Development of the pulmonary airways in the fetal rat and its relation to the prenatal environment.

We studied the left lung using multi-focus microphotography in 378 rat fetuses, assessing airway branching from day 13 to day 19 of gestation, and lung growth variables from day 13 to day 21. Longitudinal growth, and monopodial and dichotomous branching brought about a consistent airway pattern with variations within each day of gestation and a small overlap between adjacent days. Amniotic fluid weight and pole to pole (PTP) distance of the lung increased quadratically with age, while fetal weight and the peripheral airway count (PAC) increased exponentially. The location of the fetus within the uterus had no effect on fetal variables, but correlations were found between maternal weight gain and both fetal weight and PTP. Fetal weight was the best predictor of PAC from gestational ages 15 to 19 days (P < 0.008). The method described allows for observations that are reproducible within the environmental variations present in normal gestation and can be used to study the effect of external factors on lung development.