Urinary trypsin inhibitor levels in amniotic fluid of normal human pregnancy: decreased levels observed at parturition.

Abstract

Urinary trypsin inhibitor, a light chain of inter-alpha-trypsin inhibitor, is reported to inhibit uterine contractility during pregnancy. The objective was to measure amniotic fluid urinary trypsin inhibitor levels in women throughout pregnancy. We determined levels of urinary trypsin inhibitor in human amniotic fluid (n = 40) by means of Western blot analysis. For quantification, computerized scanning and densitometry were used. Results were analyzed for statistical significance with the Mann-Whitney U test. During pregnancy, mean amniotic fluid urinary trypsin inhibitor levels (+/-SD) were 1.5 +/- 0.22, 1. 2 +/- 0.18, and 0.58 +/- 0.24 micromol/L at 15 to 22 (n = 10), 30 to 35 (n = 5), and 37 to 40 (n = 10) weeks' gestation, respectively. There was a significant negative correlation of urinary trypsin inhibitor level with gestational age. A significant difference was observed in amniotic fluid urinary trypsin inhibitor levels before and after (0.10 +/- 0.03 micromol/L; n = 15) the onset of labor. Amniotic fluid urinary trypsin inhibitor levels decrease significantly at term. These results support the hypothesis that parturition may occur through the down-regulation of urinary trypsin inhibitor, which may decrease uterine contractility and maintain the uterus in a state of quiescence during pregnancy.