| Summary: | 博士 === 國立屏東科技大學 === 食品科學系所 === 106 === Morin is an active principle contained in guava that is a popular fruit used to against diabetes in Taiwan. Morin has been documented to attenuate hyperglycemia via insulin secretion. However, the potential mechanism(s) for morin induced insulin secretion remained obscure. Therefore, the present study is designed to find out the possible mechanism(s). At first, the Chinese Hamster ovary (CHO) cells transfected imidazoline receptor (I-R) gene were used to treat with morin. Morin induced a dose-dependent increase in intracellular calcium ions (Ca2+) in cells expressing I-R but not in cells without I-R gene. Activation of I-R by morin can thus be considered. Then, a cultured pancreatic cell line, Min-6 cells, was applied to treat morin and a dose-dependent increase in insulin secretion was observed in parallel with an increase in Ca2+.
Both effects induced by morin were markedly reduced in Min-6 cells received siRNA specific to I-R supporting the activation of I-R by morin. Moreover, both effects of morin were also inhibited by antagonist specific to I-3R. Activation of I-3R by morin was further identified using the blocker of phospholipase C (PLC) that is coupled with I-3R. Interestingly, using the glucose-stimulated insulin secretion (GSIS) method, insulin secretion was influenced by glucose in medium. However, the ratio of insulin secretion induced by morin was the same between low glucose and high glucose conditions. It means that activation of I-3R seems not regulated by glucose in Min-6 cells. Otherwise, similar results were also characterized in isolated pancreatic islets indicating morin can activate I-3R to induce insulin secretion. Additionally, morin induced reduction of hyperglycemia or increased insulin secretion was observed in diabetic rats and both effects were also inhibited by antagonist specific to I-3R. Plasma C-peptide, a marker secreted with insulin from pancreatic islets, was also changed in same manner. Therefore, effect of morin on pancreatic I-3R to enhance insulin secretion has been characterized. Taken together, the in vitro and in vivo results suggest a new finding that morin can activate I-3R in pancreatic islets to enhance insulin secretrion via PLC and Ca2+ signaling pathway.
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