Cold-induced thermogenesis in younger and older Fischer 344 rats following exercise training.

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 degrees C) and during 6 h of exposure to 6 degrees C. Rectal temperatures were recorded before and after cold exposure. NST was estimated 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 degrees C after cold exposure (36.3 +/- 0.3 vs. 31.2 +/- 0.8 degrees C). Exercise training in older animals prevented this fall from occurring (36.4 +/- 0.2 vs. 35.3 +/- 0.3 degrees 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.(ABSTRACT TRUNCATED AT 250 WORDS)