Somatomedin C in protein and amino acid nutrition

生长激素C（或胰岛素样生长因子- i， IGF-I）是一种肽激素，其结构已知与胰岛素相似。然而，igf - 1表现出不同于胰岛素的生物学特性。igf - 1主要在动物生长激素和营养状况的控制下由肝脏产生。然而，膳食蛋白质的作用尚未得到广泛研究。本研究旨在阐明膳食蛋白质对血浆免疫反应性（ir） IGF-I浓度的影响，IGF-I与血浆IGF-I结合蛋白的关联模式，以及血浆ir-IGF-I浓度与全身蛋白质合成速率的相关性。膳食蛋白质的营养质量对血浆ir-IGF-I有广泛的影响。饲喂酪蛋白饮食的大鼠的ir-IGF-I浓度最高，而饲喂无蛋白饮食的大鼠的ir-IGF-I浓度最低。饲喂谷蛋白或玉米谷蛋白的大鼠血浆ir-IGF-I呈中间值。在谷蛋白饲粮中添加赖氨酸和苏氨酸或在玉米谷蛋白饲粮中添加色氨酸和赖氨酸可显著提高血浆中ir-IGF-I浓度。膳食蛋白质的营养价值也影响igf - 1与igf结合蛋白的结合模式。饲喂酪蛋白日粮的大鼠血浆中igf - 1主要存在于150kda部分。然而，在给予无蛋白质饮食的大鼠中，在这部分中发现的igf - 1含量明显较低。与饲喂酪蛋白饲料的大鼠相比，饲喂无蛋白饲料的大鼠肝脏中IGF-I-mRNA含量较低。这些结果清楚地显示了igf - 1在人类和其他动物的蛋白质或氨基酸营养中的重要作用。

Somatomedin C (or insulin-like growth factor-I, IGF-I) is a peptide hormone, the structure of which is known to be similar to insulin. However, IGF-I shows biological properties distinct from insulin. IGF-I has been elucidated to be produced mainly by liver under the control of growth hormone and nutritional status of animals. However, the effect of dietary proteins has not been studied extensively. This work was plained to elucidate the effect of dietary proteins on plasma immunoreactive (ir) IGF-I concentration, the mode of association of IGF-I with plasma IGF-binding proteins, and the correlation between plasma ir-IGF-I concentration and whole body protein synthesis rate.Nutritional quality of dietary proteins affected plasma ir-IGF-I extensively. The rats fed a casein diet showed the highest ir-IGF-I concentration and those given a protein- free diet, the lowest. Plasma ir-IGF-I of rats fed a gluten or corn gluten weal diet showed the intermediate values. Supplementation of lysine and threonine to the gluten diet or tryptophan and lysine to the corn gluten meal diet increased plasma ir-IGF-I concentration significantly.Nutritional value of dietary proteins also affected the mode of association of IGF-I with IGF-binding proteins. IGF-I in the plasma of rats fed casein diet was found primarily in the 150 kDa fraction. However, significantly lower amount of IGF-I was found in this fraction in the rats given the protein-free diet.The rats fed the protein-free diet contained lower amount of IGF-I-mRNA in liver compared with those fed the casein diet.These results clearly show the important role of IGF-I in protein or amino acid nutrition of man and other animals.