Brammer G L
Neurobiochemistry Laboratory, West Los Angeles Veterans Affairs Medical Center, CA 90073.
Life Sci. 1994;55(10):775-87. doi: 10.1016/0024-3205(94)00561-3.
Markedly increased melatonin levels in plasma have been observed in response to tryptophan administration. This post-tryptophan melatonin increase has been attributed to the duodenum. Because extra-pineal sources of melatonin may be important in interpreting the meaning of altered melatonin production observed in patient populations, this work was undertaken to confirm whether melatonin is produced in the duodenum and to know whether the duodenum need be considered when investigating the circadian control of melatonin production. We measured melatonin in rat duodenum by HPLC both under basal conditions and following tryptophan load. No melatonin was observed in duodenum under conditions of 2.5 ng/g measurement limits. Neither was there any evidence found for the melatonin precursor N-acetylserotonin. Treatment with N-acetylserotonin resulted in increased melatonin content in the pineal gland, but no evidence for melatonin in the duodenum. In vitro incubation of duodenum tissue with 5-hydroxytryptophan, 5-methoxytryptophan, or N-acetylserotonin revealed no detectable melatonin synthesis, and incubation with melatonin revealed no detectable melatonin degradation. The lack of confirmation of melatonin content and the lack of either synthetic or degradative enzyme activity in duodenum tissue suggest that melatonin production from duodenum need not be considered in human or animal studies of melatonin production.
已观察到，给予色氨酸后血浆中褪黑素水平显著升高。色氨酸给药后褪黑素的增加归因于十二指肠。由于褪黑素的非松果体来源可能对解释在患者群体中观察到的褪黑素分泌变化的意义很重要，因此开展这项研究以确认十二指肠是否产生褪黑素，以及在研究褪黑素分泌的昼夜节律控制时是否需要考虑十二指肠。我们通过高效液相色谱法（HPLC）在基础条件下以及色氨酸负荷后测量大鼠十二指肠中的褪黑素。在测量限为2.5 ng/g的条件下，十二指肠中未观察到褪黑素。也没有发现褪黑素前体N-乙酰血清素的任何证据。用N-乙酰血清素处理导致松果体中褪黑素含量增加，但十二指肠中没有褪黑素的证据。用5-羟色氨酸、5-甲氧基色氨酸或N-乙酰血清素对十二指肠组织进行体外孵育，未检测到褪黑素合成，用褪黑素孵育也未检测到褪黑素降解。十二指肠组织中缺乏褪黑素含量的证实以及合成或降解酶活性，这表明在人类或动物褪黑素分泌研究中无需考虑十二指肠产生褪黑素的情况。
