Studies on physiological function of GAD and GABA in pancreatic islet

本文通过比较胰岛和中枢神经组织GABA水平对影响GABA脱羧酶（GABA脱羧酶，GAD）及其代谢酶GABA转氨酶（GABA-T）的药物的反应性，以及某些胰岛素释放刺激剂对胰岛GAD水平的影响，研究了胰岛中GABA脱羧酶（GAD）及其合成GABA的生理功能。(1)体内研究（a）将已知可抑制中枢神经组织中GAD的3-巯基丙酸腹膜内给予Wistar大鼠，可降低海马、下丘脑、上级丘和纹状体以及胰岛中的GABA含量。(b)已知可抑制中枢神经组织中GABA-T的丙戊酸钠类似注射可升高所有上述组织中的GABA含量。(2)体外研究（a）用3-巯基丙酸或丙戊酸钠孵育分离的Wistar大鼠胰岛分别降低或增加胰岛中的GABA含量。(b)用Western印迹法测得的GAD水平在不刺激胰岛素合成的精氨酸作用下没有变化，而在刺激胰岛素合成的葡萄糖作用下则有所增加，这表明GAD与GABA-T在中枢神经组织和胰岛间的药理学反应方面明显相似，胰岛中的GAD似乎在胰岛素合成中起作用。

The physiological function of gamma-aminobutyric acid (GABA) decarboxylase (GAD) and its synthesizing GABA in pancreatic islets is studied by comparing the GABA level of islets with that of central nervous tissues in terms of responsiveness to drugs affecting GAD and GABA transaminase (GABA-T) , a metabolizing enzyme of GABA,and by observing the effect of some insulin release stimulators on GAD level in islets.(1) Studies in vivo(a) The intraperitoneal administration of 3-mercaptopropionic acid known to suppress GAD in central nervous tissues into Wistar rats decreased the GABA content in the hypocampus, hypothalamus, superior colliculus and striatum as well as in islets.(b) The similar injection of sodium valproate known to suppress GABA-T in central nervous tissues raised the GABA content in all abovementioned tissues.(2) Studies in vitro(a) Incubation of isolated Wistar rat islets with 3-mercaptopropionic acid or sodium valproate decreased or increased the GABA content in the islets respectively.(b) GAD level measured with Western blot in islets did not change by arginine which does not stimulate insulin synthesis but increased by glucose which stimulates insulin synthesis.These observations indicate that GAD as well as GABA-T are apparently similar in terms of pharmacological response between the central nervous tissues and the islets, and that the GAD in islets seems to play a role in insulin synthesis.