Noradrenaline Liberation from the Dog Heart In Vivo

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Abstract
The liberation of radioactive noradrenaline from the heart was studied in anesthetized open-chest dogs after a single injection of tritiated noradrenaline (15 μCi/kg in 1 ml Ringer) into the left anterior descending coronary artery. Radioactivity was counted in blood samples collected simultaneously from the coronary sinus and from one femoral artery. The output of radioactivity from the heart, i.e. the difference between the radioactivity of coronary sinus and femoral artery blood, decreased rapidly in the first 60 min until equilibrium between arterial and coronary sinus blood was reached. Bolus intracoronary injections of tyramine (10–100 μg) caused long-lasting dose-dependent increases in the output of radioactivity from the heart. After electrical stimulation of the left stellate ganglion (7 V, 2 ms, 2.5 min), the output of radioactivity from the heart increased markedly but rapidly returned to initial levels at the end of the stimulation period. The maximum liberation of radioactivity was observed at a frequency of 10 Hz corresponding to the optimal physiological responses in coronary sinus blood flow, left ventricular pressure, femoral arterial pressure, and heart rate. It appears that this preparation is sensitive enough to detect the liberation of noradrenaline after both drug-induced and electrical sympathetic nerve stimulation, and that it could be usefully applied to correlate various parameters of cardiac function with noradrenaline release from cardiac sympathetic fibers.

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