Lactogenic actions of amino acids by activating endocrine systems in the ruminant.

生长激素(GH)、胰岛素和胰高血糖素是控制能量分配的主要激素，有助于提高反刍动物的产奶量。我们之前曾报道，绵羊体内这些激素的分泌被几种氨基酸修饰(Kuhara等人，1991)。本研究旨在探讨饲喂氨基酸对哺乳期山羊激素和代谢产物浓度的影响。试验一，提高日粮中氨基酸的比例，以适应维持哺乳所需的能量需求。在试验2中，为了满足能量需求，增加了日粮比例。在这两个实验中，将两种氨基酸(天冬氨酸、亮氨酸、丙氨酸和甘氨酸)中的任何一种以3 mmol/kg体重/30min的速度注入哺乳期和非哺乳期动物的颈静脉。试验3以试验1的能量水平连续给药6天。试验1在哺乳期补充氨基酸，促进生长激素的分泌，抑制胰岛素的分泌。在哺乳期给药抑制了氨基氮浓度的升高，但增加了游离脂肪酸浓度的升高。产奶量与血浆IGF-I浓度呈显著正相关。但在实验2中，生长激素反应受到抑制，基础胰岛素和胰升糖素浓度在哺乳期升高。在试验3中，持续输注氨基酸使生长激素、胰岛素和胰高血糖素浓度升高，但在哺乳期和非哺乳期之间变化不显著。这些结果表明，哺乳期山羊在维持能量水平上表现为用力反应(分解代谢)，而在过剩能量水平上表现为合成反应(合成代谢)。然而，提高产奶量的方法还有待进一步研究。

It is established that growth hormone (GH), insulin and glucagon are major hormones to control energy distribution, contributing to increase milk yield in the ruminants. We previously reported that the secretion of these hormones was modified by several amino acids in sheep (Kuhara et al., 1991). The aim of the present study was to investigate the effects of administration of amino acids on hormone and metabolite concentrations in lactating goats.In Experiment 1, the ration was increased to fit the energy requirement for maintenance of lactation. In Experiment 2, the ration was increased to overcome the energy requirement. In both Experiments, either of amino acids (Asp, Leu, Ala and Gly) was infused into the jugular vein of lactating and non-lactating animals at 3 mmol/kg B.W./30 min. In Experiment 3, the administration was continued for 6 days at the energy level of Experiment 1.In Experiment 1, secretory increment of GH in response to the amino acid administration was enhanced, while that of insulin was suppressed during the lactating period. A rise in amino N concentration was suppressed, but that in FFA concentration was enhanced, in response to the administration during the lactating period. A significantly positive interaction was observed between milk yield and plasma IGF-I concentration. In Experiment 2, however, GH response was suppressed, and the basal concentration of insulin and glucagon was increased during the lactating period. In Experiment 3, the concentration of GH, insulin and glucagon was raised by the continuous infusion of amino acid, but the significant change was not found between lactaing and non-lactating periods. From these results, we conclude that lactating goats showed exergonic reactions (catabolism) at the maintenance energy level, whereas they did synthetic reactions (anabolism) at the excess energy level. However, further study on the method to increase milk yield remains to be investigated.