Glucose stimulates somatostatin secretion in pancreatic δ-cells by cAMP-dependent intracellular Ca2+ release.

Somatostatin secretion from pancreatic islet δ-cells is stimulated by elevated glucose levels, but the underlying mechanisms have only partially been elucidated. Here we show that glucose-induced somatostatin secretion (GISS) involves both membrane potential-dependent and -independent pathways. Although glucose-induced electrical activity triggers somatostatin release, the sugar also stimulates GISS via a cAMP-dependent stimulation of CICR and exocytosis of somatostatin. The latter effect is more quantitatively important and in mouse islets depolarized by 70 mM extracellular K+ , increasing glucose from 1 mM to 20 mM produced an ∼3.5-fold stimulation of somatostatin secretion, an effect that was mimicked by the application of the adenylyl cyclase activator forskolin. Inhibiting cAMP-dependent pathways with PKI or ESI-05, which inhibit PKA and exchange protein directly activated by cAMP 2 (Epac2), respectively, reduced glucose/forskolin-induced somatostatin secretion. Ryanodine produced a similar effect that was not additive to that of the PKA or Epac2 inhibitors. Intracellular application of cAMP produced a concentration-dependent stimulation of somatostatin exocytosis and elevation of cytoplasmic Ca2+ ([Ca2+]i). Both effects were inhibited by ESI-05 and thapsigargin (an inhibitor of SERCA). By contrast, inhibition of PKA suppressed δ-cell exocytosis without affecting [Ca2+]i Simultaneous recordings of electrical activity and [Ca2+]i in δ-cells expressing the genetically encoded Ca2+ indicator GCaMP3 revealed that the majority of glucose-induced [Ca2+]i spikes did not correlate with δ-cell electrical activity but instead reflected Ca2+ release from the ER. These spontaneous [Ca2+]i spikes are resistant to PKI but sensitive to ESI-05 or thapsigargin. We propose that cAMP links an increase in plasma glucose to stimulation of somatostatin secretion by promoting CICR, thus evoking exocytosis of somatostatin-containing secretory vesicles in the δ-cell.

Effect of mica monomer powder on chief and parietal cells as well as G and D cells in gastric mucosa of chronic atrophic gastritis in rats.

OBJECTIVE: To study the regulative action of mica monomer powder preparation on the chief and parietal cells as well as G and D cells in the gastric mucosa of the experimental atrophic gastritis (CAG) rats. METHODS: Intervention therapy was given to the experimental CAG rats at three different doses of mica monomer powder preparation to evaluate the changes of chief and parietal cells as well as G and D cells in the gastric mucosa and the histopathological changes of gastric mucosa. RESULTS: Mica monomer powder preparation at three different doses could increase the amount of chief and parietal cells as well as G and D cells in gastric mucosa of the experimental CAG rats and alleviate and control the inflammation of gastric mucosa and the atrophy of gastric mucosa glands. Especially, better effects were shown in the mid and high dose groups. CONCLUSION: Mica has the pharmacological action of protecting the gastric mucosa, enhancing blood flow of the gastric mucosa, and consequently improving the inflammatory responses of the gastric mucosa. One of the mechanisms is associated with promoting the secretion of gastric acid and gastric pepsin and regulating the neuroendocrine mechanism including gut hormone secretion (gastrin and somatostatin) by increasing the number of chief and parietal cells as well as G and D cells.

[Effect of mica monomer granule on gastrin, somatostatin and G cells as well as D cells of gastric mucosa in CAG rat].

OBJECTIVE: To study regulative action of mica monomer granule preparation on gastrin (GAS), somatostatin (SS) and G cells as well as D cells of gastric mucosa in experimental chronic atrophic gastritis (CAG) rat. METHOD: CAG rats were treated with mica monomer granule preparation with three different dosages--high, moderate and low level respectively. Changes of blood serum GAS, blood plasma SS and G cells as well as D cells of gastric mucosa in CAG rats were observed and detected with ELISA method, RIA method and immunocytochemistry method. RESULT: Mica monomer granule of three different dosages could increase the quantity of G cells as well as D cells of gastric mucosa and the concentration of blood serum GAS and decrease the content of blood plasma SS in CAG rat at different level respectively. It was more effective in high and moderate dosage groups. CONCLUSION: Mica has the pharmacological action of protecting gastric mucosa, promoting the palingenesis of gastric gland and enhancing blood stream of gastric mucosa consequently to abate the inflammation reaction of gastric mucosa. Its effective mechanism is associated with the neuroendocrine regulative mechanism of promoting the secretion of gastric acid and gastric pepsin by increasing the amount of G cells as well as D cells and the concentration of blood serum GAS, and reducing inhibiting action on GAS secretion and enhancing the secretion of GAS by decreasing the content of SS.

Effects of Momordica charantia fruit juice on islet morphology in the pancreas of the streptozotocin-diabetic rat.

An investigation was made of the effect of Momordica charantia fruit juice on the distribution and number of alpha, beta and delta cells in the pancreas of streptozotocin (STZ)-induced diabetic rats using immunohistochemical methods. The results indicated that there was a significant (Student's t-test, P < 0.004) increase in the number of beta cells in M. charantia-treated animals when compared with untreated diabetics, however, their number was still significantly less than that obtained for normal rats. There was also a significant (P < 0.006) increase in the number of delta cells in STZ-diabetic rats compared to non-diabetic rats. This increase in the number of delta cells was not affected by M. charantia treatment. The number of alpha cells did not change significantly in M. charantia-treated rats when compared with untreated diabetic rats. Our results suggest that oral feeding of M. charantia fruit juice may have a role in the renewal of beta cells in STZ-diabetic rats or alternately may permit the recovery of partially destroyed beta cells.