Rebouche C J, Chenard C A
Department of Pediatrics, University of Iowa College of Medicine, Iowa City, IA 52242.
J Nutr. 1991 Apr;121(4):539-46. doi: 10.1093/jn/121.4.539.
Results of kinetic and pharmacokinetic studies have suggested that dietary carnitine is not totally absorbed and is in part degraded in the gastrointestinal tract of humans. To determine the metabolic fate of dietary carnitine in humans, we administered orally a tracer dose of [methyl-3H]L-carnitine with a meal to subjects who had been adapted to a low-carnitine diet or a high-carnitine diet. Urinary and fecal excretion of radiolabeled carnitine and metabolites was monitored for 5 to 11 d following administration of the test dose. Total radioactive metabolites excreted ranged from 13 to 34% (low carnitine diet) and 27 to 46% (high carnitine diet) of the ingested tracer. Major metabolites found were [3H]trimethylamine N-oxide (8 to 39% of the administered dose; excreted primarily in urine) and [3H]gamma-butyrobetaine (0.09 to 8% of the administered dose; excreted primarily in feces). Urinary excretion of total carnitine was 42 to 95% (high carnitine diet) and 190 to 364% (low carnitine diet) of intake. These results indicate that oral carnitine is 54 to 87% bioavailable from normal Western diets; the percentage of intake absorbed is related to the quantity ingested.
动力学和药代动力学研究结果表明，膳食中的肉碱并非完全被吸收，部分会在人体胃肠道中降解。为了确定膳食肉碱在人体内的代谢归宿，我们让适应低肉碱饮食或高肉碱饮食的受试者随餐口服示踪剂量的[甲基 - ³H]L - 肉碱。在给予测试剂量后，对放射性标记的肉碱及其代谢产物的尿液和粪便排泄情况进行了5至11天的监测。排出的总放射性代谢产物占摄入示踪剂的13%至34%（低肉碱饮食）和27%至46%（高肉碱饮食）。发现的主要代谢产物是[³H]三甲胺N - 氧化物（占给药剂量的8%至39%；主要经尿液排出）和[³H]γ - 丁酸甜菜碱（占给药剂量的0.09%至8%；主要经粪便排出）。总肉碱的尿液排泄量为摄入量的42%至95%（高肉碱饮食）和190%至364%（低肉碱饮食）。这些结果表明，正常西方饮食中口服肉碱的生物利用度为54%至87%；吸收的摄入量百分比与摄入的量有关。
