Morrison D J, Dodson B, Preston T, Weaver L T
Department of Child Health, University of Glasgow, Yorkhill Hospitals, Glasgow, G3 8SJ UK.
Eur J Clin Nutr. 2003 Aug;57(8):1017-24. doi: 10.1038/sj.ejcn.1601637.
Lactose [(13)C]ureide has been proposed as a noninvasive marker for oro-caecal transit time in adults and children. The present study investigates the handling of lactose [(13)C]ureide ((13)C LU) and glucose [(13)C]ureide ((13)C GU) by the gastrointestinal tract and describes the metabolic fates of these substrates and describes the extent of tracer excretion by different routes.
Four subjects underwent five studies in which they ingested a test meal plus (1) no substrate, (2) (13)C LU, (3) (13)C GU, (4) (13)C LU after predosing with unlabelled lactose ureide and (5) (13)C LU after predosing with glucose ureide. Subjects were studied at home with at least 1 week between tests and they all completed the study. Breath was analysed for (13)CO(2) recovery and urine was analysed for total (13)C recovery, (13)C urea recovery and (13)C GU recovery.
The profiles and extent of tracer recovery in breath and urine were similar when either (13)C GU or (13)C LU was used, suggesting similar handling of these substrates by the gut. (13)C GU was the major (13)C-enriched species recovered in the urine even when (13)C LU was consumed. Predosing with either lactose ureide or glucose ureide increased the rate of appearance of tracer, but did not alter transit times.
(13)C LU is hydrolysed to (13)C GU in the small intestine with the fraction of (13)C GU appearing in the urine probably limited by small intestinal permeability. Either (13)C LU or (13)C GU can be used to measure oro-caecal transit time.
乳糖[（13）C]脲已被提议作为成人和儿童口盲肠转运时间的非侵入性标志物。本研究调查了胃肠道对乳糖[（13）C]脲（（13）C LU）和葡萄糖[（13）C]脲（（13）C GU）的处理情况，描述了这些底物的代谢命运，并描述了示踪剂通过不同途径排泄的程度。
四名受试者进行了五项研究，他们摄入一顿试验餐加（1）无底物，（2）（13）C LU，（3）（13）C GU，（4）在预先服用未标记的乳糖脲后服用（13）C LU，以及（5）在预先服用葡萄糖脲后服用（13）C LU。受试者在家中进行研究，两次测试之间至少间隔1周，他们均完成了研究。分析呼出气体中的（13）CO2回收率，并分析尿液中的总（13）C回收率、（13）C尿素回收率和（13）C GU回收率。
使用（13）C GU或（13）C LU时，呼出气体和尿液中示踪剂回收的曲线和程度相似，表明肠道对这些底物的处理方式相似。即使摄入（13）C LU，（13）C GU仍是尿液中回收的主要富含（13）C的物质。预先服用乳糖脲或葡萄糖脲会增加示踪剂的出现速率，但不会改变转运时间。
（13）C LU在小肠中水解为（13）C GU，出现在尿液中的（13）C GU部分可能受小肠通透性限制。（13）C LU或（1）C GU均可用于测量口盲肠转运时间。
