Maas J A, France J, Dijkstra J, Bannink A, McBride B W
Department of Animal and Poultry Science, University of Guelph, ON, Canada.
J Dairy Sci. 1998 Jun;81(6):1724-34. doi: 10.3168/jds.S0022-0302(98)75740-6.
A mathematical model is used to describe uptake by a countertransport system and subsequent flow of three amino acids (AA), Phe, Val, and Met, from arterial blood to milk protein in the mammary gland of a lactating cow. The model suggests that total uptake of all AA is higher than net uptake and that a large proportion of the incoming AA is released from the cell directly back to blood. The model is used to predict which of the three AA is limiting the rate of milk protein synthesis and the response to increased arterial concentration of the first-limiting AA. Simulations are performed to predict possible outcomes of several experimental protocols to AA infusion, which might be used to test in vivo the responsiveness of the bovine mammary gland to an altered arterial concentration of AA. Of the three AA considered, arterial Met concentration appears to be first-limiting. The infusion profile that gives the greatest response in milk protein synthesis rate alters the arterial profile of AA such that it is identical to that of proteins originating in the mammary gland. Model construction can be simplified by acknowledging normal biological constraints.
一个数学模型被用于描述反转运系统的摄取以及三种氨基酸（苯丙氨酸、缬氨酸和蛋氨酸）从动脉血到泌乳奶牛乳腺中乳蛋白的后续流动。该模型表明，所有氨基酸的总摄取量高于净摄取量，并且大部分进入的氨基酸直接从细胞释放回血液。该模型用于预测三种氨基酸中哪一种限制了乳蛋白合成速率以及对第一限制氨基酸动脉浓度增加的反应。进行模拟以预测几种氨基酸输注实验方案的可能结果，这些方案可用于体内测试牛乳腺对氨基酸动脉浓度改变的反应性。在所考虑的三种氨基酸中，动脉蛋氨酸浓度似乎是第一限制因素。在乳蛋白合成速率方面产生最大反应的输注模式会改变氨基酸的动脉分布，使其与源自乳腺的蛋白质的分布相同。通过承认正常的生物学限制，可以简化模型构建。
