METABOLISM DURING NORMOXIA, HYPEROXIA, AND RECOVERY IN NEWBORN RATS

Aerobic metabolism (oxygen consumption, V(O2), and carbon dioxide production, V(CO2)) has been measured in newborn rats at 2 days of age during normoxia, 30 min of hyperoxia (100% O2) and an additional 30 min of recovery in normoxia at ambient temperatures of 35-degrees-C (thermoneutrality) or 30-degrees-C. In normoxia, at 30-degrees-C V(O2) was higher than at 35-degrees-C. With hyperoxia, V(O2), increased in all cases, but more so at 30-degrees-C (+20%) than at 35-degrees-C (+9%). Upon return to normoxia, metabolism readily returned to the prehyperoxic value. The results support the concept that the normoxic metabolic rate of the newborn can be limited by the availability of oxygen. At temperatures below thermoneutrality the higher metabolic needs aggravate the limitation in oxygen availability, and the positive effects of hyperoxia on V(O2) are therefore more apparent.