Fetal rhesus monkey lung development: lobar differences and discordances between stability and distensibility

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Abstract
Sixteen fetal rhesus monkeys, between 111 days gestation and term (165 days), underwent quasi-static pressure-volume studies of their lungs. An abrupt increase in deflation stability and pulmonary distensibility occurred between 140-150 days'' gestation. The change in pulmonary distensibility lagged approximately 10 days behind the increase in deflation stability. Before 150 days, cephalad lobes were more distensible and held more air during deflation than caudad lobes; after 150 days, caudad lobes were more distensible. [14C]Phosphatidylcholine production per mg lung per h from [14C]choline, i.e., the apparent rate of the choline pathway, also showed an increase between 140-150 days'' gestation, when surface tension lowering material was demonstrable in lung extracts. Increases in the activities of the 3 enzymes of the choline pathway (choline kinase, cholinephosphate cytidylyltransferase, and cholinephosphotransferase) did not accompany lung development. Lobar comparison of [14C]phosphatidylcholine biosynthesis revealed that the cephalad lobes showed greater choline incorporation than caudad lobes by 40% on the average. Morphological changes consisting of thinning of air space walls and proliferation of capillaries accompanied the increase in pulmonary distensibility. The discordance between the development of deflation stability, lung distensibility and morphological changes, and differences between lobes suggest that specific pulmonary developmental changes appear in different anatomical locations at differing times in gestation.