Extraction of cartilage sulfation inhibitors and somatomedins from rat liver.

Both cartilage sulfation inhibitors and somatomedins were identified in extracts from rat liver. After extraction at pH 7.4 (neutral extract), cartilage inhibitors were found in neutral liver extracts from normal, diabetic, fasted, and hypophysectomized rats [61 +/- 4%, 68 +/- 3% 60 +/- 6%, and 62 +/- 7% below assay buffer (mean +/- SEM), respectively; all P less than 0.001 below buffer]. Exposure to 80 C or pH 2.4, inactivated the inhibitors in all samples. After gel filtration on Sephadex G-100, pH 7.4, cartilage inhibitors in the neutral extracts had molecular sizes similar to those of inhibitors in the diabetic rat serum (mol wt, greater than 45,000). After the inhibitors were removed with neutral buffer extraction, reextraction at pH 2.4 (neutral/acid extracts) revealed somatomedins only in the livers of normal rats. Cartilage stimulation by somatomedins in neutral/acid extracts was linear and parallel to stimulation by normal serum. After gel filtration on Sephadex G-75, pH 2.4, somatomedins in neutral/acid extracts from normal rat liver were found to have an apparent molecular weight larger than that of serum somatomedins (mol wt, approximately 25,000-45,000), consistent with recent findings for hepatic somatomedins. The data indicate that both somatomedins and inhibitors can be extracted from rat liver.