[Movement of plasma leu-enkephalin-like substance concentrations during pregnancy]

By the use of high performance liquid chromatography and a specific radioimmunoassay method combined with a new dialysis technique, plasma levels of leu-enkephalin were determined in 26 women who had become pregnant normally, some of whom were in 5 to 40 weeks gestation and the others were 3 days postpartum. Leu-enkephalin-like immunoactivity rose during 5-6 weeks gestation (982.0 +/- 388.3pg.ml-1) and 3 days after delivery (594.4 +/- 289.2pg.ml-1). This pattern differed significantly from that of the normal adult control groups (174.9 +/- 75.3pg.ml-1). The concentrations of serum leu-enkephalin during 10-40 weeks of gestation were within normal limits. These results indicate that the serum leu-enkephalin concentrations increase in the early stage of pregnancy. Whereas the physiological mechanism and exact meaning of this change are still unknown, the results strongly suggest that this substance has an important part to play in such physiological functions as pregnancy.