Fetal lung maturation IV: the release of phosphatidic acid phosphohydrolase and phospholipids into the human amniotic fluid.

The relationship between surface active material and phosphatidic acid phosphohydrolase (PAPase) activity was examined in human amniotic fluid after centrifugation at 105,000 X g for one hour. The distribution of PAPase activity between the pellet and supernatant fractions was similar to that of phospholipids in the amniotic fluid. The majority of the PAPase activity was found to be associated with the pellet fraction. Similarly, 82% of the phospholipid was also present in this fraction. Of the total palmitate present in the original sample, approximately 90% was found in the pellet after centrifugation. Palmitic acid constituted 75% of all fatty acids present in the phosphatidylcholine identified in the pellet. By sharp contrast only 4% of the total protein was pelletized by centrifugation. The pelletized fraction isolated from amniotic fluid after 105,000 X g centrifugation closely resembles the lamellar bodies in: (1) its phospholipid pattern; (2) palmitate concentration in phosphatidylcholine; and, (3) the presence of PAPase activity with a high specific activity. Collectively, these findings lend strong support to the concept that a lamellar-like body is released from fetal lung into the amniotic fluid.