Dietary constituents and somatomedin activity.

Serum somatomedin activity of rats was measured under several dietary conditions by 35S incorporation into chick embryo pelvic rudiment. The mean (+/- SD) serum somatomedin activity (U/ml) was reduced following 3 days of fasting (0.41 +/- 0.12) and increased to prefasting levels in animals fed a balanced diet (0.95 +/- 0.11) for 2 days. The increase in mean somatomedin activity following 2 days of refeeding a high-protein diet (0.79 +/- 0.09) was greater than that observed with a high-carbohydrate (0.56 +/- 0.10) or a high-fat (0.60 +/- 0.10) diet, but the level was not completely restored to normal. The data confirm the previous finding that fasting reduces serum somatomedin activity and suggest that the protein content of the diet plays a major role in the restoration of serum somatomedin activity following refeeding.