Influence of increasing age on lethality induced by carbon monoxide or hypoxic hypoxia

Mice ranging in age from 2 to 150 days of age were exposed to 2,000 ppm carbon monoxide (CO) or 7.5% O2. 2-day-old mice were more resistant than older animals to the lethal effects of both CO and hypoxic hypoxia. The oldest age group (150 days) were also found to be more resistant than young adult mice to the lethal effects of both CO and hypoxic hypoxia. The role of body temperature in the age-dependent susceptibility was studied by altering the environmental temperature. Neonatal mice remained resistant to the lethal effects of CO until the environmental temperature reached 35 degrees C at which time the death rate of neonatal mice equaled that of the adult mice in 30 degrees C environment.