Regulation of secretion of growth hormone, somatomedin-C and pancreatic hormones by amino acids in ruminants.

近年来，外源性生长激素对奶牛产奶量的影响受到了广泛的关注。生长激素的作用可能包括刺激吸收的营养物质的分解代谢，为乳腺提供能量的底物和可用于产生乳成分的底物。当体内的能量分配指向分解代谢时。人们可能期望通过增加对乳腺的底物供应来提高产奶量。相比之下。合成代谢能量分配似乎是刺激牛肉生产的理想选择。反刍动物和其他物种一样，分解代谢或合成代谢的能量分配方向主要由生长激素、生长激素c （Sm-C）、胰岛素和胰高血糖素等代谢激素调节。已知有几种氨基酸会影响代谢激素的分泌。由于这些激素也是调节氨基酸代谢的核心，因此有必要对每种氨基酸刺激这些激素分泌的程度进行量化。亮氨酸是刺激胰岛素分泌最有效的氨基酸，但不会增加胰高血糖素和生长激素的分泌。丙氨酸、甘氨酸和丝氨酸比其他氨基酸更能促进胰高血糖素和胰岛素的分泌。没有一种氨基酸能够在不增加胰岛素或生长激素分泌的情况下特异性刺激胰高血糖素分泌。至于胰岛素和胰高血糖素的分泌，氨基酸可以根据其r结构进行分组。中性直链氨基酸刺激胰岛素和胰高血糖素的分泌，对较短的c链氨基酸的分泌反应更大。支链氨基酸倾向于提高胰岛素和抑制胰高血糖素的分泌。酸性氨基酸导致生长激素分泌增加。天冬氨酸对生长激素的刺激作用最强，超过精氨酸。长时间十二指肠内给予亮氨酸可增强Sm-C分泌。少

Much attention has recently been Paid to the effects of the exogenous administration of GH in increasing milk production of dairy cows. The effect of GH could involve the stimulation of catabolism of absorbed nutrients providing energy-yielding substrates for the maffimary gland and substrates that can be utilized to produce milk constituents. When energy partition in the body is directed towards catabolism. one may expect an enhanced milk production via increased substrate supply to the mammary gland. By contrast. an anabolic energy partition appears to be desirable to stimulate beef production. In ruminant animals, as in the other species, the direction of energy partition toward catabolism or anabolism is mostly regulated by metabolic hormones such as GH, somatomedin-C (Sm-C), insulin and glucagon.Several amino acids are known to affect the secretion of metabolic hormones. As these hormones are also central to the regulation of amino acid metabolism, it is worthwhile to quantify the … More extent to which each amino acid can stimulate the secretion of these hormones.Leucine was the most effective amino acid in stimulating insulin secretion but did not produce any increase in glucagon and GH secretion. Alanine, glycine and serine induced a greater enhancement of both glucagon and insulin secretion than other amino acids. No amino acid was able to specifically stimulate glucagon secretion without also increasing insulin or GH secretion. As regards insulin and glucagon secretion, amino acids could be divided into groups according to their R-structures. Neutral straight chain amino acids stimulated both insulin and glucagon secretion, with a greater secretory response to shorter C-chain amino acids. Branched chain amino acids tended to enhance insulin and suppress glucagon secretion. Acidic amino acids caused an increase in GH secretion. Aspartic acid caused the strongest stimulation of GH secretion, exceeding that induced by arginine. Prolonged intraduodenal administration of leucine enhanced Sm-C secretion. Less