Régulation du métabolisme lipidique des tissus adipeux et musculaires chez le ruminant. Effets du niveau alimentaire et de la photopériode

Abstract

The respective effects of feeding level and photoperiod variations on lipid metabolism and nutrient partitioning between ruminant adipose tissue and muscle are reviewed, with a particular interest in lipogenic enzymes and lipoprotein lipase gene expression in the cow and the ewe. Underfeeding decreases de novo fatty acid synthesis and lipoprotein lipase activity in adult and growing ruminant adipose tissues. Refeeding partially or totally reverses these effects. The lipoprotein lipase activity is not modified by underfeeding in the glycolytic Longissimus thoracis muscle, but is decreased in the oxidative cardiac muscle of adult ovine and bovine animals. Refeeding increases lipoprotein lipase activity in these two muscle types. Feeding level alters lipoprotein lipase in the same way in adipose tissues and muscles of ruminants, contrary to observations usually made in the rat. However, variations in lipoprotein lipase mRNA level in adipose tissue and muscle are parallel to those of lipoprotein lipase activity in the different animal species. These results at least partly suggest a pretranslational regulation in the expression of the lipoprotein lipase gene. Photoperiod directly affects adipose tissue and muscle metabolic activities in ewes. Indeed, lipogenic capacities in adipose tissue and lipoprotein lipase activity in glycolytic muscle are increased by long days. Inversely, lipomobilisation is increased by short days. These metabolic adaptations are probably involved in physiological adaptations of ewes to seasonal changes in food availability.