Ultrastructural stereologic analysis of fetal rabbit type II alveolar epithelial cells following maternal pilocarpine treatment or fasting.

We have previously reported that subcutaneous administration of 5 mg/kg pilocarpine HCl, a muscarinic agonist, to pregnant white rabbits on days 24 through 27 of gestation results in an acceleration of fetal lung maturation. In the present study the ultrastructural differences observed within alveolar type II cells of 28-day fetuses from the pilocarpine and control groups were quantified by stereologic analysis. In addition, maturational changes occurring within the lungs of 28-day fetuses obtained from pregnant rabbits which were fasted for 7 days (days 21-28) were similarly analyzed. Stereologic analysis revealed that the fetal type II cells in the pilocarpine-treated group possessed a significantly greater volume density of lamellar inclusion bodies and rough endoplasmic reticulum and a significantly smaller volume density of glycogen than did controls. The volume density values for fetal type II cells of the fasted group were, with the exception of the Golgi apparatus, found to be intermediate between those of control and the pilocarpine-treated groups. It was also noted that a high percentage of the lamellar inclusion bodies within type II cells of the fasted group appeared morphologically abnormal, being characterized by a highly irregular outline and tightly packed lipid membranes. The results of this study substantiate and quantify our previously reported observation of accelerated maturation in pilocarpine-treated fetuses. In addition, they suggest a similar, though not as pronounced, effect of maternal fasting prior to delivery. However, the abnormal morphology of the lamellar inclusion bodies in the fasted group may reflect a qualitative change in the pulmonary surfactant produced by these fetuses.