Insulin and non-esterified fatty acids. Acute regulators of lipogenesis in perfused rat liver.

Livers from fed rats were perfused with whole rat blood and infused with oleate to maintain constant concentrations of serum non-esterified fatty acids over a wide physiological range. Infusion of insulin opposed the antilipogenic effects of increasing concentrations of serum non-esterified fatty acids. Secretion of very-low-density-lipoprotein triacylglycerols was directly proportional to the concentration of serum non-esterified fatty acids and was increased by insulin. The secretion of newly-synthesized fatty acids in very-low-density-lipoprotein triacylglycerols decreased with increasing concentrations of serum non-esterified fatty acid. Insulin opposed this change. Cholesterol biosynthesis was unaffected by alterations in concentration of serum non-esterified fatty acid but was increased by insulin. Equilibrium concentrations of perfusate lactate and glucose were increased by serum non-esterified fatty acids but steady-state rates of hepatic glucose output and lactate uptake were unchanged. Insulin decreased perfusate glucose concentrations and abolished the increase in its concentration that resulted from increases in non-esterified fatty acid concentrations.