Effects of insulin and multiplication-stimulating activity on proteoglycan biosynthesis in chondrocytes from the Swarm rat chondrosarcoma.

Somatomedins have been consistently reported to be more potent than insulin in stimulating proteoglycan synthesis and other anabolic responses in cartilage tissue, and pharmacologic levels of insulin have been required for significant effect. Multiplication-stimulating activity (MSA), purified from medium conditioned by a rat liver cell line, and insulin were tested on monolayer cultures of chondrocytes derived from the Swarm rat chondrosarcoma for their ability to stimulate proteoglycan synthesis. MSA at a concentration of 500 ng/ml in serum-free Dulbecco’s modified Eagle’s medium stimulated proteoglycan synthesis to approximately two-thirds of the level achieved with 15% fetal calf serum. The concentration required for half-maximal effect was 100 ng/ml. Insulin (10 ng/ml), on the other hand, not only stimulated [3sS]sulfate incorporation to higher levels than MSA, but a half-maximal effect was obtained at the physiolugic concentration of 1 ng/ml. Kinetic experiments indicated that incorporation of radioactivity was dependent on the length of time of exposure of the chondrocytes to the two hormones in the culture medium. Stimulation of [3sS]s~lfate incorporation reflected real increases in proteoglycan synthesis since chemical analyses showed increases in the accumulation of macromolecules which contain hexuronic acid and hexosamine in MSA and insulin maintained cultures. MSA and insulin also stimulated the incorporation of [‘Hlserine, [‘Hlproline, and [‘H]glucosamine into macromolecules. The increase in incorporation of radioactivity was not due to a mitogenic response by the chondrocyte to either of the two hormones.