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A B S T R A C T The respiratory distress syndrome is believed to be due to insufficient surfactant. It is known that there is a greater incidence of the respiratory distress syndrome among infants delivered by cesarean section before labor than among those delivered after labor at the same gestational age. The purpose of this study was to determine the effect of labor on the production of pulmonary surfactant.We measured the phospholipid content of lung lavage in newborn rabbits delivered by cesarean section before labor at 29, 30, and 31 (full-term) days gestation and after oxytocin-induced labor at 31 days. We also measured the activities of pulmonary cholinephosphate cytidylyltransferase and cholinephosphotransferase, enzymes involved in the de novo synthesis of phosphatidylcholine, the major component of surfactant.There was a two-to fourfold increase in the amount of lung lavage phospholipid during the first 6 h after birth. This was not dependent upon gestational age at delivery. There was a further two-to fourfold increase in the next 18 h which was, however, dependent upon gestational age. Labor increased the amount of lavage This work was presented, in part, at the 61st Annual

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