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ORIGINAL RESEARCH ARTICLE

Acute Central Infusion of Leptin Modulates Fatty Acid Mobilization by Affecting Lipolysis and mRNA Expression for Uncoupling Proteins

Department of Internal Medicine I, Faculty of Medicine, Oita Medical University, Hasama-machi, Oita 879-5593, Japan

To whom requests for reprints should be addressed at ¹ Department of Internal Medicine I, Faculty of Medicine, Oita University, Idaigaoka, Hasama, Oita, 879-5593 Japan. E-mail: hiroy{at}med.oita-u.ac.jp

Chronic administration of leptin has been shown to reduce adiposity through energy intake and expenditure. The present study aims to examine how acute central infusion of leptin regulates peripheral lipid metabolism, as assessed by markers indicative of their mobilization and utilization. A bolus infusion of 1 µg/rat leptin into the third cerebroventricle increased the expression of mRNA for hormone-sensitive lipase (HSL), an indicator of lipolysis, in white adipose tissue (WAT). This was accompanied by elevation of plasma levels of glycerol, but not of free fatty acids, as compared to the saline control (P < 0.03). The same treatment with leptin decreased plasma insulin levels but did not affect the plasma glucose level (P < 0.05 for insulin). Among the major regulators of the transportation or utilization of energy substrates, leptin treatment increased expression of mRNA for uncoupling protein 1 (UCP1) in brown adipose tissue (BAT), UCP2 in WAT, and UCP3 in quadriceps skeletal muscle, but not those for fatty acid–binding protein in WAT, carnitine phosphate transferase-1, a marker for ß oxidation of fatty acids in muscle, nor glucose transporter 4 in WAT and muscle (P < 0.01 for HSL, P < 0.05 for UCP1, and P < 0.005 for UCP2 and UCP3). These results indicate that, even in a single bolus, leptin may regulate the mobilization and/or utilization of energy substrates such as fatty acids by affecting lipolytic activity in WAT and by increasing the expression of UCPs in BAT, WAT, and muscle.

Key Words: leptin • uncoupling protein (UCP) • energy expenditure • lipolysis • hypothalamus

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