OXYGEN CONSUMPTIONS OF HYPOTHERMIC RATS AND ACCLIMATIZATION TO COLD

Abstract

Heat production of rats while cooled to near lethal temps. and subsequently rewarmed, was estimated from oxygen consumption. The latter was observed continuously by photo-graphically recording the oxygen pressures (on Pauling analyzer) of effluent air flowing past a rat enclosed in a cylinder. When the cylinder was in cool water the rat''s colonic temperature, measured by thermocouples, decreased. The heat production accelerated 2- to 2.5-fold at first; this acceleration could be prevented by deep anesthesia or by passing 7% oxygen to the rat. Later the consumption diminished, extrapolating to zero at colonic temp. of 15[degree]C. During rewarming the consumption at each colonic temp. was less than during cooling. Rats were often able to rewarm themselves without the aid of heat conducted from the environment. Heat deficits and rates of net heat losses or gains were estimated from increments of colonic temp. The pulse frequency, read from ecg''s., increased at the beginning of cooling only 15% above that of the warm rat; thereafter it de-clined as colonic temp. decreased. Acclimatization to cold was demonstrated in the increases of resting oxygen consumption found after rats lived in air of 5[degree]C for 5 days or more. At the same time no modification was found in maximal rate of oxygen consumption, or in decrement of colonic temp., or in lower limit (15[degree]C) of lethal core temp.