Failure of endotoxin to cross the chorioamniotic membranes in vitro.

We have previously reported the detection of endotoxin in the amniotic fluid of patients with gram-negative intra-amniotic infection. Endotoxin or lipopolysaccharide (LPS) is a potent biologic product capable of inducing prostaglandin release from several cell types, and therefore may be involved in the onset of human parturition in the setting of intra-amniotic infection. The experiments outlined in this report were designed to determine whether endotoxin crosses chorioamniotic membranes in vitro. Chorioamniotic membranes obtained at the time of elective cesarean section were placed in Ussing chambers used for transport experiments. Endotoxin was placed in one chamber, and serial timed samples were taken from both chambers for endotoxin quantification, which was performed with the limulus amebocyte gel clot assay. Blue dextran was used to exclude the presence of large defects. Bromophenol blue was used to demonstrate membrane permeability to low-molecular weight substances. Endotoxin failed to cross the chorioamniotic membranes in all experiments (n = 11).