Maturation of the fetal lung. I. Phosphatidic acid phosphohydrolase in the fetal and newborn rat.

Phosphatidic acid phosphohydrolase (PAPase) activity was measured in the lungs, brain, liver and kidneys of fetal, newborn and adult rats. The highest activity was found in the kidneys. In one-day-old rats pulmonary enzyme activity was nearly as high as in the renal tissue. In four-days-old rats the highest activity was found in the 10% homogenate of the lung, the highest PAPase specific activity could be demonstrated in the mitochondria. In the fetal lung, the enzyme activity moderately increases from the 18th day of gestation up to birth; at birth 39-77% of the normal adult value was measured. Immediately after birth 150% activity is attained, thereafter a slow decrease can be shown throughout the first week of life but the values remain above the average adult value.