Hypercapnia-induced thermoregulatory disturbances in rabbits at low ambient temperature

The effect of 30 minute inhalation of a gaseous mixture containing 6% CO2, 21% O2 and 73 N2 on the thermoregulatory reactions was studied in rabbits at ambient temperatures (Ta) of 6 and 18 degrees C. At Ta 6 degrees C the CO2 inhalation caused a greater fall of the rectal temperature (Tre) as well as the subcutaneous and skin temperatures (TS1 and TS2) than at Ta 18 degrees C. At the same time, the gradients Tre-TS1 and TS1-TS2 decreased, the respiratory rate increased and the electrical activity of skeletal muscles was depressed in both thermal conditions. A considerable fall in heat production occurred only at Ta 6 degrees C, at which the initial electric activity of the skeletal muscles was also greater. These results suggest that Tre fall associated with CO2 inhalation at low temperatures was caused mainly by inhibition of shivering-thermogenesis, however, the changes in skin temperatures were without any greater importance for the body temperature at Ta 6 degrees C as well as at 18 degrees C.