INCREASED IN-VITRO FATTY-ACID SUPPLY AND CELLULAR-TRANSPORT CAPACITIES IN COLD-ACCLIMATED DUCKLINGS (CAIRINA-MOSCHATA)

In cold-acclimated (CA) birds, lipids play a crucial role in regulator y thermogenesis by acting both as substrates for and activators of the rmogenic processes. The capacity to supply lipids to thermogenic tissu es, which could limit cold thermogenesis, was assessed in CA ducklings (5 wk old, 4 degrees C) and compared with thermoneutral controls (TN, 25 degrees C). In CA ducklings, basal lipolytic activity of adipose t issue fragments was higher (202 +/- 9 vs. 130 +/- 14 nmol glycerol rel eased . 100 mg tissue(-1) . h(-1), +55%) than in TN controls, while gl ucagon had a much higher stimulatory effect (+140 to +500% depending o n dose). This was consistent with increased plasma levels of nonesteri fied fatty acids (FA, +57%) and glycerol(+31%) in vivo. In vitro endot helial lipase activity per organ was higher in CA than in TN ducklings in red gastrocnemius muscle (6.3 +/- 0.6 vs. 3.5 +/- 0.3 mu eq nonest erified FA released per hour, +80%) and liver (+55%). The intracellula r FA-binding capacity of (12-18 kDa) proteins was higher in gastrocnem ius muscle (+43%) and liver (+74%) from CA ducklings. In gastrocnemius , it was linked to a higher content (21 +/- 2 vs. 15 +/- 2 mu g/mg pro tein, +37%) of an intracellular 15.4-kDa FA-binding protein. These in vitro results indicate that coordinated increases in FA supply from ad ipose tissue, cellular uptake of lipoprotein-derived FA, and intracell ular FA transport capacity occur in CA ducklings endowed with higher t hermogenic capacity and cold endurance.