Glucose-dependent insulinotropic polypeptide-producing K cells in dexamethasone-treated rats

Investigation of the mechanisms contributing to the compensatory increase in insulin secretion during dexamethasone-induced insulin resistance in rhesus macaques

Dexamethasone has well-described effects to induce insulin resistance and increase insulin secretion. Herein, we examined potential contributors to the effect of dexamethasone to increase insulin secretion in rhesus macaques. Six male rhesus macaques received daily injections of either saline or dexamethasone (0.25 mg/kg i.m. for 7 days) in random order with 3 weeks between treatments. At the end of the treatment period, animals were fasted overnight and underwent a feeding study the next day, during which blood samples were taken before and for 60 min after a meal in order to assess islet hormone and incretin secretion. Dexamethasone induced marked increases in fasting plasma insulin, glucagon, leptin, and adiponectin concentrations (P<0.05). Surprisingly, the glycemic response after meal ingestion was decreased twofold during dexamethasone treatment (P<0.05). Dexamethasone-treated animals exhibited a significant increase in both insulin and glucose-dependent insulinotropic polypeptide (GIP) secretion during the feeding study (P<0.05). However, glucagon-like peptide-1 secretion was significantly lower in dexamethasone-treated animals compared with controls (P<0.01). Fasting and meal-stimulated pancreatic polypeptide concentrations (an index of the parasympathetic input to the islet) did not differ between saline and dexamethasone treatments. However, the proinsulin:insulin ratio was decreased throughout the feeding study with dexamethasone treatment suggesting an improvement of β-cell function (P<0.05). In conclusion, the maintenance of euglycemia and reduction of postprandial glycemia with short-term dexamethasone treatment appears to be due to the marked elevations of fasting and meal-stimulated insulin secretion. Furthermore, increases in postprandial GIP secretion with dexamethasone treatment appear to contribute to the effect of dexamethasone treatment to increase insulin secretion.

Cholecystokinin-producing (I) cells of intestinal mucosa in dexamethasone-treated rats

The aim of this study was to investigate the morphological, immunohistochemical and ultrastructural changes of cholecystokinin-producing (I) cells of gastrointestinal mucosa in dexamethasone-treated rats (D). After 12-daily intraperitoneal administration of 2mg/kg dexamethasone, rats developed diabetes similar to human diabetes mellitus type 2. The mean diameter of the duodenum was significantly decreased due to significant reduction of volume fraction and profile area of lamina propria. There was a decrease in volume fraction and number of cholecystokinin (CCK)-producing cells per mm(2) of mucosa, as well as their numerical density, but without statistical significance. Also, dexamethasone induced appearance of hyperactive duodenal I-cells with small number of granules and dilated endoplasmic reticulum. In conclusion, the present study showed that morphological changes in duodenum cholecystokinin-producing (I) cells occurred in diabetic rats, in a manner which, suggests compensatory effort of CCK cells in diabetic condition.