CRITICAL OXYGEN TENSIONS IN NEWBORN, YOUNG, AND ADULT MICE.

Abstract

Critical oxygen tensions of newborn, young, and adult mice are presented. At neutral environmental temperature, oxygen consumption of newborn mice is unaffected by reducing the oxygen tension of inspired air to 85 mm Hg. Five-day-old mice, at neutral environmental temperature, tolerate a decrease in ambient oxygen tension to 100 mm Hg without a depression of oxygen consumption. Adult mice behave in a qualitatively similar fashion. When the ambient temperature is lowered below neutral, the mice are unable to maintain a constant oxygen consumption if hypoxia is induced. It appears as though the depression of oxygen consumption during hypoxia is linearly related to the hypothermic increment to metabolism: the greater the extra oxygen consumption, the more readily it is reduced. Although the newborn mouse is unable to combat hypothermia effectively, it does respond to mild hypothermia for short periods by increasing its rate of oxygen consumption. Evidence is presented of a rapid maturation of temperature controlling mechanisms during growth.