The effect of prolonged cold exposure on heat production in new-born rabbits.

1. The rates of oxygen consumption and the colonic temperatures were monitored from birth in rabbits delivered by Caesarean section at term. The rates of oxygen consumption at 25 and 36 degrees C rose over the first 12 hr of life.2. Thirty rabbits were kept unfed in an environment of 25 degrees C from birth. Extra oxygen consumption, in response to cold exposure, failed 24-34 hr later. Twenty-four of these rabbits were allowed to recover in an environment of 36 degrees C. The metabolic response to cold exposure did not return in those kept unfed or given glucose but those fed with rabbit's milk showed significant recovery when re-exposed to cold 4 or 18 hr later.3. The tissue glyceride content of brown and white adipose tissue and the liver were greatly reduced once the animals failed to respond to cold exposure and no significant rise was detected during the recovery period after a milk feed.4. Another twelve rabbits were kept unfed in an environment of 36 degrees C. These animals showed a poor metabolic response to cold exposure after 48 hr, although their brown adipose tissue was still replete with fat and the blood glucose rose to normal values during cold exposure.5. These results suggest that an increase in oxygen consumption in response to cold exposure can occur even though brown adipose tissue is largely depleted of glyceride provided that an alternative supply of fuel is available. Glucose alone is not an adequate source of energy.