Acute effects of leptin on glucose metabolism of in situ rat perfused livers and isolated hepatocytes RB Ceddia 1 , G Lopes 2 , HM Souza 3 , GR Borba-Murad 3 , WN William Jr 4 , RB Bazotte 2 and R Curi 4 * 1 Department of Physical Education, Fluminense Federal University, Nitero Âi, RJ, Brazil; 2 Department of Pharmacy and Pharmacology, University of Maringa Â, Maringa Â, PR, Brazil; 3 Department of Physiological Sciences, State University of Londrina, Londrina, PR, Brazil; and 4 Department of Physiology and Biophysics, University of Sa Äo Paulo, SP, Brazil OBJECTIVE: To investigate whether leptin interferes directly with glycogenolysis and gluconeogenesis in isolated rat hepatocytes and also in in situ rat perfused livers. ANIMALS: Male albino rats (200 ± 250 g) were used in all experiments. MEASUREMENTS: D-glucose, L-lactate and pyruvate production. RESULTS: In the present study, no differences were found for the rates of glycolysis, as expressed by the areas under the curves, among control (24.25.0 mmol =g), leptin (32.04.5 mmol =g), glucagon (24.73.0 mmol =g), and the leptin  glucagon (23.83.4 mmol =g) groups. No difference was found for the rates of glycogenolysis between the control and the leptin perfused livers (15.23.9 and 15.03.2 mmol =g, respectively). In the presence of glucagon, the areas under the curves for the rate of glycogenolysis rose to 108.63.8 mmol =g. When leptin was combined with glucagon, the area under the curve for glycogenolysis was 43.74.3 mmol =g. In fact, leptin caused a reduction of almost 60% (P<0.001) in the rate of glucagon-stimulated glycogenolysis. Under basal conditions, the addition of leptin (100 ng =ml) to the incubation medium did not elicit any alteration in glucose production by isolated hepatocytes. However, in the presence of leptin, the production of glucose from glycerol (2 mM), L-lactate (2 mM). L-alanine (5 mM) and L-glutamine (5 mM) by the isolated hepatocytes was signi®cantly reduced (30%, 30%, 23% and 25%, respectively). The rate of glucose production (glycogenolysis) by isolated hepatocytes was not different between the control and the leptin incubated groups (445.091.0 and 428.072.0 nmol =10 6 cells =h, respectively). CONCLUSION: We conclude that leptin per se does not directly affect either liver glycolysis or its glucose production, but a physiological leptin concentration is capable of acutely inducing a direct marked reduction on the rate of glucagon-stimulated glucose production in in situ rat perfused liver. Leptin is also capable of reducing glucose production from different gluconeogenic precursors in isolated hepatocytes. Keywords: leptin; gluconeogenesis; glycogenolysis; hepatocyte Introduction The discovery of the ob gene, 1 and also the properties of its product, leptin, have shed new light on the regulation of body weight and energy metabolism. Obesity has been largely related to insulin resistance, and the treatment of ob=ob mice 2±4 with leptin injec- tions has promoted marked reductions in body weight, glycaemia, and insulinaemia. Pair-feeding studies 5 and experimental hyperleptinaemic animal models 6 provide evidence that leptin exerts adipose-reducing effects in excess of those induced by decreases in food intake, suggesting a signi®cant metabolic regulation role for leptin, in addition to appetite suppression. Additionally, it has been reported that OB-R receptors, known to be expressed in the hypothalamus, are also present in peripheral tissues such as adipo- cytes, skeletal muscle and liver. 7,8 Based on these ®ndings it has been hypothesized that leptin may interfere with glucose metabolism by acting directly on peripheral tissues. In fact, it has been reported that leptin exerts a direct effect on glucose metabolism in skeletal muscle 9 and also in isolated adipocytes. 10 In vitro studies with human hepatic cell lines (HepG2, HepG3) and the rat hepatoma cell line H4- II-E 11 have reported that leptin causes attenuation of several insulin-induced effects. Contrary ®ndings have also been provided with rat (H-35) and human (HepG2) hepatoma cell lines expressing the long form of the leptin receptor (OB-R L ). 12 The presence of leptin did not cause any signi®cant alteration in insulin effects on these hepatoma cells, 12 therefore not contributing to the diabetic symptoms associated with obesity. In vivo (euglycaemic hyper-insulinaemic clamp) studies 13 have demonstrated that an acute increase in plasma leptin enhances the inhibitory effect of insulin on hepatic glucose production, and induces a *Correspondence: R Curi, Department of Physiology and Biophysics, Institute of Biomedical Sciences, Av. Prof. Lineus Prestes, 1524, University of Sa Ä o Paulo, USP, Sa Ä o Paulo, Brazil, 05508-900 E-mail: ruicuri@®sio.icb1.usp.br Received 25 November 1998; revised 2 June 1999; accepted 27 July 1999 International Journal of Obesity (1999) 23, 1207±1212 ß 1999 Stockton Press All rights reserved 0307±0565/99 $15.00 http://www.stockton-press.co.uk/ijo