title: Somatomedin production by rat liver in organ culture. II. Studies of cartilage sulphation inhibitors released by the liver and their separation from somatomedins.
abstract: Inhibitors of cartilage sulphation have been found to be released by the rat liver in organ culture. They cause a decrease in [35S]sulphate uptake by embryonic chick cartilage and, when added to a constant amount of serum, counteract the somatomedin (SM) activity of the serum. Both of these effects are dose-dependent. Their antagonistic action, investigated in the presence of increasing concentrations of serum, appeared to resemble non-competitive inhibition which would suggest different sites of action for SM and inhibitors. Incubation of the liver explants with cortisol (0.01-1 microgram/ml) increased the sulphation-inhibiting activity of the culture medium and the effect was dose-dependent. Simultaneous addition of cycloheximide suppressed the inhibition. Gel filtration of the culture medium on Sephadex G 75 showed that: a) at pH 7.9, inhibitors eluted in the same fractions as [125I]SM-A bound to its carrier (apparent molecular weight approximately 45 000); b) at pH 2.4, inhibitors still eluted as large molecules, but SM activity appeared in the same fractions as the dissociated [125I]SM-A. The question arises whether the cartilage sulphation inhibitor might not be the same molecule as the SM-carrier protein released by the liver.
mesh_terms: D000818:Animals; D001681:Biological Assay; D002356:Cartilage / Q000378:metabolism; D002642:Chick Embryo; D002850:Chromatography, Gel; D003470:Culture Media; D003513:Cycloheximide / Q000494:pharmacology; D006854:Hydrocortisone / Q000494:pharmacology; D008099:Liver / Q000378:metabolism*; D009924:Organ Culture Techniques; D051381:Rats; D013002:Somatomedins / Q000096:biosynthesis* / Q000097:blood
chemical_list: D003470:Culture Media; D013002:Somatomedins; D003513:Cycloheximide; D006854:Hydrocortisone