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Articles in PresS, published online ahead of print August 15, 2002
Am J Physiol Regu Physiol, 10.1152/ajpregu.00681.2001
Submitted on November 15, 2001
Accepted on August 9, 2002
1 Laboratoire de Physiologie des Regulations Energetiques, Cellulaires et Moleculaires, Centre National de la Recherche Scientifique - Universite Claude Bernard Lyon 1, Villeurbanne, France
* To whom correspondence should be addressed. E-mail: elodie.bedu{at}univ-lyon1.fr.
Thermogenic endurance and development of metabolic cold adaptation in birds may critically depend on their ability to synthesise and use fatty acids (FA) as fuel substrates. Hepatic lipogenesis and the capacity to oxidise FA in thermogenic tissues were measured in cold acclimated ducklings (Cairina moschata) showing original mechanisms of metabolic cold adaptation in the absence of brown adipose tissue, the specialized thermogenic tissue of rodents. The rate of FA synthesis from U-14C-glucose and from 1-14C-acetate, measured in incubated hepatocytes isolated from 5-wk-old thermoneutral (25°C, TN) or cold-acclimated (4°C, CA) fed ducklings, were higher than in other species. Hepatic de novo lipogenesis was further increased by cold acclimation with both glucose (+194%) and acetate (+111%) as precursor. Insulin slightly increased (+11-14%) hepatic lipogenesis from both precursors in CA ducklings while glucagon was clearly inhibitory (-29 to -51%). Enhanced de novo lipogenesis was associated with higher (+171%) hepatocyte activity of glucose oxidation and larger capacity (+50 to +100%) of key lipogenic enzymes. The potential for FA oxidation was higher in liver (+61%) and skeletal muscle (+29 to +81%) homogenates from CA than from TN ducklings suggesting that the higher hepatic lipogenesis may fuel oxidation in thermogenic tissues. Present data underline the high capacity to synthesise lipids from glucose in species like muscovy ducks susceptible to hepatic steatosis. Lipogenic capacity can be further increased in the cold and may represent an important step in the metabolic adaptation to cold of growing ducklings.
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