The inotropic action of tolbutamide and glyburide

The effect of glyburide on myocardial function in human beings is not known. We divided 37 normal male volunteers into five groups. Each group received either intravenous saline solution; 10 mg propranolol by intravenous push followed by 0.1 mg/min; 5 micrograms/kg/min dobutamine; 1000 mg or 1250 mg oral tolbutamide; or 5 mg glyburide. Comparable therapeutic blood levels were obtained. Myocardial function was assessed by measurement of work product (WP, systolic pressure times heart rate) and ejection fraction (EF) by means of radionucleotide ventriculography. There was no change in EF or WP after administration of saline solution and tolbutamide; propranolol decreased EF and WP; dobutamine and glyburide increased EF and WP. In summary, tolbutamide had no effect on myocardial contractility, whereas glyburide increased myocardial contractility as measured by ejection fraction.