Partial characterization of somatomedin bioactivity in term human amniotic fluid

Somatomedin (SM) activity in human amniotic fluid (AF) was partially characterized. Aliquots of pooled AF, obtained at term gestation, were acidified to pH 2.3 and sequentially studied by ultrafiltration on various membranes, Sephadex gel filtration, and starch gel electrophoresis (SGE). SM activity was measured by a rat cartilage bioassay. SM activity in AF, under these conditions, was present in several stable indicated molecular size (IMS) forms; large (greater than 45,000) and small (near 10,000). The small SM was found in basic and acidic forms after SGE. These studies suggest that SM activity in term human AF is somewhat similar to SM in unextracted plasma. In addition, immunoreactive GH and insulin were measured in AF but at lower concentrations than usually found in plasma. After chromatography of AF, GH was found in large and small IMS forms, whereas most of the insulin was found in the monomer insulin IMS area.