Chlorpropamide Raises Fructose-2,6-Bisphosphate Concentration and Inhibits Gluconeogenesis in Isolated Rat Hepatocytes

Abstract

The addition of chlorpropamide to hepatocytes isolated from fed rats raised the cellular concentration of fructose-2,6-bisphosphate (F-2,6-P2), a regulatory metabolite that plays a relevant role in the control of hepatic glucose metabolism. The effect of chlorpropamide was dose dependent; a statistically significant increase was already seen at 0.2 mM of the sulfonylurea. The accumulation of F-2,6-P2 caused by chlorpropamide (1 mM) was parallel to the stimulation of L-lactate production (36.6 +/- 4.8 versus 26.1 +/- 2.6 mumol of lactate/g of cells X 20 min; N = 5, P less than 0.05) and to the inhibition of gluconeogenesis (0.57 +/- 0.1 versus 0.94 +/- 0.09 mumol of [U-14C]pyruvate converted to glucose/g of cells X 20 min; N = 5, P less than 0.05). In addition, chlorpropamide enhanced the inhibitory action evoked by insulin on glucagon-stimulated gluconeogenesis. This combined effect of chlorpropamide and insulin seems to be correlated with the synergistic accumulation of F-2,6-P2 provoked by the simultaneous action of these two agents on glucagon-treated hepatocytes. Finally, neither 6-phosphofructo-2-kinase activity nor hepatocyte cyclic AMP levels were significantly changed by the presence of the sulfonylurea in the incubation medium. Our results support the concept that chlorpropamide, by a cyclic AMP-independent mechanism, increases the hepatic content of F-2,6-P2 and, in this way, enhances the glycolytic flux and inhibits glucose output by the liver.

Regulation of muscle fructose 2,6-bisphosphate levels by sulfonylureas.

“…Sulfonylureas have been reported to stimulate glycogenesis and inhibit gluconeogenesis in the liver by itself or by enhancing insulin action (Fleig et al, 1984;Rinninger et al, 1984;Monge et al, 1986). In addition, the drug potentiates insulin-induced recruitment of glucose transport carrier in adipocytes (Jacobs and Jung, 1985) and enhances insulin action on glucose uptake in skeletal muscle (Feldman and Lebovitz, 1969;Daniels and Lewis, 1982).…”

Enhancement of blood glucose lowering effect of a sulfonylurea when coadministered with an ACE inhibitor: results of a glucose-clamp study

“…For example, one of the early sulfonylureas, chlorpropramide, demonstrated an inhibition of gluconeogenesis. This result, however, was only obtained in isolated rat hepatocytes -but not in humans [23]. Extra-pancreatic effects of sulfonylureas have only been described scarcely and are not regarded as of any clinical relevance [20].…”

Short-term regulation of glycolysis by vasoactive intestinal peptide in epithelial cells isolated from rat small intestine

“…Samples of cell incubations were deproteinized in HC1O4 (5 %, w/v) and subsequently neutralized [19]. Glucose, glucose 6-phosphate, L-lactate, ATP, ADP and AMP were determined spectrophotometrically in these extracts by enzymic methods [20].…”

“…Glucose, glucose 6-phosphate, L-lactate, ATP, ADP and AMP were determined spectrophotometrically in these extracts by enzymic methods [20]. For the measurement of Fru-2,6-P2, samples of cell suspension were frozen in liquid N2 and processed as previously described [19]. Fru-2,6-P2 was estimated by its ability to activate PPi: fructose-6-phosphate 1-phosphotransferase from potato tubers, by the method of Van Schaftingen et al [21].…”