Beta 2-mediated changes in central haemodynamics, coronary circulation and myocardial metabolism in canine

The combined effect of terbutaline on systemic and coronary circulation was investigated in dogs to clarify its influence on myocardial oxygen supply and lactate balance. The dogs were anaesthetized and the chest opened. Coronary sinus blood flow and cardiac output were monitored by thermodilution, aortic pressure was measured by tip-transducer and heart rate by RR-interval on ECG, coronary sinus blood were analyzed for lactate, oxygen and carbon dioxide. Terbutaline caused a substantial systemic vasodilation and an increased heart rate, the total external cardiac work increased to a minor degree. Terbutaline increased arterial lactate concentration. Coronary vascular resistance was reduced after terbutaline. Even if myocardial perfusion pressure was reduced and an increased external cardiac work was present, no signs of myocardial distress was observed in lactate metabolism or coronary sinus oxygen content. In fact a tendency to increased myocardial aerobic metabolism was observed, as myocardial lactate consumption increased after terbutaline. Terbutaline seems to be a coronary vasodilator in dogs. However, the demand for oxygen secondary to both an increase in cardiac work and aerobic metabolism can be hazardous to the potentially ischaemic myocardium.