Somatomedin production by rat liver in organ culture

Abstract

Organ cultures with livers from normal rats were used to investigate the production of somatomedins (SM) and the control of this activity by hormones. Orosomucoid was used as an indicator of liver activity and measured by radioimmunoassay in the culture media. This protein was released continuously over 6 days and a positive correlation was found between the concentrations of orosomucoid and total proteins. Cycloheximide and actinomycin suppressed the release of orosomucoid. Experiments using [3H]Leu incorporation indicated that the proteins released correspond to proteins synthesized de novo. Orosomucoid release was stimulated by insulin and cortisol and was inhibited by growth hormone [GH]. Both effects were dose-dependent. These results apparently demonstrate the validity of the technique used for studying the release of export proteins synthetized by the liver. Liver culture media significantly inhibited cartilage sulfation as estimated by [35S]sulfate incorporation in embryonic chick cartilage. Gel filtration (Sephadex G25) and ultrafiltration experiments showed that the inhibition was caused by large molecules. Heating of the media (100.degree. C for 20 min) reduced, but did not entirely suppress, the inhibitory effect. The addition of Gh (1 mU[unit]/ml) or insulin (0.25-1 mU/ml) to the culture dishes significantly increased the SM activity of the medium and a dose-dependent effect was observed with insulin. Cycloheximide suppressed the insulin-stimulated SM release. A combination of GH and insulin resulted in an additive effect. Apparently SM is synthesized by rat liver in organ culture; insulin plays an important role in SM generation, as it is capable of both stimulating the SM release and amplifying the stimulatory effect of GH.