Functional delay in lung maturation in fetuses of diabetic rabbits

Lung maturation was studied in fetuses of rabbits made diabetic with alloxan. Lung maturation was examined functionally with pressure-volume curves and by determining surfactant content of lung lavage on a surface balance, and biochemically by measuring disaturated phosphatidylcholine content (DSPC) and lecithin: sphingomyelin ratio (L/S) of lung lavage and DSPC content of lung tissue. Pressure-volume curves of 27.5-day fetuses of diabetic does demonstrated less deflation stability. Functional assessment of pulmonary lavage surfactant measured on a surface balance was less in diabetic fetuses at both 27.5 and 29.5 days of gestation. There were no differences in DSPC content or L/S of lung wash or DSPC in whole-lung tissue between diabetic and control fetuses. The discordance between surfactant function and concentrations of major surfactant phospholipids suggests that surfactant in fetuses of diabetic animals is qualitatively different from that in the normal fetus. These findings may explain why analysis of amniotic fluid phospholipid content sometimes fails to predict risk of respiratory distressed syndrome correctly in human diabetic pregnancies.