Adaptation of Rats to Cold Air and Effects on Tissue Oxygen Consumptions

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Abstract
Six-week-old and 6-month-old rats were exposed to cold air of 5[degree][plus or minus]l[degree]C for 10 and 26 days. The O2 consumption of representative muscles, visceral tissues and brain cortex slices were detd. at 24[degree] and 37[degree] by the Warburg method. Six-week-old animals showed higher tissue O2 consumption rates after exposure to cold air; brain cortex was an exception. Percentage-wise, liver showed the greatest increase, kidney the least. The tissues of 6-month old rats showed no increase in their metabolic rates, with the exception of liver. When, after a 10-day cold exposure , 6-week old animals were allowed to sojourn at room temp. for 2 days, all tissue O2 consumptions studied were still high. When weanling rats were exposed to air of 5 [plus or minus] 1[degree]C, most died; when exposed to air of 12 + 2[degree]C for 5 days, no significantly increased tissue O2 consumptions could be observed, probably due to an insufficient severity of cold exposure. Adrenal glands of cold-exposed animals were enlarged; extent of hypertrophy was correlated with the severity of the cold-stress applied. In general, tissues from young animals respired faster than those from older ones, but those tissues which did not alter their respiratory rates in response to cold also showed no modification with age. There was some evidence that the QO2, was higher in the winter than in summer.