Elevation of somatostatin content, and reduction of somatostatin release by GABA in rat pancreatic islets
Yoshioka, M.
Kobe Journal of Medical Sciences 32(1): 27-38
1986
ISSN/ISBN: 0023-2513 PMID: 2874261 Document Number: 281051
Gamma-aminobutyric acid (GABA) and somatostatin are present in high concentrations in the hypothalamus as well as in the pancreatic islets, while intraventricular GABA administration has been reported to increase the hypothalamic somatostatin content. The effect of GABA on somatostatin content of and release from the pancreatic islets was therefore investigated. Isolated pancreatic islets of Wistar rats were cultured at various concentrations of GABA and related substances for three days. The somatostatin content of the islets was significantly higher in the presence than in the absence of GABA. The somatostatin release from islets in the presence of GABA decreased significantly from the level in the absence of GABA. Neither insulin and glucagon content nor their release were influenced by GABA. GABA concentration of the islets was increased in the presence of 100.mu.M .gamma.-vinyl GABA or 10.mu.M AOAA in the medium, whereas somatostatin content was not affected. The GABA agonist muscimol (1.0 and 0.1.mu.M) also increased the somatostatin content and decreased the release. This elevated somatostatin content in the islets induced by GABA was reduced to the original level by the addition of 1.0.mu.M bicuculline, a GABA antagonist. These observations suggest that GABA in the pancreatic islets changes the somatostatin content and release, possibly through a GABA receptor on D cells of the islets.