Recent investigations of our group established that melatonin modulates hormone secretion of pancreatic islets via melatonin receptor types MT1 and MT2. Expression of MT1 and MT2 has been shown in mouse, rat, and human pancreatic islets as well as in the β‐, α‐, and δ‐cell lines INS‐1, αTC1.9, and QGP‐1. In view of these earlier investigations, this study was performed to analyze in detail the distribution and density of melatonin receptors on the main islet cell types in human pancreatic tissue obtained from nondiabetic and type 2 diabetic patients. Immunohistochemical analysis established the presence of MT1 and MT2 in β‐, α‐, and δ‐cells, but notably, with differences in receptor density. In general, the lowest MT1 and MT2 receptor density was measured in α‐cells compared to the 2 other cell types. In type 2 diabetic islets, MT1 and MT2 receptor density was increased in δ‐cells compared to normoglycemic controls. In human islets in batch culture of a nondiabetic donor, an increase of somatostatin secretion was observed under melatonin treatment while in islets of a type 2 diabetic donor, an inhibitory influence could be observed, especially in the presence of 5.5 mmol/L glucose. These data suggest the following: i) cell‐type‐specific density of MT1 and MT2 receptors in human pancreatic islets, which should be considered in context of the hormone secretion of islets, ii) the influence of diabetes on density of MT1 and MT2 as well as iii) the differential impact of melatonin on somatostatin secretion of nondiabetic and type 2 diabetic islets.

中文翻译：

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褪黑素受体在人类主要胰岛细胞类型中的分布和密度

我们小组的最新研究表明，褪黑激素通过以下途径调节胰岛的激素分泌：褪黑激素受体类型MT1和MT2。MT1和MT2的表达已在小鼠，大鼠和人类胰岛以及β-，α-和δ-细胞系INS-1，αTC1.9和QGP-1中显示。鉴于这些早期研究，进行了这项研究以详细分析从非糖尿病和2型糖尿病患者获得的人胰腺组织中主要胰岛细胞类型上褪黑激素受体的分布和密度。免疫组织化学分析确定了MT细胞和MT2在β细胞，α细胞和δ细胞中的存在，但值得注意的是，受体密度存在差异。通常，与其他2种细胞类型相比，在α细胞中测得的MT1和MT2受体密度最低。与正常血糖对照组相比，在2型糖尿病胰岛中，δ细胞的MT1和MT2受体密度增加。在非糖尿病供体的分批培养中的人胰岛中，褪黑激素治疗后生长抑素分泌增加，而在2型糖尿病供体的胰岛中，尤其是在5.5 mmol / L葡萄糖存在下，可观察到抑制作用。这些数据表明：i）人胰岛中MT1和MT2受体的细胞类型特异性密度，应在胰岛激素分泌的背景下考虑； ii）糖尿病对MT1和MT2密度的影响如下： iii）褪黑素对非糖尿病和2型糖尿病胰岛生长抑素分泌的不同影响。5 mmol / L葡萄糖。这些数据表明：i）人胰岛中MT1和MT2受体的细胞类型特异性密度，应在胰岛激素分泌的背景下考虑； ii）糖尿病对MT1和MT2密度的影响如下： iii）褪黑素对非糖尿病和2型糖尿病胰岛生长抑素分泌的不同影响。5 mmol / L葡萄糖。这些数据表明：i）人胰岛中MT1和MT2受体的细胞类型特异性密度，应在胰岛激素分泌的背景下考虑； ii）糖尿病对MT1和MT2密度的影响如下： iii）褪黑素对非糖尿病和2型糖尿病胰岛生长抑素分泌的不同影响。