Ultrastructural analysis of regional type II cell development within fetal and neonatal lungs

Type II cells within guinea pig lungs were studied beginning when lamellar bodies (LB) were first identifiable, to determine the pattern of their ultrastructural maturation through parturition and to search for regional differences suggested for other species in their numbers or maturity within the same lung. Fetuses were examined at gestational ages of 55, 60, and 65 days, as were newborn within 2 h of birth at 68 days. The stratified sampling system divided left lungs into nine blocks from each cranial and caudal lobe for electron-microscopic morphometry. Type II cells were compared among blocks within lobes, between lobes within age groups, and among ages for volume densities [VV(ep2, t)], numerical densities [NV(ep2, t)], and surface densities [SV(ep2, t)] per block; total tissue volumes [V(ep2)], numbers [N(ep2)], and cumulative surface areas [S(ep2)] per lung; and the VV(lb, ep2) and V(lb) of their LB. Within lobes, there were no significant differences among blocks for any parameter. Within age groups, significant interlobar differences were limited only to NV(ep2, t) (cranial greater than caudal at day 55, P less than 0.001). In age-by-age comparisons, the V(ep2), NV(ep2), and S(ep2) each increased dramatically from day 55 to 60 (P less than 0.001) but then remained unchanged through parturition. However, both VV(lb, ep2) and V(lb) increased linearly with fetal age (day 55 less than 60 less than 65 less than newborn), with VV(lb, ep2) achieving 18% type II cell volume in the postpartum group.(ABSTRACT TRUNCATED AT 250 WORDS)