The lecithin/sphingomyelin ratio in Macaca arctoides.
The amniotic fluid lecithin/sphingomyelin ratio (L/S ratio) of stumptail macaque monkeys (Macaca arctoides) was investigated by means of serial amniocenteses during the second half of pregnancy. Ten dated pregnancies were studied in 9 individual monkeys. The mean number of successful amniocenteses per pregnancy was 4. A rapid increase in the L/S ratio suggesting maturation of lung surfactant synthesis occurred as early as 130--140 days of pregnancy in some animals, and as late as 150--160 days in others. The earliest and latest times at which the L/S ratio first exceeded 2.0 were 135 and 164 days, respectively. These observations indicate that the L/S ratio of M. arctoides follows a course similar to that observed in human pregnancy, with a rise at 0.7--0.8 of term gestation. M. arctoides thus appears to be a useful model for the study of factors affecting fetal lung maturity, on the basis of the amniotic fluid L/S ratio. In particular, a rapid rise in L/S ratio before 130 days of pregnancy would be highly suggestive of accelerated maturation of pulmonary surfactant production.