Inotropic action of tolbutamide on human myocardium.

The inotropic action of tolbutamide previously demonstrated in vitro was evaluated in 15 nondiabetic subjects during diagnostic cardiac catheterization. Following bolus injection of 250 mg of tolbutamide intravenously, a rise of serum insulin and a slight fall of serum potassium were observed. Inotropic response was determined from significant fall in PEP/LVET ratio, significant fall of left ventricular end-diastolic pressure, shift to an augmented function curve in work-pressure relationships, and prominent rise of dP/dt values at comparable heart rates. The inotropic effect was greatest at 5-15 min with return to near control values at 30 min. An unusually marked inotropic response was observed in one subject. While the measurable net hemodynamic effect of tolbutamide in the human heart is small, its effect on ischemic and normal areas within the heart of a diabetic patient with atherosclerosis may be different. Thus, its ultimate effect on the diseased heart may be significant.