No abstract

Despite their lack of brown adipose tissue, 6-wk-old cold-acclimated muscovy ducklings (4 degrees C; CA) exhibit nonshivering thermogenesis (NST) in the cold. To determine the site of this NST, the regional distribution of blood flow was measured by the microsphere method in the thermoneutral zone (25 degrees C) and during acute exposure to cold (8 degrees C). Ducklings reared at thermal neutrality (TN), which use shivering to produce extra heat in the cold, were compared with CA ducklings, which substitute NST for shivering. Further, the contribution of skeletal muscle thermogenesis to the increased heat production in the cold was estimated by measuring leg muscle blood flow and arteriovenous difference in oxygen content [(a-v)O2] across the leg, enabling an estimation of muscle O2 consumption. During cold exposure, a similar increase in total leg muscle blood flow occurred in TN and CA ducklings (+127 and +130% respectively), while hepatic arterial blood flow increased less (+56 to +37%, respectively). This rise in blood flow was accounted for by an increase in cardiac output, which was smaller in CA than in TN ducklings, and in both groups by a redistribution of blood flow to the most thermogenic organs (skeletal muscles and liver). The (a-v)O2 across the leg was not changed by cold exposure, indicating that the increase in leg muscle O2 consumption resulted mainly from the increase in blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

Gastrocnemius subsarcolemmal and intermyofibrillar mitochondria were isolated from 5-week-old cold-acclimated and thermoneutral control ducklings. In vitro respiration (polarography) and ATP synthesis (bioluminescence) were determined at 25³C. Subsarcolemmal mitochondria showed a higher state 4 respiration and lower respiratory control and ADP/O ratio in cold-acclimated than in thermoneutral ducklings. Palmitate decreased the rate of ATP synthesis in both mitochondrial populations to about 30% of maximal but failed to abolish this process even at high concentrations. It is suggested that both expensive ATP synthesis and increased ATP hydrolysis could contribute synergistically to muscle non-shivering thermogenesis in cold-acclimated ducklings.z 1998 Federation of European Biochemical Societies.