Plasminogen activators and inhibitors in amniotic fluid

Abstract

Ten amniotic fluid samples obtained at elective caesarian section were examined for the presence of tissue-type plasminogen activator (t-PA), urokinase-type plasminogen activator (u-PA) and the two specific plasminogen activator inhibitors, PAI-1 and PAI-2. u-PA antigen was demonstrated in all samples (mean concentration equivalent to 0.35 iu/ml), but its bioactivity was very low (mean activity 0.13 iu/ml) when assessed by a bioimmuno-assay (BIA) using chromogenic substrate. None of the samples analysed by ELISA technique had measurable levels of t-PA, neither could any activity of t-PA be demonstrated by a sensitive BIA or fibrin plate technique. Significant amounts of both PAI-1 and PAI-2 antigen were present in all samples, and the mean values were 12.2 and 43.4 ng/ml, respectively. The average inhibitory capacity per ml of amniotic fluid measured by assessing the residual t-PA activity following addition of a known amount of single chain t-PA to the samples was 17.3. Thus, this study demonstrates a fibrinolytic system in amniotic fluid, which is characterised by absence of t-PA activity, low bioactivity of u-PA and excess of the two specific inhibitors, PAI-1 and PAI-2. This inhibitory capacity of amniotic fluid may play a role in preventing premature rupture of membranes.