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APPETITE, OBESITY, DIGESTION, AND METABOLISM

Atrial natriuretic peptide contribution to lipid mobilization and utilization during head-down bed rest in humans

Cédric Moro,^1,2,3 Fabien Pillard,^1,2 Isabelle de Glisezinski,^1,2 Franois Crampes,^1,2 Claire Thalamas,⁴ Isabelle Harant,^1,2 Marie-Adeline Marques,^1,2 Max Lafontan,^1,2 and Michel Berlan^1,2,3

¹Institut National de la Santé et de la Recherche Médicale, U858, Laboratoire de Recherche sur les Obésités, Institut de Médecine Moléculaire de Rangueil, ²Université Paul Sabatier, Institut Louis Bugnard, IFR31, ³Faculté de Médecine, Laboratoire de Pharmacologie Clinique et Médicale, and ⁴Centre d'Investigation Clinique, Toulouse, France

Submitted 6 March 2007 ; accepted in final form 29 May 2007

Head-down bed rest (HDBR) increases plasma levels of atrial natriuretic peptide (ANP) and decreases norepinephrine levels. We previously demonstrated that ANP promotes lipid mobilization and utilization, an effect independent of sympathetic nervous system activation, when infused into lean healthy men at pharmacological doses. The purpose of the present study was to demonstrate that a physiological increase in ANP contributes to lipid mobilization and oxidation in healthy young men. Eight men were positioned for 4 h in a sitting (control) or in a HDBR position. Indexes of lipid mobilization and hormonal changes were measured in plasma. Extracellular glycerol, an index of lipolysis, was determined in subcutaneous adipose tissue (SCAT) with a microdialysis technique. A twofold increase in plasma ANP concentration was observed after 60 min of HDBR, and a plateau was maintained thereafter. Plasma norepinephrine decreased by 30–40% during HDBR, while plasma insulin and glucose levels did not change. The level of plasma nonesterified fatty acids was higher during HDBR. SCAT lipolysis, as reflected by interstitial glycerol, as well as interstitial cGMP, the second messenger of the ANP pathway, increased during HDBR. This was associated with an increase in blood flow observed throughout HDBR. Significant changes in respiratory exchange ratio and percent use of lipid and carbohydrate were seen only after 3 h of HDBR. Thus the proportion of lipid oxidized increased by 40% after 3 h of HDBR. The rise in plasma ANP during HDBR was associated with increased lipolysis in SCAT and whole body lipid oxidation. In this physiological setting, independent of increasing catecholamines, our study suggests that ANP contributes to lipid mobilization and oxidation in healthy young men.

lipolysis; lipid oxidation