Effects of medium composition and metabolic inhibitors on glycosaminoglycan synthesis in chick embryo cartilage and its stimulation by serum and triiodothyronine

Incorporation of inorganic sulfate into glycosaminoglycans of chick embryo sternum is stimulated by serum and triiodothyronine. Variations in the amino acid content of the medium, and in particular in the concentration of glutamine, changed the incorporation in control and stimulated sterna to the same degree. Omission of Na⁺ from the medium greatly reduced incorporation in both control and stimulated sterna; incorporation, and its stimulation by triiodothyronine, was restored by raising the concentration of Na⁺. Ouabain and valinomycin inhibited incorporation more than 90%, and triiodothyronine did not stimulate under these conditions. Puromycin and cycloheximide also inhibited incorporation almost completely, and abolished the stimulation by triiodothyronine and serum. Addition of p-nitrophenyl-β-xyloside, in the presence of puromycin or cycloheximide, restored sulfation to a level of 5–10% of the control value; however, this level of incorporation was not increased by addition of serum or triiodothyronine.Actinomycin D, colchicine and vinblastine inhibited incorporation by 40% or less at the highest concentrations tested; however, these three agents completely abolished the ability of triiodothyronine to stimulate incorporation. Lumicolchicine and cytochalasin B decreased incorporation in controls slightly, but did not affect the stimulation by serum or triiodothyronine.The results indicate that thyroid hormones stimulate glycosaminoglycan synthesis only under conditions which support efficient synthesis in control incubations, and suggest that microtubule formation may be essential to the mode of action of thyroid hormones in this system.