Islet constitutive nitric oxide synthase and glucose regulation of insulin release in mice
Islet constitutive nitric oxide synthase and glucose regulation of insulin release in mice
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DOI：
10.1677/joe.0.1630039
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发表时间：
1999-10-01
影响因子：
4
通讯作者：
Lundquist, I
中科院分区：
文献类型：
--
作者：
Åkesson, B;Henningsson, R;Lundquist, I
本研究采用体外和体内相结合的方法，研究了一氧化氮合酶（NOS）选择性抑制剂n - g -硝基- l -精氨酸甲酯（L-NAME）对小鼠胰岛组成型一氧化氮合酶（NOS）活性的抑制作用与葡萄糖调节胰岛激素释放的关系。0.05或0.5 mM L-NAME对体外培养的胰岛细胞的cNOS活性没有明显影响，但5 mM L-NAME对其活性有明显抑制作用（-60%）。同样，葡萄糖刺激的胰岛素释放不受低浓度L-NAME的影响，但在5 mM NOS抑制剂的存在下大大增强。在培养的胰岛中，抑制cNOS活性导致在没有葡萄糖的情况下适度增强胰岛素释放，在生理或亚生理葡萄糖浓度下没有表现出任何影响，但在高血糖浓度下导致胰岛素释放明显增强。在缺乏葡萄糖的情况下，L-NAME抑制胰高血糖素的分泌。葡萄糖诱导的胰岛素释放和Ca-45（2+）外排的动力学表明，L-NAME引起胰岛素释放的立即增强，Ca-45（2+）外排略有增加。在K- atp（+）通道开启剂存在的30 mM K+去极化胰岛中，二氮氧化物、L-NAME仍能极大地增强葡萄糖诱导的胰岛素释放。最后，经L-NAME预处理的小鼠静脉注射葡萄糖后，胰岛素反应明显增强，葡萄糖耐量也有所改善。因此，注射L-NAME后直接离体分离的胰岛显示出明显降低的cNOS活性。总之，我们在这里首次证实，在体外和体内，由NOS抑制剂L-NAME诱导的胰岛cNOS活性的抑制，伴随着葡萄糖刺激的胰岛素释放的显著增强。NO抑制葡萄糖诱导的胰岛素释放的主要作用可能主要与Ca2+通量的变化无关，并且主要独立于膜去极化事件。
We have studied, by a combined in vitro and in vivo approach, the relation between the inhibitory action of N-G-nitro-L-arginine methyl ester (L-NAME), a selective inhibitor of nitric oxide synthase (NOS), on the activity of islet constitutive NOS (cNOS) and glucose regulation of islet hormone release in mice. The cNOS activity in islets incubated in vitro at 20 mM glucose was not appreciably affected by 0.05 or 0.5 mM L-NAME, but was greatly suppressed (-60%) by 5 mM L-NAME. Similarly, glucose-stimulated insulin release was unaffected by the lower concentrations of L-NAME but greatly enhanced in the presence of 5 mM of the NOS inhibitor. In incubated islets inhibition of cNOS activity resulted in a modestly enhanced insulin release in the absence of glucose, did not display any effect at physiological or subphysiological glucose concentrations, but resulted in a markedly potentiated insulin release at hyperglycaemic glucose concentrations. In the absence of glucose, glucagon secretion was suppressed by L-NAME. The dynamics of glucose-induced insulin release and Ca-45(2+) efflux from perifused islets revealed that L-NAME caused an immediate poten tiation of insulin release, and a slight increase in Ca-45(2+) efflux. In islets depolarized with 30 mM K+ in the presence of the K-ATP(+) channel opener, diazoxide, L-NAME still greatly potentiated glucose-induced insulin release. Finally, an i.v. injection of glucose to mice pretreated with L-NAME was followed by a markedly potentiated insulin response, and an improved glucose tolerance. In accordance, islets isolated directly ex vivo after L-NAME injection displayed a markedly reduced cNOS activity. In conclusion, we have shown here, for the first time, that biochemically verified suppression of islet cNOS activity, induced by the NOS inhibitor L-NAME, is accompanied by a marked potentiation of glucose-stimulated insulin release both in vitro and in vivo. The major action of NO to inhibit glucose-induced insulin release is probably not primarily linked to changes in Ca2+ fluxes and is exerted mainly independently of membrane depolarization events.