[Origin of low molecular weight protein in amniotic fluid]

This study was designed to clarify the origin of some low molecular weight (M.W.) proteins in amniotic fluid. Fragments of amniotic membrane were incubated in Krebs solution for six hours. During the incubation period, 2 ml samples of solution were collected at 5, 15, 30, 60, 120, 180, 360 minutes. The protein concentration of samples was measured with a LASER"NEPHELOMETER. The protein concentration increased significantly from 1.25 +/- 0.21 mg/g.w.w. at 60 minutes to 2.33 +/- 0.67 mg/g.w.w. of amniotic membrane at 360 minutes (p less than 0.001). Samples were also analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Proteins of M.W. less than 56 X 10(3) formed several bands, including band 15 (M.W. = 38 X 10(3)), bands 18-19 (M.W. = 23-25 X 10(3)) and band 21-23 (M.W. = 13-19 X 10(3)). Neonatal saliva and urine were also analyzed by SDS-PAGE. The saliva contained proteins of bands 15 and 20 (M.W. = 22 X 10(3)), and the urine a protein of band 14-15 (M.W. = 38-45 X 10(3)). Although the protein of band 20 was the greatest percentage of total protein in saliva samples, it could not be detected in amniotic fluid. Therefore, saliva was probably not a source of low M.W. proteins in amniotic fluid. Amniotic fluid proteins of band 15 probably originated from fetal urine. And proteins of band 21-23 were probably synthesized by the amniotic membrane.