Modulation of glucose metabolism by sulfonylureas in primary cultures of adult rat hepatocytes.

Addition of tolbutamide (0.1-5 microM) or glipizide (0.05-5 microM) to primary cultures of adult rat hepatocytes caused a dose-dependent increase of fructose 2,6-bisphosphate concentration. This effect was accompanied by a stimulation of the rate of L-lactate production and by an acceleration of the metabolic flux through the reaction catalysed by 6-phosphofructo 1-kinase. Moreover, the continuous presence of tolbutamide during the first 26 hours of culture mimicked long-term insulin effects by raising fructose 2,6-bisphosphate levels and the rate of L-lactate formation. Glucokinase, 6-phosphofructo 1-kinase and total 6-phosphofructo 2-kinase activities were not found to be significantly different in hepatocytes cultured either in the presence or in the absence of sulfonylurea.

Glipentide and glucose metabolism in isolated rat hepatocytes.

Glipentide, a second generation sulfonylurea, raised the cellular concentration of fructose 2,6-bisphosphate in isolated rat hepatocytes. Parallel to accumulating this regulatory metabolite, glipentide inhibited basal gluconeogenesis and increased the rate of L-lactate production, as well as the metabolic flux through the 6-phosphofructo 1-kinase reaction. Tolbutamide elicited similar metabolic effects to those reported for glipentide, although the latter sulfonylurea was about 10 times more potent. The biochemical mechanism by which sulfonylureas promote the accumulation of fructose 2,6-bisphosphate in hepatocytes seems to be related to a significant increase of the hexose 6-phosphate pool (glucose 6-phosphate plus fructose 6-phosphate), together with the activation of 6-phosphofructo 2-kinase and inactivation of fructose 2,6-bisphosphatase, enzyme activities responsible, respectively, for the synthesis and degradation of fructose 2,6-bisphosphate.