Mitch W E, Walser M, Sapir D G
J Clin Invest. 1981 Feb;67(2):553-62. doi: 10.1172/JCI110066.
We measured the effects of seven consecutive daily infusions of alpha-ketoisocaproate (the alpha-keto analogue of leucine) or leucine itself on urinary urea and total nitrogen excretion during fasting. Two study protocols were undertaken. In protocol I, subjects underwent three separate 14-d fasts: one during which 34 mmol/d of leucine were infused on days 1--7; a second during which 34 mmol/d of alpha-ketoisocaproate were infused on days 1--7; and a third control fast during which no infusions were given. Infusions of alpha-ketoisocaproate significantly reduced daily urine urea nitrogen excretion compared with both the control fasts and the fasts in which leucine was infused (P less than 0.001). This nitrogen-sparing effect of alpha-ketoisocaproate persisted during days 8--14 even though no further infusions were given. Daily urinary urea nitrogen excretion during fasts when leucine was administered did not differ from values observed during control fasts. In protocol II, subjects were starved on two occasions for 14 d. During one fast, infusions of 11 mmol/d of alpha-ketoisocaproate were given on days 1--7; during the control fast, no infusions were given. Daily urine urea nitrogen excretion was lower (P less than 0.001) on days 1--7 and also on days 8--14 of the fast during which alpha-ketoisocaproate was given. The nitrogen-sparing effect of alpha-ketoisocaproate could not be related to changes in circulating levels of amino acids, ketone bodies, or insulin in either protocol. We conclude that alpha-ketoisocaproate infusions decrease the nitrogen wasting of starvation, whereas leucine, studied under identical conditions, does not.
我们测定了连续7天每日输注α-酮异己酸（亮氨酸的α-酮类似物）或亮氨酸本身对禁食期间尿尿素和总氮排泄的影响。进行了两项研究方案。在方案I中，受试者进行了3次单独的14天禁食：一次在第1 - 7天输注34 mmol/d的亮氨酸；第二次在第1 - 7天输注34 mmol/d的α-酮异己酸；第三次为对照禁食，期间不进行输注。与对照禁食和输注亮氨酸的禁食相比，输注α-酮异己酸显著降低了每日尿尿素氮排泄（P < 0.001）。即使在第8 - 14天不再进行输注，α-酮异己酸的这种氮节约效应仍然持续。给予亮氨酸时禁食期间的每日尿尿素氮排泄与对照禁食期间观察到的值没有差异。在方案II中，受试者两次饥饿14天。在一次禁食期间，第1 - 7天给予11 mmol/d的α-酮异己酸输注；在对照禁食期间，不进行输注。在给予α-酮异己酸的禁食的第1 - 7天以及第8 - 14天，每日尿尿素氮排泄均较低（P < 0.001）。在任何一个方案中，α-酮异己酸的氮节约效应都与循环中氨基酸、酮体或胰岛素水平的变化无关。我们得出结论，输注α-酮异己酸可减少饥饿时的氮消耗，而在相同条件下研究的亮氨酸则没有这种作用。
