Multiplication-stimulating activity, a family of insulin-like growth factors previously identified in medium conditioned by the BRL-3A rat liver cell line, is also synthesized by third passage cultures of rat embryo fibroblasts (REFs) maintained in serum-free medium. Conditioned serum-free medium from REFs was chromatographed on Sephadex G-75 in 1 m acetic acid, and fractions in the size range of BRL-MSA contained MSA immunoreactivity. A dose-response curve of pooled G-75 fractions was parallel to BRL-MSA standard, and levels in the REF-conditioned medium were 0.5-1 microgram/ml. REF-MSA from the Sephadex G-75 pool was equipotent to BRL-MSA in stimulating [3H]thymidine incorporation into DNA in chick embryo fibroblasts and in stimulating DNA synthesis in REFs, as measured by autoradiography. In receptor binding assays using REFs, chick embryo fibroblasts, Swarm rat chondrosarcoma cells, and rat liver membranes, REF MSA was equal to BRL MSA in competition for binding of [125I]iodo-MSA. REF MSA also behaved identically to BRL MSA in a competitive binding protein assay using binding proteins in rat serum. Further characterization of REF MSA using Bio-Gel P-10 chromatography, followed by high pressure liquid chromatography or polyacrylamide gel electrophoresis, indicated that immunoreactive polypeptides in the fibroblast medium corresponded to BRL MSA II (mol wt, 8700) and BRL MSA III (mol wt, 7100). The amount of REF MSA released into the medium increased linearly over time. Cycloheximide decreased the amount of MSA in the medium, and during a recovery period, the amount of MSA returned nearly to control levels. In summary, rat embryo fibroblasts synthesize MSA which is biologically, immunologically, and chemically identical to MSA produced by the BRL-3A rat liver cell line.

Synthesis of multiplication-stimulating activity (rat insulin-like growth factor II) by rat embryo fibroblasts.

Low somatomedin activity in cord serum from infants with intrauterine growth retardation

Immunoreactive somatomedin A (SMA) was determined in rat serum collected at 20 days of gestation and at 5, 15, 25, and 50 days of postnatal age. Adult levels were shown to be GH dependent. A rapid rise in immunoreactive SMA was observed after 15 days of postnatal age, and this was attributed to the triggering of the SMA-GH regulatory system by nutritional factors at weaning. Circulating levels of immunoreactive SMA were reduced during early development and in pregnancy, raising the possibility that early growth is regulated by an embryonic form of SM which is not detected by the SMA RIA.

Serum levels of immunoreactive somatomedin A in the rat: some developmental aspects.

Primary structure of somatomedin B: a growth hormone-dependent serum factor with protease inhibiting activity.

Somatomedins, detectable by sulfation factor activity (SFA) and/or somatomedin-like receptor activity (SmLRA), were measured in the serum of 72 normal fetal lambs of varying gestational ages and in 12 fetuses before and after hypophysectomy. Three hypophysectomized fetal lambs were infused with GH and/or insulin. Three intact fetal lambs were infused with glucose. Parturition was induced by infusion of synthetic ACTH into 5 fetal lambs. SmLRA and SFA were compared to a pool of adult sheep serum arbitrarily designated 1.00 U/ml. Serum SmLRA correlated significantly with gestational age (r = 0.65; P P > 0.05). Serum SmLRA and SFA were unchanged by hypophysectomy of the fetus and GH infusion but were reduced by insulin infusion. Plasma SmLRA correlated negatively with plasma insulin during glucose infusion (r = -0.67; P < 0.05). ...

Serum Somatomedin Activity after Hypophysectomy and during Parturition in Fetal Lambs

Somatomedin A by radioreceptor assay and somatomedin B by radioimmunoassay were measured in serum from women immediately after parturition and from their newborns. The mean levels of somatomedin A in both mothers (0.54 U/ml) and infants (0.50 U/ml) were significantly decreased compared to a reference group consisting of 21 non-pregnant women (0.91 U/ml). There was no difference between the mothers and their children. The mean somatomedin B value in serum from the mothers (63.9 microgram/ml) was above that found in non-pregnant women (19.2 microgram/ml) and the mean value in cord blood and serum from the infants (7.1 microgram/ml) was below it. A positive correlation was noted between somatomedin A and B in cord blood; r = 0.78. The combined somatomedin A and B values in cord blood were positively correlated to birth weight (r = 0.51, P less than 0.05).

Somatomedin A and B in serum from neonates, their mothers and cord blood.

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Somatomedin A and B in serum from neonates, their mothers and cord blood.