METABOLISM AND VENTILATION IN HYPOXIC RATS - EFFECT OF BODY-MASS

Oxygen consumption (V-O2) and carbon dioxide production (V-CO2) were measured by the flow-through method, and ventilation (VE) by the barometric technique in post-weaning age rats of 50, 100, 250 and 400 g, (5 males and 5 females in each group), at ambient temperature similar or equal to 24 degrees C. In normoxia, V-O2, V-CO2 and VE decreased with the increase in body weight (BW), whether normalization was by BW or by BW minus the weights of fat and skeleton; VE/V-O2 and rectal temperature remained constant. In hypoxia (10% inspired O-2), VE/V-O2 increased in all groups, to 2-2.5 times the normoxic values, because of a significant increase in VE (hyperpnea) and decrease in V-O2 (hypometabolism); arterial P-CO2, measured in some 100 g and 400 g rats, dropped similarly. However, the hyperpnea was about twice as large, and metabolism and body temperature decreased significantly less, in the 400 g than in the 50 g rats. The cost (ml O-2) of breathing, computed in the paralysed animal artificially ventilated, averaged similar to 0.7% (normoxia) and 2% of V-O2 (hypoxia), with no systematic differences with BW. The results agree with the concept that the metabolic response to hypoxia can be an important determinant of the magnitude of the hyperpnea.