Havassy I, Bŏda K, Kosta K, Rybosová E
Physiol Bohemoslov. 1976;25(4):333-40.
Two sheep with a low and high nitrogen intake (7.6 and 24 g N/day respectively) were given a single intravenous dose of 15N-labelled urea (15.3 mg 15N/kg b.w.) The findings were as follows. The greater part of non-retained 15N from the administered dose was excreted during the first day after the intravenous administration of 15N-urea. Daily excretion in the faeces amounted to 1.35-2.37% of the 15N in the given dose. With a low N intake, more 15N from the given dose (59.4%) was retained in the N pool than with a high N intake (50.5%). The net passage of 15N into the rumen and 15N incorporation into the amide-N of the plasma proteins was likewise greater. 15N incorporation into the amide-N of the plasma proteins rose steadily for 3 days. The porportion of amidic 15N in the plasma proteins rose steadily for 3 days. The proportion of amidic 15N in the plasma protein total 15N changed on the second and third day after administering 15N-urea from 8% to 16%, with the maximum at the beginning of the second day. The amount of 15N incorporated into the proteins in 1 litre plasma attained up to 3% of the given dose. It is concluded from the results that the synthesis of amino acids and their amide groups is both a quantitatively and a qualitatively important metabolic route for the reutilization of blood urea nitrogen for protein synthesis in ruminants.
给两只氮摄入量分别为低量和高量（分别为7.6克氮/天和24克氮/天）的绵羊静脉注射单次剂量的15N标记尿素（15.3毫克15N/千克体重）。结果如下。给药剂量中未被保留的15N大部分在静脉注射15N尿素后的第一天排出。粪便中的日排泄量相当于给定剂量中15N的1.35 - 2.37%。与高氮摄入量（50.5%）相比，低氮摄入量时给定剂量中更多的15N（59.4%）保留在氮池中。15N进入瘤胃的净通量以及15N掺入血浆蛋白酰胺氮中的量同样更大。15N掺入血浆蛋白酰胺氮中的量持续3天稳步上升。血浆蛋白中酰胺态15N的比例持续3天稳步上升。在注射15N尿素后的第二天和第三天，血浆蛋白中酰胺态15N占总15N的比例从8%变为16%，在第二天开始时达到最高。每升血浆中掺入蛋白质的15N量高达给定剂量的3%。从结果得出结论，氨基酸及其酰胺基团的合成对于反刍动物将血液尿素氮再利用于蛋白质合成而言，在数量和质量上都是重要的代谢途径。
