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The Growth Hormone Dependence of a Somatomedin-Binding Protein in Human Serum^*

ROBERT M. WHITE, S. PETER NISSLEY, ALAN C. MOSES, MATTHEW M. RECHLER and ROGER E. JOHNSONBAUGH

Endocrine Section, Metabolism Branch, National Cancer Institute the Section on Biochemistry of Cell Regulation, Laboratory of Biochemical Pharmacology, National Institute of Arthritis, Metabolism Bethesda,Maryland 20205
Digestive Diseases National Institutes of Health Bethesda,Maryland 20205
The Division of Pediatric Endocrinology, Department of Pediatrics, National Naval Medical Center and Uniformed Services University of the Health Sciences Bethesda,Maryland 20014

Address requests for reprints to: Dr. S. Peter Nissley, Metabolism Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20205.

We previously reported that a serum somatome-din (SM)-binding protein is GH dependent in the rat. We now show that a similarly sized SM-binding protein in humans is also GH dependent. Multiplication-stimulating activity (MSA), purified from medium conditioned by the BRL-3A rat liver cell line, was radioiodinated and used as a human SM analog for these studies. A normal human serum pool and sera obtained from nine GH-deficient patients before and after GH treatment were gel filtered on Sephadex G-200 in 0.05 M NH₄HCO₃. Specifi c [^l25I]MSA-binding activity was measured in each column fraction. When pre-GH sera were gel filtered over Sephadex G-200, specific [^I25I]MSA-binding activity was low and eluted in the -globulin region (peak II), in the albumin region (peak III), or in both depending upon the patient. After GH treatment, specific [¹²⁵I]MSA binding increased dramatically and was always found primarily in peak II, resembling the pattern for normal human serum. For three patients, Sephadex G-200 column pools were chromatographed on Sephadex G-50-1 M acetic acid to dissociate and separate binding protein from SM activity. SM activity was measured by a [³H]thymidine incorporation assay in chick embryo fibroblasts and by a competitive protein-binding assay using rat serum binding protein. SM activity coeluted with specific [^l25I]MSA-binding activity on Sephadex G-200 gel filtration of normal, pre-GH, and post-GH sera and was higher in column fractions from post-GH and normal sera than from pre-GH sera. To determine whether [^l25I]MSA-binding activity measurements on Sephadex G-200 column fractions reflected the distribution of binding capacity, Scatchard analysis of MSA binding to stripped binding protein was performed on Sephadex G-200 pools that had been gel filtered on Sephadex G-50-1 M acetic acid. The maximal binding capacity was found in the Sephadex G-200 column fractions identified by the highest [¹²⁵I]MSA binding activity. Binding capacities of peak II binding protein increased several-fold after GH treatment. We conclude that the level of a -globulin-sized SM-binding protein is GH dependent in humans.

^* A preliminary report of these findings was presented at the 61st Annual Meeting of The Endocrine Society, Anaheim, CA, 1979 (Abstract 679). This work was supported in part by project CICC 8-06-1146 from the Bureau of Medicine and Surgery, Navy Department, Wash-ington, D.C. The opinions expressed herein are those of the authors and are not to be construed as reflecting the views of the Navy Department, the Naval Service at large, or the Department of Defense.

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Received November 12, 1980.

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