TIME-COURSE OF LUNG GROWTH FOLLOWING EXPOSURE TO HYPOBARIA AND OR HYPOXIA IN RATS/

Four-week-old rats were divided into five groups: general controls, we ight-matched controls (weight matched to hypobaric hypoxia), hypobaric hypoxia, normobaric hypoxia, and hypobaric normoxia. Lung growth impa irment in weight-matched animals occurred by reduction in cell number and size, In both hypoxic groups, lung weight, RNA and protein were si gnificantly higher on day 3, and DNA on day 5 and remained higher ther eafter. Maximum H-3-TdR incorporation occurred on day 3 in both hypoxi c groups. Hypoxia increased RNA/DNA ratio on day 1 and protein/DNA on day 3. Following 3 days of recovery, DNA synthesis and RNA/DNA ratio o f hypoxic groups and controls were identical. DNA synthesis also doubl ed on day 5 in hypobaric normoxia compared to general controls. Hypoxi a up regulates lung growth despite down regulation by undernutrition. Maximum lung growth stimulation occurs during early exposure by cellul ar hypertrophy followed by hyperplasia. Low pressure by itself also st imulates lung growth. Cellular activity returns immediately to normal levels after removal of hypoxic stimulus.