In Vitro Effects of Carbutamide and Tolbutamide on Isolated Frog Muscle

¹ From the Department of Pharmacology, University of Virginia Medical School, Charlottesville, Virginia

Carbutamide and tolbutamide, sulfonylurea compounds which reduce the blood glucose concentration in intact animals, do not act like insulin in isolated frog muscle. Carbutamide, like sulfanilamide, inhibits the consumption of oxygen and increases the loss of potassium from the muscle. Tolbutamide greatly increases the oxygen consumption and decreases the loss of potassium from the tissue. These effects of tolbutamide are accompanied by a loss of muscle glycogen and an accumulation of lactate. Since the effect of tolbutamide on oxygen consumption can be inhibited with sodium azide, the extra oxygen is presumably used to oxidize the accumulating lactate and energy is thus provided to increase the influx of potassium into the tissue.