Fetal lung maturation: human amniotic fluid phosphatidate phosphohydrolase activity through normal gestation and its relation to the lecithin/sphingomyelin ratio.

In order to evaluate the relationship between the increase in amniotic fluid phosphatidate phosphohydrolase (PAPase) specific activity and the increase in the lecithin/sphingomyelin (L/S) ratio during normal human pregnancy, PAPase specific activity and the L/S ratio were measured in 171 amniotic fluid samples obtained from 164 women who were at 17 to 42 weeks' gestation. The increase in PAPase specific activity in amniotic fluid is parallel to the increase in the L/S ratio. The correlation between PAPase specific activity and the L/S ratio in amniotic fluid from all gestational ages is highly significant. The relationship of PAPase specific activity in amniotic fluid to PAPase specific activity in gastric fluid was investigated in a study of 97 newborn infants. A highly significant correlation was found between these two values. To ascertain if a relationship exists between the specific activity of PAPase in amniotic fluid and the subsequent development of hyaline membrane disease (HMD), 223 neonates who were delivered within 72 hours of amniotic fluid collection were studied. Only one infant developed HMD out of 170 with amniotic fluid PAPase specific activity equal to or greater than 50 nmoles of orthophosphate released X mg.-1 of protein X hr.-1. On the other hand, the finding of an amniotic fluid PAPase specific activity of less than 50 nmoles was of little value in predicting lung immaturity. We believe that these findings are also supportive of the view that PAPase and surfactant are released from the type II pneumocyte as a closely related structural unit, viz., the lamellar body.