Davis S R, Bickerstaffe R, Hart D S
Aust J Biol Sci. 1978 Apr;31(2):123-32. doi: 10.1071/bi9780123.
(1) The arterio-venous difference technique, previously used to measure mammary substrate uptake with cows and goats, was used to measure amino acid uptake by the mammary gland of the lactating Merino ewe. Possession of a single large superficial epigastric vein by the Merino ewe makes the Merino breed the most suitable for this type of study. (2) A method was developed enabling hourly measurement of milk yield without causing undue stress. Milk yield was essentially constant over a 7-8 h period. (3) Mammary extraction of most non-essential amino acids was low relative to output in milk protein and showed a greater variability with time than that found for the essential amino acids. There was a significant mammary extraction of ornithine and citrulline, neither amino acid being found in ovine milk protein. (4) Of the essential amino acids valine, isoleucine, leucine and arginine were taken up in excess of their requirement for milk protein synthesis. (5) On the basis of the extent of mammary extraction, methionine, lysine and leucine were first-, second- and third-limiting to the rate of milk protein synthesis. (6) Despite fluctuations in arterial amino acid concentrations the arterio-venous differences of the essential amino acids were relatively constant over a 7-8 h period. (7) The pattern of mammary amino acid uptake in the ewe is contrasted with that found in similar studies carried out with the lactating cow and goat.
(1) 以前用于测量奶牛和山羊乳腺底物摄取的动静脉差异技术，被用来测量泌乳美利奴母羊乳腺对氨基酸的摄取。美利奴母羊拥有一条单一的大的浅表腹壁静脉，这使得美利奴品种最适合这类研究。(2) 开发了一种方法，能够每小时测量产奶量而不会造成过度应激。在7 - 8小时的时间段内，产奶量基本恒定。(3) 相对于乳蛋白中的输出量，大多数非必需氨基酸的乳腺摄取量较低，并且与必需氨基酸相比，其随时间的变化更大。乳腺对鸟氨酸和瓜氨酸有显著摄取，而这两种氨基酸在绵羊乳蛋白中均未发现。(4) 在必需氨基酸中，缬氨酸、异亮氨酸、亮氨酸和精氨酸的摄取量超过了它们用于合成乳蛋白的需求量。(5) 根据乳腺摄取程度，蛋氨酸、赖氨酸和亮氨酸对乳蛋白合成速率分别为第一、第二和第三限制因素。(6) 尽管动脉氨基酸浓度有波动，但在7 - 8小时的时间段内，必需氨基酸的动静脉差异相对恒定。(7) 将母羊乳腺氨基酸摄取模式与对泌乳奶牛和山羊进行的类似研究所发现的模式进行了对比。
