STUDIES ON THERMOGENESIS IN COLD-ACCLIMATED BIRDS

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Abstract
Effects on oxygen consumption of continuous intravenous injection of various doses of L-noradrenaline were measured in anesthetized chickens acclimated to 1 °C for 3 months, and in controls. No effects were produced in either and it is concluded that noradrenaline is not a calorigenic mediator in cold-acclimated chickens. Liver succinoxidase and liver microsomal pyridine nucleotide-cytochrome c reductases of cold-acclimated and control sparrows were assayed, and there were no cold-induced differences. Since small cold-acclimated mammals show elevation of these liver enzyme systems, the findings indicate that the chemical basis of non-shivering thermogenesis (if this phenomenon is present at all) may involve different mechanisms in birds and mammals. Organ weights were measured, and it was found that in the sparrow, as in small rodents, the kidney and heart become enlarged in response to cold, perhaps indicating a convergent adaptation in these two diverse homoeotherms. Changes in the thickness and changes in color of the pectoral muscles which were observed in the cold-acclimated sparrows are discussed in relation to their possible roles in shivering thermogenesis.