1. The effect of an intravenous infusion of ouabain 0·25 μg min−1 kg−1 for 1 h on plasma insulin and blood glucose concentrations in peripheral venous blood and on urinary excretion of catecholamines was studied in six normal adult males. Ouabain had no effect on insulin and glucose concentrations but resulted in a significant decrease in urinary catecholamine excretion.
2. The effect of a single intravenous injection of 001 mg of ouabain/kg on the response of insulin secretion to intravenous tolbutamide was studied in four normal adult males. Ouabain had no significant effect on the increase of plasma insulin which followed tolbutamide.
3. These results indicate that improvement in insulin secretion observed during digitalis-induced remission in heart failure is probably due to the improved circulatory state of the patient and not to a direct insulin secretogogue effect.
4. The mechanisms responsible for decreased catecholamine excretion after ouabain in normal man are unexplained.