Journal of Applied Physiology, Vol 77, Issue 6 2709-2719, Copyright © 1994 by American Physiological Society
Comparative age-related acute and chronic pulmonary oxygen tolerance in rats
S. Laudert, D. W. Thibeault, M. M. Rezaiekhaligh, S. M. Mabry and M. Huntrakoon
University of Missouri-Kansas City School of Medicine, Children's Mercy Hospital 64108.
Young rats are thought to be more tolerant to hyperoxia. We propose that
this may not be proven and depends on how tolerance is defined. We assessed
oxygen tolerance in Sprague-Dawley rats from birth to maturity by comparing
survival, lung water, antioxidant enzyme activity, lung morphometrics,
heart weight, and arterial blood gases in newborn and 27-, 44-, 48-, and
96-day-old rats exposed to 100% O2 or room air for 22 days. Some 96-day-old
rats (rest group) received only 50% O2 between 48 and 72 h. Mortality after
5 days of O2 was 0% in newborn and 27-day-old rats and 27% in 44-day-old
rats but was > 80% in 48- and 96-day-old rats. Between 5 and 22 days,
the death rate was 100% in newborns, 25% in 27-day-old rats, and 0% in 44-
to 96-day-old rats. Death occurred when lung water was > 84% except in
newborns, which tolerated high lung water for the first 7 days. In
chronically exposed 44- and 96-day-old rats, lung water returned to normal.
Enzyme activity increased with O2 at all ages but did not relate to
survival. In 96-day-old rats, the initial increase was suppressed on day 3.
All chronically O2-exposed rats had minimal nonvascular parenchymal changes
but developed right ventricular hypertrophy and increased alveolar ductal
artery muscularization and lost alveolar capillaries. The most mature rats
were least affected. In O2, there was pulmonary insufficiency the first 3
days, followed by recovery, and later hypercarbia and decreased arterial
PO2. We conclude that young rats, 0-44 days old, are more O2 tolerant for 5
days. More mature animals, surviving 5 days, are more tolerant to chronic
exposure.
