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Abstract

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 μgeq/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 μgeq/ml (n = 19). In serum from GH-deficient children AFBP concentrations were significantly higher than in an age-matched control group (P < 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 μgeq/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.

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Copyright © 1984 by The Endocrine Society
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