Somatomedin and Nutrition. IV. Regulation of Somatomedin Activity and Growth Cartilage Activity by Quantity and Composition of Diet in Rats*

Publisher Website
Google Scholar
Abstract
To examine the relation of somatomedin to nutritional status, bioassayable serum somatomedin activity and growth cartilage activity (SO4 uptake in vitro) were determined in rats fasted for 3 days and then either fasted for a 4th day or refed with diets varying in quantity and nutrient composition. Animals refed for 6 or 12 h had modest increases in somatomedin activity and cartilage SO4 uptake which persisted after food was withdrawn and weight loss had begun. Refeeding for 24 h produced greater increases in somatomedin activity and cartilage SO4 uptake; this model was used to study the effects of alterations in the diet. Refeeding with different quantities of a balanced diet produced dose-response increases in somatomedin activity and cartilage SO4 uptake. In animals refed isocalorically, diets of fat and carbohydrate or fat alone led to increases in somatomedin activity comparable to those with a balanced diet, yet little increase in cartilage SO4 uptake. In contrast, diets of protein and carbohydrate or protein alone led to smaller increases in somatomedin activity with greater increases in cartilage SO4 uptake (P < 0.05). Diets of fat and protein or carbohydrate alone produced intermediate responses. Although 24-h refeeding with protein-deficient diets produced an increase in somatomedin activity, continuation of refeeding to 48 h led to a decrease in somatomedin activity (P < 0.05) with cartilage SO4 uptake comparable to fasting levels. A similar decrease in somatomedin activity with low cartilage SO4 uptake was found in animals fed for 4 days with a protein-deficient diet. Serum somatomedin activity and growth cartilage activity may be determined by both quantity and nutritional composition of the diet. Dietary protein may be of particular importance, as deficiency of this constituent appears to lead acutely to a decrease in growth cartilage activity and chronically to decreases in both serum somatomedin activity and growth cartilage activity.