The Effect of Quantity and Nutritional Quality of Dietary Proteins on Plasma Concentration of Insulin-Like Growth Factor Binding Proteins (IGFBP) and the Saturability of IGFBP with Endogenous IGF-I
Plasma concentrations of insulin-like growth factor-I (IGF-I) have been shown to be controlled by growth hormone, insulin and nutritional status of animals.1–3 In previous papers, the present authors demonstrated that quantity and nutritional quality of dietary proteins significantly affect the plasma concentration of IGF-I.4 The concentration correlated well with the growth rate or the rate of whole body protein synthesis.5 We also showed that liver content of IGF-I mRNA was also strongly affected by the status of protein nutrition.6 7 It decreased greatly under protein deprivation and it was highly correlated with the plasma IGF-I concentration. The content of the mRNA species of larger molecular weight was most severely affected. These results strongly suggest that the rate of body protein synthesis or growth rate is regulated by the plasma concentration of IGF-I through liver IGF-I mRNA content (or the rate of synthesis and secretion of IGF-I by liver).
KeywordsCasein Diet Isolate Soybean Protein Fractional Synthesis Rate Acid Labile Subunit Ligand Blotting
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