Effect of high protein diets and rumen by-pass amino acids on bone growth in sheep

本研究旨在阐明高蛋白饲粮和直接到达肠道上部的氨基酸对钙代谢和骨生长代谢的影响。高蛋白饲粮提高了绵羊的表观钙吸收和钙潴留。高蛋白饮食也增加了尿钙排泄。尿钙排泄量的增加被认为是由肾脏钙滤过率的增加和肾小管钙重吸收的微小变化引起的。血浆钙浓度有轻微降低的趋势，血浆羟脯氨酸浓度（骨吸收的标志）显著升高。血浆甲状旁腺激素浓度也因饲喂高蛋白饲料而升高。因此，可以得出结论，高蛋白饮食可能激活钙和骨代谢。在EDTA输注试验中，饲喂高蛋白日粮的羊的钙动员量大于饲喂对照日粮的羊。本实验结果支持高蛋白饮食能促进骨代谢的结论。皱胃内灌注酪蛋白有增加血浆生长抑素C浓度和明显增加血浆胰岛素浓度的趋势。另一方面，血浆骨钙素浓度是骨形成的一个指标，酪蛋白输注没有改变。这些结果表明，优质蛋白流入小肠可能促进骨生长，而酪蛋白输注的反应可能受动物生长阶段的影响。胃内灌注丙氨酸和天冬酰胺酸增加血浆胰岛素浓度，同时降低血浆生长激素C浓度。氨基酸的种类和吸收量改变了与骨代谢和生长有关的激素反应，这一点值得注意。

The study was conducted to elucidate the effect of high protein diets and amino acids reached directly at the upper part of intestine on calcium metabolism, and bone growth and metabolism. Apparent calcium absorption and calcium retention were increased in sheep fed high protein diets. Urinary calcium excretion was also increased by feeding high protein diets. The increase in urinary calcium excretion was thought to be induced by an increase in renal filtration rate of calcium and by little change in calcium reabsorption of renal tubule.Plasma calcium concentration tended to be slightly reduced, and plasma hydroxyproline concentration, which is a marker of bone resorption, was significantly increased in sheep fed the high protein diets. Plasma parathyroid hormone concentration was also elevated by feeding the high protein diets. Therefore, it may be concluded that high protein diets are likely to activate calcium and bone metabolism.In experiments of EDTA infusion, calcium mobilization was larger in sheep fed a high protein diet than in sheep fed a control diet. The results from this experiment support the conclusion that a high protein diet activates bone metabolism.The intra-abomasal infusion of casein tended to increase plasma somatomedin C concentrations and obviously increased plasma insulin concentrations. On the other hand, plasma osteocalcin concentrations which is an indicator of bone formation was not changed by casein infusion. These results indicate that the inflow of high quality protein into the small intestine is likely to enhance bone growth while the response for casein infusion may be affected by the growth stage of animals. The intra-abomasal infusion of alanine and asparaginic acid increased plasma insulin concentrations, while reduced plasma somatomedin C concentrations. It was considerable that hormonal response connected with bone metabolism and growth is changed by a kind and an amount of absorbed amino acid.