Mutsvangwa T, Buchanan-Smith J G, McBride B W
Department of Animal and Poultry Science, University of Guelph, Ontario, Canada.
J Nutr. 1996 Jan;126(1):209-18. doi: 10.1093/jn/126.1.209.
The effects of ammonia (as NH4Cl) and propionate on the partitioning of amino acids between oxidation and gluconeogenesis were determined in isolated hepatocytes obtained from sheep fed a basal diet (50:50 bromegrass hay:corn; asfed basis) with or without urea. Hepatocyte suspensions were incubated with NH4Cl (0, 1.25, 2.5 and 5.0 mmol/L) and/or propionate (0, 2.5 and 5.0 mmol/L), in the presence of either 2.5 mmol/L L-alanine and 18.5 kBq L-[1-14C]alanine or 2.5 mmol/L L-glutamate and 18.5 kBq L-[1-14C]glutamate. Increasing the level of ruminal degradable nitrogen with urea increased in vitro rates of oxidation to 14CO2 of [1-14C]alanine, but not [1-14C]glutamate. Increasing in vitro concentrations of NH4Cl and propionate between 0 and 5 mmol/L reduced the rates of oxidation to 14CO2 of both [1-14C]alanine and [1-14C]glutamate. Synthesis of [14C]glucose with [1-14C]alanine, but not [1-14C]glutamate as the substrate, was increased 100% by feeding urea. Increasing in vitro levels of NH4Cl between 0 and 5 mmol/L reduced the rates of conversion of [1-14C]alanine and [1-14C]glutamate to [14C]glucose in hepatocytes isolated from sheep fed both diets. Increasing in vitro levels of propionate between 0 and 2.5 mmol/L elevated production rates of [14C]glucose from both radiotracers, but from 2.5 to 5.0 mmol/L propionate no further increase was evident. Feeding urea increased in vitro rates of urea nitrogen production. Increasing propionate levels between 0 and 5 mmol/L reduced ureagenic rates in liver cells isolated from sheep fed both diets. Oxygen (O2) uptake was unaffected by diet and NH4Cl; however, increasing propionate between 0 and 5 mmol/L increased rates of O2 uptake. It is concluded that in isolated sheep hepatocytes, detoxification of excessive ammonia may cause a repartitioning of alanine and glutamate metabolism towards oxidation and gluconeogenesis.
在从饲喂基础日粮（50:50 雀麦草干草:玉米；按风干基础）且添加或不添加尿素的绵羊获取的离体肝细胞中，测定了氨（以氯化铵形式）和丙酸盐对氨基酸在氧化和糖异生之间分配的影响。肝细胞悬液在存在 2.5 mmol/L L-丙氨酸和 18.5 kBq L-[1-14C]丙氨酸或 2.5 mmol/L L-谷氨酸和 18.5 kBq L-[1-14C]谷氨酸的情况下，与氯化铵（0、1.25、2.5 和 5.0 mmol/L）和/或丙酸盐（0、2.5 和 5.0 mmol/L）一起孵育。用尿素提高瘤胃可降解氮水平会增加[1-14C]丙氨酸氧化为 14CO2 的体外速率，但不会增加[1-14C]谷氨酸的氧化速率。将体外氯化铵和丙酸盐浓度在 0 至 5 mmol/L 之间增加会降低[1-14C]丙氨酸和[1-14C]谷氨酸氧化为 14CO2 的速率。以[1-14C]丙氨酸而非[1-14C]谷氨酸为底物合成[14C]葡萄糖，通过饲喂尿素增加了 100%。将体外氯化铵水平在 0 至 5 mmol/L 之间增加会降低从两种日粮饲喂的绵羊分离的肝细胞中[1-14C]丙氨酸和[1-14C]谷氨酸转化为[14C]葡萄糖的速率。将体外丙酸盐水平在 0 至 2.5 mmol/L 之间增加会提高两种放射性示踪剂生成[14C]葡萄糖的速率，但从 2.5 至 5.0 mmol/L 丙酸盐时，未观察到进一步增加。饲喂尿素会增加体外尿素氮生成速率。将丙酸盐水平在 0 至 5 mmol/L 之间增加会降低从两种日粮饲喂的绵羊分离的肝细胞中的尿素生成速率。氧气（O2）摄取不受日粮和氯化铵影响；然而，将丙酸盐在 0 至 5 mmol/L 之间增加会提高 O2 摄取速率。得出的结论是，在离体绵羊肝细胞中，过量氨的解毒可能导致丙氨酸和谷氨酸代谢重新分配至氧化和糖异生方向。
