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      Atrial Natriuretic Peptide Induces Postprandial Lipid Oxidation in Humans

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          Abstract

          OBJECTIVE—Atrial natriuretic peptide (ANP) regulates arterial blood pressure. In addition, ANP has recently been shown to promote human adipose tissue lipolysis through cGMP-mediated hormone-sensitive lipase activation. We hypothesized that ANP increases postprandial free fatty acid (FFA) availability and energy expenditure while decreasing arterial blood pressure.

          RESEARCH DESIGN AND METHODS—We infused human ANP (25 ng · kg −1 · min −1) in 12 men (age 32 ± 0.8 years, BMI 23.3 ± 0.4 kg/m 2) before, during, and 2 h after ingestion of a standardized high-fat test meal in a randomized, double-blind, cross-over fashion. Cardiovascular changes were monitored by continuous electrocardiogram and beat-by-beat blood pressure recordings. Metabolism was monitored through venous blood sampling, intramuscular and subcutaneous abdominal adipose tissue microdialysis, and indirect calorimetry.

          RESULTS—ANP infusion decreased mean arterial blood pressure by 4 mmHg during the postprandial phase ( P < 0.01 vs. placebo). At the same time, ANP induced lipolysis systemically ( P < 0.05 vs. placebo) and locally in subcutaneous abdominal adipose tissue ( P < 0.0001 vs. placebo), leading to a 50% increase in venous glycerol ( P < 0.01) and FFA ( P < 0.05) concentrations compared with placebo. The increase in FFA availability with ANP was paralleled by a 15% increase in lipid oxidation rates ( P < 0.05 vs. placebo), driving a substantial increase in postprandial energy expenditure ( P < 0.05 vs. placebo).

          CONCLUSIONS—Our data identify the ANP system as a novel pathway regulating postprandial lipid oxidation, energy expenditure, and concomitantly arterial blood pressure. The findings could have therapeutic implications.

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          Most cited references39

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          Diabetes

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            CIRCULATION

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              Carnitine--metabolism and functions.

              J. Bremer (1983)
              Carnitine was detected at the beginning of this century, but it was nearly forgotten among biochemists until its importance in fatty acid metabolism was established 50 years later. In the last 30 years, interest in the metabolism and functions of carnitine has steadily increased. Carnitine is synthesized in most eucaryotic organisms, although a few insects (and most likely some newborn animals) require it as a nutritional factor (vitamin BT). Carnitine biosynthesis is initiated by methylation of lysine. The trimethyllysine formed is subsequently converted to butyrobetaine in all tissues; the butyrobetaine is finally hydroxylated to carnitine in the liver and, in some animals, in the kidneys (see Fig. 1). It is released from these tissues and is then actively taken up by all other tissues. The turnover of carnitine in the body is slow, and the regulation of its synthesis is still incompletely understood. Microorganisms (e.g., in the intestine) can metabolize carnitine to trimethylamine, dehydrocarnitine (beta-keto-gamma-trimethylaminobutyric acid), betaine, and possibly to trimethylaminoacetone. In some insects carnitine can be converted to methylcholine, presumably with trimethylaminoacetone as an intermediate (see Fig. 3). In mammals the unphysiological isomer (+) carnitine is converted to trimethylaminoacetone. The natural isomer (-)carnitine is excreted unchanged in the urine, and it is still uncertain if it is degraded in mammalian tissues at all (Fig. 2). The only firmly established function of carnitine is its function as a carrier of activated fatty acids and activated acetate across the inner mitochondrial membrane. Two acyl-CoA:carnitine acyltransferases with overlapping chain-length specificities have been isolated: one acetyltransferase taking part in the transport of acetyl and short-chain acyl groups and one palmitoyltransferase taking part in the transport of long-chain acyl groups. An additional octanoyltransferase has been isolated from liver peroxisomes. Although a carnitine translocase that allows carnitine and acylcarnitine to penetrate the inner mitochondrial membrane has been deduced from functional studies (see Fig. 5), this translocase has not been isolated as a protein separate from the acyltransferases. Carnitine acetyltransferase and carnitine octanoyltransferase are also found in the peroxisomes. In these organelles the enzymes may be important in the transfer of acyl groups, which are produced by the peroxisomal beta-oxidation enzymes, to the mitochondria for oxidation in the citric acid cycle. The carnitine-dependent transport of activated fatty acids across the mitochondrial membrane is a regulated process. Malonyl-CoA inh
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                Author and article information

                Journal
                Diabetes
                diabetes
                Diabetes
                American Diabetes Association
                0012-1797
                1939-327X
                December 2008
                : 57
                : 12
                : 3199-3204
                Affiliations
                [1 ]Experimental and Clinical Research Center, Charité and HELIOS-Klinikum, Berlin, Germany
                [2 ]Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut
                [3 ]Institut National de la Santé et de la Recherche Médicale, Unité 858, Institut de Médecine Moléculaire de Rangueil, Université Paul Sabatier, Toulouse, France
                [4 ]Department of Chemical Endocrinology, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands
                [5 ]Institute of Clinical Pharmacology, Hannover Medical School, Hannover, Germany
                Author notes

                Corresponding author: Jens Jordan, jordan.jens@ 123456mh-hannover.de

                Article
                57123199
                10.2337/db08-0649
                2584124
                18835931
                512b86e3-2e99-4cf5-9778-0463e327543c
                Copyright © 2008, American Diabetes Association

                Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See http://creativecommons.org/licenses/by-nc-nd/3.0/ for details.

                History
                : 15 May 2008
                : 16 September 2008
                Categories
                Metabolism

                Endocrinology & Diabetes
                Endocrinology & Diabetes

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