This study determined whether extracellular citrulline is degraded by ruminal bacteria of sheep. In the first experiment, whole rumen fluid (3 mL) from six adult Suffolk sheep was incubated at 37 °C with 5 mM l-glutamine (Gln), l-glutamate (Glu), l-arginine (Arg), or l-citrulline (Cit) for 0, 0.5, 1, and 2 h or with 0, 0.5, 2, or 5 mM Gln, Glu, Arg, or Cit for 2 h. An aliquot (50 µL) of the incubation solution was collected at the predetermined time points for amino acids (AA) analyses. Results showed extensive hydrolysis of Gln into Glu and ammonia, of Arg into l-ornithine and l-proline, but little or no degradation of extracellular Cit or Glu by ruminal microbes. In the second experiment, six adult Suffolk sheep were individually fed each of three separate supplements (8 g Gln , Cit, or urea) on three separate days along with regular feed (800 g/animal). Blood (2 mL) was sampled from the jugular vein prior to feeding (time 0) and at 0.5, 1, 2, and 4 h after consuming the supplement. Plasma was analyzed for AA, glucose, ammonia, and urea. The concentrations of Cit in the plasma of sheep consuming this AA increased (P < 0.001) by 117% at 4 h and those of Arg increased by 23% at 4 h, compared with the baseline values. Urea or Gln feeding did not affect (P > 0.05) the concentrations of Cit or Arg in plasma. These results indicate that Cit is not metabolized by ruminal microbes of sheep and is, therefore, absorbed as such by the small intestine and used for the synthesis of Arg by extrahepatic tissues.

中文翻译：

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成年羊的瘤胃微生物不会降解细胞外的 L-瓜氨酸。


本研究确定了细胞外瓜氨酸是否被绵羊瘤胃细菌降解。在第一个实验中，将来自六只成年萨福克羊的全瘤胃液 (3 mL) 在 37 °C 下与 5 mM l-谷氨酰胺 ( Gln )、 l-谷氨酸 ( Glu )、 l-精氨酸 ( Arg ) 或l-瓜氨酸 ( Cit ) 0、0.5、1 和 2 小时，或使用 0、0.5、2 或 5 mM Gln、Glu、Arg 或 Cit 2 小时。在预定时间点收集等份 (50 µL) 孵育溶液，用于氨基酸 ( AA ) 分析。结果表明，Gln 广泛水解为 Glu 和氨，Arg 广泛水解为L-鸟氨酸和L-脯氨酸，但瘤胃微生物很少或没有降解细胞外 Cit 或 Glu。在第二个实验中，六只成年萨福克羊在三天内分别饲喂三种不同的补充剂（8 g Gln、Cit 或尿素）以及常规饲料（800 g/动物）。在喂食前（时间 0）以及食用补充剂后 0.5、1、2 和 4 小时从颈静脉采集血液 (2 mL)。分析血浆中的 AA、葡萄糖、氨和尿素。与基线值相比，食用该 AA 的绵羊血浆中 Cit 浓度在 4 小时时增加了 117%（ P < 0.001），Arg 浓度在 4 小时时增加了 23%。尿素或谷氨酰胺喂养不影响（ P >0.05）血浆中Cit或Arg的浓度。这些结果表明，Cit 不被绵羊的瘤胃微生物代谢，因此被小肠吸收并被肝外组织用于合成 Arg。