Phagocytosis and onset of human labor.

An in vitro experimental model has been developed which allows the study of amnion lysosomal enzyme release under controlled conditions. Briefly, a layer of human amnion membrane mounted on a specially designed reaction vessel serves as the reaction surface. We have noted that the addition of particulate material to these membranes incubating in pseudoamniotic fluid results in an increased release of the lysosomal marker enzyme N-acetylglucosaminidase when compared to the release in the absence of particles. This release is completely inhibited by iodoacetate and slightly by azide. A similar increased release is also noted with the use of term amniotic fluid as incubation medium when compared to centrifuged (30,000 g/20 min) amniotic fluid. Lecithin and lysolecithin were effective in releasing increasing amounts of enzyme. This increased release was noted only from membranes of placentas collected from subjects who had undergone cesarean section prior to labor. Membranes collected from vaginal deliveries after labor showed a baseline increased release but no further stimulation upon the addition of any of the substances. These results suggest that the release of lysosomal enzymes from amnion membranes is brought about by substance(s) present in amniotic fluid. Very probably, these are surfactants. The interaction of these substances with amnion cells would eventually result in an exponential burst of prostaglandin synthesis, which would result in labor.