The liver as a source of somatomedin

Somatomedin (Sm) activity (measured by [35S] utake in chick embryo cartilage) was determined in serum samples simultaneously drawn from the hepatic vein, portal vein, femoral artery and demoral vein of seventeen anaesthezied normal adult dogs). A pool of human serum was taken as reference (Sm = 1 U/ml). Sm levels in the peripheral vein of dogs were 0.38 +/- 0.03 U/ml). Mean +/- SEM). Sm activity was greater in the hepatic vein (0.48 U/ml) than in the other vessels (0.36, 0.39, 0.38 U/ml), and the paired differences were significant (P less than 0.002 to P less than 0.05). In three dogs which received b-GH (20 IU/day), the Sm levels were significantly increased after nine days in the femoural vein (P less than 0.05) and in the hepatic vein (P less than 0.05). The validity of the assay is discussed; a possible interference of NEFA in the assay is eliminated. The difference of Sm levels between hepatic and portal veins, related to hepatic flow measured in seven of these dogs, indicate an important production of Sm by the liver.