title: Leptin augments the acute suppressive effects of insulin on hepatic very low-density lipoprotein production in rats.
abstract: It is well established that leptin increases the sensitivity of carbohydrate metabolism to the effects of insulin. Leptin and insulin also have potent effects on lipid metabolism. However, the effects of leptin on the regulation of liver lipid metabolism by insulin have not been investigated. The current study addressed the effects of leptin on insulin-regulated hepatic very low-density lipoprotein (VLDL) metabolism in vivo in rats. A 90-min hyperinsulinemic/euglycemic clamp (4 mU/kg x min(-1)) reduced plasma VLDL triglyceride (TG) by about 50% (P < 0.001 vs. saline control). Importantly, a leptin infusion (0.2 microg/kg x min(-1)) in combination with insulin reduced plasma VLDL-TG by about 80% (P < 0.001 vs. insulin alone). These effects did not require altered skeletal muscle lipoprotein lipase activity but did include differential effects of insulin and leptin on liver apolipoprotein (apo) B and TG metabolism. Thus, insulin decreased liver and plasma apoB100/B48 levels (approximately 50%, P < 0.01), increased liver TGs (approximately 20%, P < 0.05), and had no effect on fatty acid oxidation. Conversely, leptin decreased liver TGs (approximately 50%, P < 0.01) and increased fatty acid oxidation (approximately 50%, P < 0.01) but had no effects on liver or plasma apoB levels. Importantly, the TG-depleting and prooxidative effects of leptin were maintained in the presence of insulin. We conclude that leptin additively increases the suppressive effects of insulin on hepatic and systemic VLDL metabolism by stimulating depletion of liver TGs and increasing oxidative metabolism. The net effect of the combined actions of insulin and leptin is to decrease the production and TG content of VLDL particles.
authors.affiliation: Department of Medicine, Division of Endocrinology/Metabolism, University of Pittsburgh, Pittsburgh, Pennsylvania 1526, USA.
authors.forename: Wan
authors.initials: W
authors.lastname: Huang
authors.forename: Anantha
authors.initials: A
authors.lastname: Metlakunta
authors.forename: Nikolas
authors.initials: N
authors.lastname: Dedousis
authors.forename: Heidi K
authors.initials: HK
authors.lastname: Ortmeyer
authors.forename: Maja
authors.initials: M
authors.lastname: Stefanovic-Racic
authors.forename: Robert M
authors.initials: RM
authors.lastname: O'Doherty
mesh_terms: D000818:Animals; D053299:Apolipoprotein B-100 / Q000378:metabolism; D053283:Apolipoprotein B-48 / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004357:Drug Synergism; D015309:Glucose Clamp Technique; D006946:Hyperinsulinism / Q000139:chemically induced; D007328:Insulin / Q000494:pharmacology*; D020738:Leptin / Q000494:pharmacology*; D050356:Lipid Metabolism / Q000187:drug effects; D008079:Lipoproteins, VLDL / Q000097:blood / Q000378:metabolism*; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D010084:Oxidation-Reduction / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D014280:Triglycerides / Q000097:blood / Q000378:metabolism
chemical_list: D053299:Apolipoprotein B-100; D053283:Apolipoprotein B-48; D007328:Insulin; D020738:Leptin; D008079:Lipoproteins, VLDL; D014280:Triglycerides