Somatomedin Peptide Distribution and Somatomedin-Binding Protein Content in Cord Plasma: Comparison to Normal and Hypopituitary Plasma*

Publisher Website
Google Scholar
Abstract
To characterize the macromolecular forms of somatomedin (SM) in human newborn plasma, the MW distribution of endogenous SM peptides was studied as well as the content and distribution of the acid-stable and the unsaturated SM-binding proteins (SMBP) in cord blood from 13 normal term infants. The radioreceptor assayable SM peptide content was significantly reduced in newborns compared with that in normal adults. Furthermore, 50% of the SM content of newborns circulated as part of 50,000 MW complex, in contrast to adult plasma where the majority of SM peptide content is found in 150,000 MW range. Unsaturated SMBP was strikingly elevated in newborns (mean .+-. SEM [standard error of the mean], 2.75 .+-. 1.73 U/ml) compared to adult values of 0.63 .+-. 0.24. Sephacryl-200 chromatography demonstrated that the unsaturated SMBP is found in the 40,000-50,000 MW region in newborns, adults and [growth hormone]-deficient children, although adults appear to have secondary peak of unsaturated SMBP in the 150,000 MW region. Assay of the acid-stable SMBP indicated similar levels in newborns (1.15 .+-. 0.26 U/ml) and adults (1.18 .+-. 0.47) and strikingly lower values in GH-deficient subjects. The MW of the acid-stable SMBP of newborns, adults, and hypopituitary dwarfs appeared similar, measuring approximately 60,000. Depsite low levels of SM peptides, human cord plasma contains normal levels of the acid-stable SMBP and elevated levels of the unsaturated SMBP. The role of these binding proteins in cord plasma remains uncertain, but suggests that other SM peptides may be important in fetal growth.