Immunoassay of a somatomedin-binding protein from human amniotic fluid: levels in fetal, neonatal, and adult sera.
We developed a specific RIA for a somatomedin (Sm)-binding protein, with an approximate mol wt of 35-40,000, purified from midgestational human amniotic fluid (AF) and termed AF-binding protein (AFBP). After Sephadex G-200 chromatography AFBP-RIA activity was found in fractions of fetal and cord serum only at a kav corresponding to a mol wt of +/- 40,000. Whole serum or plasma dilutions in a range of 1:20 to 1:600 showed parallelism with the standard curve. Sm-binding activity in fetal serum was found solely at a mol wt of 30-40,000; in cord serum additionally at a mol wt range of 150-200,000. AFBP serum or plasma concentrations determined by RIA were influenced by several factors: AFBP values in eight adults were highest in the morning (mean +/- SEM, 0.7 +/- 0.1 mu geq/ml) and lowest at night (0.3 +/- 0.1). AFBP values in pre- and postnatal serum showed a gradual decline with increasing age: fetal serum: mean +/- SEM, 36.7 +/- 15.7 (n = 17); adults: 0.6 +/- 0.07 mu geq/ml (n = 19). In serum from GH-deficient children AFBP concentrations were significantly higher than in an age-matched control group (P less than 0.05). Elevated values also were found in serum of children with end-stage renal failure and in serum of pregnant women at 36 weeks of gestation. AFBP was found in urine of preterm infants (mean +/- SEM, 0.04 +/- 0.005 mu geq/ml; n = 31). AFBP immunoreactivity was demonstrable in serum of three orangoutan mothers and their three children and in medium of a hepatoma cell line (PLC/PRF/5) but not in bovine, porcine, rabbit, or rat serum or in medium of cell cultures of (pre-)term placentae. We conclude that AFBP immunoreactivity is present in pre- and postnatal serum and has striking similarity to an unsaturated serum Sm-binding protein with a mol wt of +/- 40,000.
D000293:Adolescent; D000328:Adult; D000375:Aging; D000653:Amniotic Fluid / Q000032:analysis*; D000818:Animals; D002352:Carrier Proteins / Q000097:blood / Q000302:isolation & purification*; D002417:Cattle; D002648:Child; D002675:Child, Preschool; D002850:Chromatography, Gel; D002940:Circadian Rhythm; D004606:Elephants; D005260:Female; D005312:Fetal Blood / Q000032:analysis*; D005865:Gestational Age; D012739:Gonadal Steroid Hormones / Q000502:physiology; D013006:Growth Hormone / Q000172:deficiency / Q000627:therapeutic use; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D018969:Insulin-Like Growth Factor Binding Proteins; D008970:Molecular Weight; D011148:Pongo pygmaeus; D011247:Pregnancy; D011817:Rabbits; D011863:Radioimmunoassay; D051381:Rats; D013045:Species Specificity; D013552:Swine
D002352:Carrier Proteins; D012739:Gonadal Steroid Hormones; D018969:Insulin-Like Growth Factor Binding Proteins; D013006:Growth Hormone