1693 LABOR STIMULATES SURFACTANT SECRETION IN NEWBORN RABBIT LUNG SLICES

Abstract

We previously reported that labor increased the amount of surfactant phospholipid in newborn rabbit lung lavage but it was unclear if the effect was on synthesis or secretion. We have now examined the effect of labor on secretion in a slice model. Newborn rabbits are injected i.p. with 3H-choline and killed 4 h later. Slices from the blood-free lungs are incubated in buffer for 2.5 h. Initially the lipids secreted are similar to those of lung tissue but after 3 changes of buffer the lipids secreted are very similar to those of lung lavage. We measure the rate of secretion of 3H-phosphatidylcholine (PC) during this period. At 31 days gestation the rate of secretion increased from 198±18 cpm/h/mg tissue protein in 16 litters delivered before labor to 281±21 in 31 litters delivered after oxytocin-induced labor (P<0.02). Spontaneous labor was also stimulatory while oxytocin without labor was not. We attempted to mimic and abolish the effect of labor on PC secretion by incubating the slices with various agents. 10−5M prostaglandin E2 and 10−4M terbutaline stimulated secretion in slices from animals delivered prior to labor by 20% and 33%, respectively. Pilocarpine had no effect. 2×10−4M indomethacin and 10−4M propranolol inhibited secretion in slices from animals delivered after labor by 49% and 42%, respectively. Atropine had no effect. These data show that labor stimulates surfactant secretion and thus may be an important factor in the prevention of RDS. The effect of labor may be mediated, at least in part, by prostaglandins and catecholamines both of which increase during labor and birth. (Supported by HD-11018).