Cold-acclimated Ducklings Research Articles

Increased respiration in skeletal muscle mitochondria from cold-acclimated ducklings: Uncoupling effects of free fatty acids

1. 1. Intermyofibrillar mitochondria from skeletal muscle (m. gastrocnemius) and liver mitochondria were isolated from cold-acclimated (4°C) or control (30°C) 4-week old ducklings. 2. 2. The respiratory rate of isolated mitochondria, with Na-succinate as substrate, was followed polarographically at 25°C in order to determine the basal respiratory rate, the rate of respiration in the presence of free fatty acids (FFA) (Na-palmitate), and the fully uncoupled rate, after addition of FCCP. 3. 3. The basal respiration (which in liver mitochondria was unaffected by acclimation to cold) was higher (+53%) in intermyofibrillar mitochondria from cold-acclimated ducklings than from controls, and the maximal FCCP-stimulated respiration was also increased (+98%) by acclimation to cold. 4. 4. FFA-stimulated respiration increased as a function of FFA concentration in both types of mitochondria. The increase in respiration due to FFA was about double in intermyofibrillar mitochondria from cold-acclimated ducklings than that of controls, but in liver mitochondria there was no increase due to cold. 5. 5. The membrane potential was estimated by the dye safranine in the absence or in the presence of FFA in the incubation medium. There were no significant differences in the basal membrane potential in the two groups and the addition of FFA led to the same depolarization in both groups. 6. 6. The significance of these alterations for acclimation to cold is discussed.

Potentiated muscular thermogenesis in cold-acclimated muscovy duckling

The capacity for nonshivering thermogenesis (NST) was examined in 26- to 27-day cold-acclimated (CA) muscovy ducklings reared for 21 days at 4 degrees C. Metabolic rate and integrated electromyographic (EMG) muscle activity were measured at ambient temperature ranging from -10 to 28 degrees C. Compared with controls reared at 30 degrees C, CA ducklings were more resistant to cold and had higher peak metabolic rate in extreme cold. Shivering threshold temperature of CA ducklings was 14.2 degrees C lower than lower critical temperature, whereas for controls the two temperatures were similar. Thus CA ducklings exhibited an NST in moderate cold. In addition, at temperatures that produced shivering, EMG activity in CA duckling muscle was lesser than that of controls, even at a higher metabolic rate. Because these ducklings are devoid of brown adipose tissue, these results indicated an increased thermogenic efficiency of muscular activity in CA ducklings.