Fetal-Rat Surfactant At The Onset Of Air Breathing

Morphometric and biochemical measures of type II cell surfactant stores were combined to define late gestational maturation of the alveolar epithelium in its preparation for transition to air breathing. Fetal (G20, G22) and newborn (+10min) lung tissue was obtained from pathogen-free timed pregnant rats. Morphometric analyses of type II cells & their organelles was done using a stratified sample. Lamellar body (LB) fractions were obtained by sucrose density gradients & disaturated phosphatldylcholine (DSPC) was quantitated. The table gives the results of the volume fraction (Vv,%) of type II cell organelle content and the LB fraction and whole lung (WL) DSPC content. There was an increase in LB Vv from day 20 of gestation, with a parallel increase in LB DSPC. Within 10 min after birth, we found a significant increase in intracellular LB by morphologic and biochemical measures. This postnatal accumulation of intracellular surfactant could represent recycling of previously secreted phospholipid from the airspaces. Such an occurrence might supplement de novo pathways of surfactant production by newborn rat type II cells providing an additional source of surfactant flux.