Effects of nutritional status and acute variation in substrate supply on cardiac and skeletal-muscle fructose 2,6-bisphosphate concentrations

We examined the long-term effects of nutritional status and the acute effects of changes in exogenous carbohydrate- and lipid-substrate supply and utilization on fructose 2,6-bisphosphate (Fru-2,6-P2) concentrations in heart, gastrocnemius and soleus. Starvation decreased Fru-2,6-P2 concentrations in all three muscles. The acute administration of insulin and glucose increased skeletal-muscle Fru-2,6-P2 in the fed, but not in the starved, state, but cardiac Fru-2,6-P2 was unchanged. Cardiac and skeletal-muscle Fru-2,6-P2 concentrations were unaffected by acute increases in fatty acid supply produced by the administration of corn oil plus heparin, or by acute decreases in fatty acid supply produced by inhibition of lipolysis. Differences in cardiac and skeletal-muscle Fru-2,6-P2 concentrations observed in response to starvation were not reversed by administration of glucose or glucose plus insulin, or by inhibition of lipolysis, even though changes in citrate (heart), acylcarnitine (heart) and glycogen (skeletal muscle) were observed. Concentrations remained low for at least 8 h after chow re-feeding, but the fed value was restored by 24 h.