Boling J A, Katanyukul P J, Nuzum C T
Int J Vitam Nutr Res. 1976;46(3):395-9.
Eleven Southdown male lambs averaging 19.8 kg were randomly allotted to two groups and fed diets containing 7.7% (low-N) or 15.8% (high-N) crude protein. All of the supplemental nitrogen in the high-N diet was supplied as urea. Intake of the low-N and high-N diets averaged 372.3 g and 340.5 g/day, respectively. Findings at the end of the thirty-day trial were: (1) mean body weights unchanged for the two groups; (2) plasma urea nitrogen three-fold higher in the high-N (19.07 mg/100 ml) than the low-N (6.57) animals; (3) similar hepatic activity levels of three urea cycle enzymes (ornithine transcarbamylase, argininosuccinase, arginase) in the two groups, and (4) similar liver weights and liver protein concentration. The absence of adaptive change in enzyme levels suggests the hypothesis that addition of non-protein nitrogen to maintenance diets may cause ammonia intoxication by exceeding the liver's reserve capacity for urea synthesis.
11只平均体重为19.8千克的萨福克雄性羔羊被随机分为两组，分别饲喂粗蛋白含量为7.7%（低氮）或15.8%（高氮）的日粮。高氮日粮中的所有补充氮均以尿素形式提供。低氮和高氮日粮的摄入量分别平均为372.3克/天和340.5克/天。三十天试验结束时的结果如下：（1）两组的平均体重均未改变；（2）高氮组动物（19.07毫克/100毫升）的血浆尿素氮比低氮组动物（6.57毫克/100毫升）高三倍；（3）两组三种尿素循环酶（鸟氨酸转氨甲酰酶、精氨琥珀酸酶、精氨酸酶）的肝脏活性水平相似；（4）肝脏重量和肝脏蛋白质浓度相似。酶水平未出现适应性变化，这表明在维持日粮中添加非蛋白氮可能会因超过肝脏合成尿素的储备能力而导致氨中毒的假设。
