Metabolic regulation of somatomedin activity in rat liver

We have compared circulating and hepatic somatomedin (SM) activity in rats with diabetes or malnutrition of varying severity. Somatomedin activity was measured by the hypophysectomized rat costal cartilage bioassay. In both moderate diabetes and moderate malnutrition, mean serum SM activity was not significantly lower than normal (79 +/- 13% (S.E.M.) and 95 +/- 11% vs normal controls respectively). In contrast, liver perfusate SM activity was significantly reduced in both groups (51 +/- 12% for moderate diabetes and 44 +/- 12% for moderate malnutrition). Liver extract SM activity was also significantly decreased in both moderate diabetes and malnutrition (74 +/- 4% and 75 +/- 6% vs normal controls respectively). In severe diabetes and malnutrition, both liver and serum activities were low, consistent with previous reports. Our studies showed that liver SM activity fell in response to metabolic stress before a decrease in circulating levels occurred, supporting the concept that the liver regulates serum SM activity and growth in diabetes and malnutrition.