments the coronary flow per heart beat is decreased due to the mechanical effects of the myocardial stimulation. The usually observed increase in the rate of coronary flow in the rabbit heart after epinephrine appears to be a secondary effect resulting from the cardiac stimulation, and may be due to some metabolite released during the intense stimulation of the myocardium.

3. Aminophylline, nitroglycerine and papaverine, in suitable doses all induce direct coronary vasodilatation, and the rate of coronary flow per heart beat is increased. In addition, (a) small doses of aminophylline increase the rate and amplitude of the heart contractions; with large doses, these effects are accentuated and may even decrease the rate of coronary flow per heart beat; (b) small doses of nitroglycerine slow the heart rate but lead to little change in the amplitude of contractions, but with large doses, coronary flow per heart beat is markedly increased due to myocardial depression; (c) small doses of papaverine exert little effect on rate or amplitude, but with increasing doses the heart rate is progressively increased and the amplitude of the contractions reduced, due to a decrease in both systole and diastole; these changes may decrease the rate of coronary flow per heart beat.

The possible significance of the above findings is discussed.