THERMOGENESIS DURING REST AND EXERCISE IN COLD-AIR

Nine non-cold-acclimated subjects (5 female, 4 male, mean age 22.5 yea rs) were studied to determine whether nonshivering thermogenesis contr ibutes to cold-induced metabolic heat production during rest (50 min s tanding) and exercise (40 min treadmill walking) in 5 degrees C. Propr anolol was administered orally (females, 60 mg, 1.12 mg . kg(-1); male s, 80 mg, 0.96 mg . kg(-1)) to block nonshivering thermogenesis. Measu rements were taken at both 25 degrees C, 13.1 Torr (water vapor pressu re; 1 Torr = 133.3 Pa) and 5 degrees C, 3.6 Torr, with sessions random ly assigned to be drug-neutral (DN), drug-cold (DC), placebo-neutral ( PN), and placebo-cold (PC). Body core temperature was not different be tween any of the experimental conditions. Mean body temperature (5 deg rees C, 32.2 +/- 0.20 degrees C (+/- SEM); 25 degrees C, 35.3 +/- 0.20 degrees C) and mean skin temperature (5 degrees C, 22.4 +/- 0.70 degr ees C; 25 degrees C, 31.4 +/- 0.60 degrees C) were lower (p < 0.05) in the 5 degrees C than 25 degrees C environment (rest, exercise, drug ( D), placebo (P), combined); while shivering (EMG) was higher (16.5 +/- 3.9% above baseline) at 5 degrees C than 25 degrees C (15 +/- 2.1% be low baseline) (p < 0.05). The greater Vo(2) in 5 degrees C compared wi th 25 degrees C for the same condition is the thermoregulatory Vo(2) ( TVo(2)). TVo(2) (mL . min(-1)) was lower (p < 0.05) on the D (($) over bar X = 189.5 +/- 17.7) than on the P (($) over bar X = 238.1 +/- 20. 2) during rest and during exercise (D, 206.1 +/- 63.7; P, 338.4 +/- 46 .7). The EMG was 21% above baseline in the DC, and 12% above baseline for PC (p > 0.05). These results suggest a nonshivering component to h eat production during acute cold exposure, which can be blocked with p ropranolol.