Adaptive changes in cats after long-term exposure to various temperatures.

Two groups of cats were exposed to 5 and 30 degrees C, respectively for 24 mo in climatic chambers under artificial illumination. Then the ambient temperatures were reversed for both groups for another 36 mo. The group adapted to cold for 36 mo showed an increase in fur growth (+35%), an increase in resting metabolism (+20%), and a shift in threshold of the cold-induced metabolic response to 8 degrees C lower ambient temperatures. Norepinephrine (0.4 mg . kg-1) elicited nonshivering thermogenesis (+37%) in the cold-adapted animals but was ineffective in the warm-adapted ones. Fur insulation at thermoneutrality was 55% higher in the cold-adapted cats. During acute exposure to -5 degrees C, tissue insulation decreased in both groups; fur insulation increased by 34% in the warm-adapted cats but remained nearly constant in the cold-adapted animals. At all ambient temperatures cold-adapted cats had higher (+0.4 degrees C) rectal temperatures. Body weight was not significantly different in both groups, although the cats living in the cold had a 45% higher metabolism. This was compensated by an increased food consumption.