The inability of old rats to maintain body temperature during cold exposure has been well documented. This study evaluated the effect of exercise on the rates of cold-induced O2 consumption and the contribution of nonshivering thermogenesis (NST) to these rates. Younger (12 mo) and older (24 mo) male Fischer 344 (F344) rats were divided into exercised and sedentary groups. Exercised rats were run on a motor-driven treadmill 60 min/day, at 19-24 m/min, 5 days/wk for 6 mo. At the conclusion of the 6-mo training period, O2 consumption of all four groups was measured at thermoneutrality (26°C) and during 6 h of exposure to 6°C. Rectal temperatures were recorded before and after cold exposure. NST was esimated from the ability of isolated brown fat mitochondria to bind guanosine 5'-diphosphate (GDP). Core temperature of older sedentary rats fell 5.1 ± 0.4°C after cold exposure (36.3 ± 0.3 vs. 31.2 ± 0.8°C). Exercise training in older animals prevented this fall from occurring (36.4 ± 0.2 vs. 35.3 ± 0.3°C). Core temperatures of cold-exposed younger exercised and sedentary rats did not differ from thermoneutral values. Exercise did not alter the rates of resting body mass-independent (ml·min-1·kg body mass-0.67) O2 consumption in younger or older rats. However, body mass-independent and lean body mass (LBM)-independent (ml·min-1·g LBM-0.67) cold-induced O2 consumptions of older exercised rats were significantly elevated relative to those of older sedentary animals. This effect of exercise was not seen in younger rats. No significant differences in the binding of GDP to isolated brown fat mitochondria were observed, indicating that exercise or aging did not affect the rat's NST capacity. These data are consistent with the hypothesis that the protective effect of exercise training on cold-induced hypothermia in older rats primarily reflects increased shivering rather than NST. Furthermore, our data suggest that the fall in core temperature of older F344 rats may reflect, to a large degree, the sedentary life style of the animal.
|Original language||English (US)|
|Journal||American Journal of Physiology - Regulatory Integrative and Comparative Physiology|
|State||Published - 1988|
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