Regulation of palmitate esterification/oxidation by glucagon in isolated hepatocytes: the role of alpha-glycerophosphate concentration.

Lipolysis was measured as the disappearance of [3H]glycerol previously incorporated into triacylglycerol, diacylglycerol and phosphatidic acid. There was no effect of glucagon on the lipolysis of any of these lipids. A transient increase in cellular alpha-glycerophosphate was induced by addition of glycerol during incubation. This resulted in an immediate and temporary decrease in oxidation and increase in esterification of palmitate while the uptake of palmitate from the incubation medium was unchanged. The change in alpha-glycerophosphate was also correlated with a transient drop in acyl-CoA and acylcarnitine. The lactate/pyruvate ratio was increased by the glycerol addition, but was still elevated for some while after the transient change in alpha-glycerophosphate. Similar effects were obtained by addition of dihydroxyacetone instead of glycerol. It is concluded that fatty acid esterification/oxidation can be changed by variations in the concentration of alpha-glycerophosphate, and that glucagon acts on lipid metabolism by decreasing the level of this metabolite.