胰腺自分泌多巴胺经D1受体调节胰岛素分泌的机制研究

Dopamine (DA) synthesized in pancreas can regulate insulin secretion and blood glucose level. But which part of pancreas the DA comes from, exocrine or endocrine, and how it regulates insulin secretion remains unclear. It has been reported that the rate-limiting enzyme for DA synthesis is distributed in the pancreatic acinar, while the DA transporter is located in the islet β cells. We have detected a high concentration of levodopa (L-DOPA) in pancreatic juice and wide distribution of DA receptors in pancreatic islets, among which the D1 receptors are only localized in β cells. We hypothesize that acinar cells may uptake tyrosine for L-DOPA synthesis; islets cells synthesize DA by taking the L-DOPA from acinar cells, not tyrosine; and by binding with D1 receptors on the islet β cells the DA stimulates insulin secretion in an autocrine manner. The present study aims to investigate the structural communication between endocrine and exocrine pancreas; the synthesis of DA in islets, the manner of DA released by islet β cell, and the signaling pathway underlying the DA modulating insulin secretion by means of immunofluorescence, selective destruction of pancreatic β cells, acinar/islet cell culture and co-culture, flow cytometry, RNA interference/gene knockdown and radioactive detection etc. The present study may reveal the synthesis and autocrine of DA in pancreas and the mechanisms underlying the regulation of pancreatic DA on insulin secretion. In addition, it might also provide some theoretical and experimental evidence for searching drug target of diabetes' diagnosis and treatment.

胰腺可以合成多巴胺（DA），而DA可以调节血糖和胰岛素分泌，但DA来自胰腺外分泌部还是内分泌部、它如何调节胰岛素分泌均不清楚。有报道合成DA的限速酶分布在胰腺腺泡、而DA转运体在胰岛β细胞。我们发现胰液中存在高浓度左旋多巴（L-DOPA），DA受体大量分布在胰岛，其中D1受体定位在β细胞。我们推测腺泡细胞利用酪氨酸合成L-DOPA；L-DOPA经胰腺导管到达胰岛β细胞合成DA；DA通过自分泌作用于D1受体调节胰岛素分泌。本项目将采用免疫荧光、选择性胰岛β细胞破坏、腺泡/胰岛细胞培养与共培养、流式细胞、RNA干扰/基因敲除等深入研究胰腺内/外分泌之间联系的形态结构；胰液中L-DOPA的来源；明确胰岛合成DA的前体；以及胰岛β细胞自分泌DA通过D1受体调节胰岛素分泌。本研究有助于揭示胰腺DA的合成过程及其通过D1调节胰岛素分泌的机制，有望为探索糖尿病诊治的药物靶点提供可靠的理论与实验依据。

胰腺自身可以合成多巴胺（dopamine, DA），并且DA可以调节胰岛素的释放，DA受体广泛分布于胰腺组织中，其中D1受体主要分布在胰岛β细胞上。但胰腺DA合成的具体过程、其作用于胰岛β细胞的D1受体对胰岛素分泌的影响等并不清楚。本研究采用HPLC测定DA含量，发现胰液中含有高浓度的左旋多巴（L-DOPA）和DA；应用免疫荧光结合激光共聚焦扫描技术观察发现酪氨酸羟化酶（TH）和芳香族氨基酸脱羧酶（AADC）分别位于胰腺的内外分泌部，多巴胺转运体（DAT）位于β细胞上，D1受体也表达在β细胞上。进一步通过在体糖耐量试验、胰液引流和离体孵育胰腺组织、原代分离的大鼠胰岛、大鼠腺泡细胞系（AR42J细胞）和胰岛β细胞系（INS-1细胞）等方法，发现腺泡细胞可以利用酪氨酸合成L-DOPA，胰岛β细胞可以利用L-DOPA合成DA；DA可以促进葡萄糖刺激引起的胰岛素分泌，而且可以被D1受体拮抗剂SCH23390所阻断；D1受体激动剂SKF38393可以降低血糖，促进胰岛素的分泌，并被SCH23390所阻断。本研究发现胰源性DA需要内外分泌部的共同协作来完成，DA可以通过作用于β细胞上的D1受体促进胰岛素的分泌，改善糖耐量情况，为DA相关药物在治疗糖尿病方面提供理论与实验依据。