Acute tolbutamide administration alone or combined with insulin enhances glucose uptake in the perfused rat hindlimb.

Abstract

We examined the effects of acute administration of tolbutamide on glucose uptake in the non-cyclically perfused rat hindlimb. During the hour of study, 500 microunits boluses of insulin were given every ten min in the presence or absence of 3 X 10(-3)M tolbutamide. Tolbutamide by itself increased glucose uptake; however at no time was this increase significantly different from that seen in the group which received insulin alone. After 42 min of perfusion, the insulin-stimulated uptake was 26% and the tolbutamide was 20% greater than control (1.90 +/- 0.08, 1.80 +/- 0.06, and 1.50 +/- 0.05 mumol/min/100 g respectively). After 20 min of perfusion, the increase in glucose uptake seen with the combination of insulin + tolbutamide was significantly greater than that obtained with either tolbutamide or insulin alone. At the termination of perfusion, the glucose uptake with the combined treatment was 59% greater than control, 35% greater than tolbutamide, and 19% greater than insulin alone (2.67 +/- 0.10, vrs. 1.68 +/- 0.07 vrs. 1.97 +/- 0.07 vrs. 2.16 +/- 0.07 mumol/min/100 g). These results demonstrate not only a direct effect of tolbutamide, but also a potentiation of insulin-stimulated glucose uptake in the rat hindlimb. Therefore, tolbutamide has extra-pancreatic effects which probably contribute to the hypoglycemic action of this sulfonylurea.