Regulation of Mammalian Growth in Cold Environments: Studies of DNA Synthesis in Rattus norvegicus

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Abstract
Short-term cold exposure (7°C) of warm acclimated (24°C) laboratory rats had no effect on in vivo synthesis of deoxyribonucleic acid (DNA) (as reflected by incorporation of intraperitoneally injected tritiated thymidine [3H-thymidine] into DNA) in liver and small intestine. Short-term cold exposure increased DNA synthesis in brown adipose tissue and concomitantly depressed DNA synthesis in skeletal muscle. DNA synthesis in brown adipose tissue of long-term cold acclimated (7°C) rats exposed to either 7° or 24°C was depressed relative to that of warm acclimated rats exposed to 7°C, but was slightly greater than that of warm acclimated rats exposed to 24°C. Cold acclimation depressed DNA synthesis in skeletal muscle of rats exposed to either 7° or 24°C. These results show that although exposure of a mammal to cold causes increased growth of brown adipose tissue, it causes decreased growth of skeletal muscle. The functional significance of the results is discussed in relation to mammalian energetics in cold environments.

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