Melatonin, considered as a main pineal product, may be also synthetized in the gastrointestinal tract from L-tryptophan. Melatonin has been recently shown to affect insulin release and its receptors have been characterized in the pancreas however, the effects of melatonin on the pancreatic enzyme secretion have not been examined. The aim of this study was to investigate the effects of melatonin or L-tryptophan on amylase secretion in vivo in anaesthetized rats with pancreato-biliary fistulas, and in vitro using isolated pancreatic acini. Melatonin (1, 5 or 25 mg/kg) or L-tryptophan (10, 50 or 250 mg/kg) given to the rats as a intraperitoneal (i.p.) bolus injection produced significant and dose-dependent increases in pancreatic amylase secretion under basal conditions or following stimulation of enzyme secretion by diversion of bile-pancreatic juice. This was accompanied by a dose-dependent rise in melatonin plasma level. Stimulation of pancreatic enzyme secretion caused by melatonin or L-tryptophan was completely abolished by vagotomy, deactivation of sensory nerves with capsaicin or pretreatment with CCK1 receptor antagonists (tarazepide or L-364,718). Pretreatment with luzindole, an antagonist of melatonin MT(2) receptor failed to affect melatonin- or L-tryptophan-induced amylase secretion. Administration of melatonin (1, 5 or 25 mg/kg i.p.) or L-tryptophan (10, 50 or 250 mg/kg i.p.) to the rats resulted in the dose-dependent increase of cholecystokinin (CCK) plasma immunoreactivity. Enzyme secretion from isolated pancreatic acini was not significantly affected by melatonin or L-tryptophan used at doses of 10(-8) -10(-5) M. We conclude that exogenous melatonin, as well as that produced endogenously from L-tryptophan, stimulates pancreatic enzyme secretion in vivo while increasing CCK release. Stimulatory effect of melatonin or L-tryptophan on the exocrine pancreas involves vagal sensory nerves and the CCK release by these substances.

中文翻译：

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褪黑素及其前体L-色氨酸：对体内和体外胰腺淀粉酶分泌的影响。

褪黑激素，被认为是松果树的主要产物，也可以由L-色氨酸在胃肠道中合成。最近已经证明褪黑激素会影响胰岛素的释放，并且已经在胰腺中表征了其受体，但是，尚未研究褪黑激素对胰腺酶分泌的影响。这项研究的目的是研究褪黑激素或L-色氨酸对麻醉的胰胆管瘘大鼠体内淀粉酶分泌的影响，以及在体外使用分离的胰腺腺泡蛋白的影响。以腹膜内（ip）的形式给予大鼠褪黑激素（1，5或25 mg / kg）或L-色氨酸（10，50或250 mg / kg）推注在基础条件下或通过转移胆胰液刺激酶分泌后，胰淀粉酶分泌显着且剂量依赖性增加。这伴随着褪黑激素血浆水平的剂量依赖性升高。通过褪黑激素切开术，用辣椒素使感觉神经失活或用CCK1受体拮抗剂（他拉西肽或L-364,718）预处理，完全可以消除由褪黑激素或L-色氨酸引起的胰腺酶分泌刺激。用luzindole预处理，褪黑激素MT（2）受体的拮抗剂未能影响褪黑激素或L-色氨酸诱导的淀粉酶的分泌。给大鼠施用褪黑激素（1、5或25 mg / kg ip）或L-色氨酸（10、50或250 mg / kg ip）导致胆囊收缩素（CCK）血浆免疫反应性呈剂量依赖性增加。从隔离的胰腺腺泡中分泌的酶不受褪黑素或L-色氨酸在10（-8）-10（-5）M剂量下的影响。我们得出结论，外源性褪黑素以及由L-色氨酸内生产生的褪黑素，在增加CCK释放的同时刺激体内胰腺酶的分泌。褪黑激素或L-色氨酸对外分泌胰腺的刺激作用涉及迷走感觉神经和这些物质释放的CCK。