Cartilage sulfation inhibitor from rat liver: partial characterization of properties and biologic action.

Abstract Cartilage sulfation (somatomedin) inhibitors (CSI) from rat liver produce reversible inhibition of cartilage growth. After gel filtration Sephadex G-200, CSI appear to have MW ∼100,000 and they are urea- and trypsin-labile factors. To explore further the mechanism of CSI action, we used the chick pelvic rudiment bioassay and studied the effect of CSI on the incorporation on 35 S-sulfate (proteoglycan synthesis), 14 C-leucine (protein synthesis), 3 H-uridine (RNA synthesis), and 3 H-thymidine (DNA synthesis). Normal rat serum (NRS) significantly stimulated the incorporation of all four isotopes, as expected. After a 24-hour incubation, CSI significantly blunted cartilage stimulation by NRS regarding total isotope uptake (1), 35 S-sulfate (NRS, 96 ± 8 mcg/100 mg cartilage dry weight; NRS + CSI, 48 ± 4, mean ± SEM, n = 29, P 14 C-leucine (NRS, 2,089 ± 172 cpm/mg dry weight; NRS + CSI, 1,102 ± 141, n = 18, P 3 H-uridine (NRS, 6,711 ± 832 cpm/mg; NRS + CSI, 3,227 ± 425 cpm/mg, n = 18, P 3 H-thymidine (NRS, 3,540 ± 620 cpm/mg; NRS + CSI 3,249 ± 285, n = 19). The inhibition of 35 S-sulfate and 14 C-leucine uptake by CSI was dose-dependent and reversible. For 35 S-sulfate, uptake by cartilage incubated with CSI alone for 40 hours was 13 ± 3 μg/100 mg; with CSI for 16 hours then fresh medium with NRS for 24 hours uptake was 39 ± 12, P 14 C-leucine, uptake with CSI alone for 40 hours was 22.8 ± 5.4 × 10 3 cpm/mg; with CSI 16 hours, then NRS 24 hours, uptake was 59.9 ± 9.3 × 10 3 , P 35 S-sulfate, 14 C-leucine, 3 H-uridine, but not 3 H-thymidine. CSI action is dose-dependent and reversible. The data suggest that CSI can exert broad antianabolic effects on normal cartilage.