Effects of cyclosporin A and verapamil on mouse pancreatic islets

Functional and morphological study of cultured pancreatic islets treated with cyclosporine

Cyclosporine A (CsA), a potent immunosuppressive drug, has been found to induce glucose intolerance through its toxic effect on the endocrine pancreas. It is not exactly known whether CsA has a direct effect on the endocrine pancreas or induces its effect indirectly. The present study was therefore undertaken to examine the function and morphology of isolated pancreatic islets when they are directly exposed in vitro to CsA. Pancreatic islets were isolated from adult male Lewis rats using collagenase ductal perfusion technique. The islets were separated with the discontinuous Ficoll gradient technique and further purified by hand picking of the non-islet tissue. The islets were cultured in RPMI-1640, pH 7.4 and maintained at 37 degrees C in a humid atmosphere of 5% (v/v) carbon dioxide in air. Cyclosporine was added to the culture medium to give a final concentration of 1 microg/ml (therapeutic dose), 5 microg/ml (toxic dose), or vehicle (control). Islets were harvested at 1, 4 and 10 days of culture and processed for functional or histological study. The functional study of the islets cultured with 1 microg/ml CsA showed insulin and C-peptide contents similar to those of the control islets. The islets cultured with 5 microg/ml CsA showed a marked decrease in insulin and C-peptide contents. Glucose-dependent insulin release was variable. C-peptide release was lower than that of the control following both the therapeutic and toxic doses of CsA. Phase contrast microscopy showed that the islets cultured with 1 microg/ml CsA were mostly normal looking with a well-defined regular periphery; a few islets had ill-defined or irregular peripheries. The islets cultured with 5 microg/ml CsA had ill-defined irregular peripheries at 1 day, and were dense and forming clumps at 4 and 10 days following culture. There was a decrease in the islet number following the therapeutic dose; the decrease was more following the toxic dose of CsA. The islet diameters increased after the therapeutic dose, but slightly decreased following the toxic dose of CsA. Islets showed a weakly positive immunoperoxidase reaction for insulin that was weaker following the toxic dose of CsA. It is concluded that CsA has a direct effect on B-cells that was proved by the functional and morphological changes seen in the pancreatic islets cultured in vitro.

Disposition of a mixed meal by conscious dogs after seven days of treatment with cyclosporine A and prednisone

BACKGROUND

Combination immunosuppressive therapy, that often includes prednisone and cyclosporine A (CyA), is commonly used in the treatment of organ transplant patients. We hypothesized that CyA and prednisone treatment would alter the roles of the liver and peripheral tissues in the disposal of carbohydrates from a meal.

METHODS

Using the arteriovenous difference technique, we examined the disposition of an intragastrically delivered mixed meal in eight 24-hour fasted conscious dogs that had received CyA 15 mg x kg(-1) daily and prednisone 5 mg twice daily for 7 consecutive days before study (CyA-prednisone group). The results were compared with those from a group of 13 dogs (control group) receiving the same meal but no drugs.

RESULTS

Neither arterial blood glucose concentrations nor arterial plasma insulin or glucagon concentrations differed significantly between the groups at any time. Cumulative net gut glucose output was equivalent to 43 +/- 9 vs 57% +/- 7% of the glucose in the meal in CyA-prednisone vs control (p = .12). The CyA-prednisone group exhibited greater (p < .05) mean net hepatic glucose uptakes (15.4 +/- 4.6 vs 4.3 +/- 2.2 micromol x kg(-1) x min(-1) and net hepatic fractional extractions of glucose (7.8 +/- 1.6 and 1.5% +/- 1.0%) than the control group. Arterial blood lactate concentrations and net hepatic lactate output were greater in the CyA-prednisone group than the control group (p < .05). Hepatic glycogen content at the end of the study was 2.5-fold greater in the CyA-prednisone group than in the control group (p < .05). The nonhepatic tissues disposed of approximately 91% of the absorbed glucose in the control group but only approximately 26% in the CyA-prednisone group (p < .05).

CONCLUSIONS

CyA-prednisone treatment caused a marked shift in the carbohydrate disposal from a meal, enhancing the hepatic glucose uptake and decreasing peripheral glucose disposal.

Functional aspects of mouse islets transplanted to the kidney

To test whether the transplantation of pancreatic islets affects their basic functions, collagenase-isolated mouse islets were inserted under the left renal capsule of recipient animals. After various periods of time, grafts were removed from the kidney and examined for insulin content and secretory dynamics in a perifusion system. During syngeneic (C57BL/6, BALB/c) or subsyngeneic (NMRI) intrastrain transplantation, the graft insulin content fell drastically during the first week and stayed low for at least 6 weeks; first-phase secretion in general appeared suppressed. Immunosuppression by cyclosporin A had little effect on (sub)syngeneic grafts but markedly improved the performance of allotransplants. Daily injections of the calcium antagonist, verapamil, enhanced the insulin secretory responses of isolated grafts, whether (sub)syngeneic or allogeneic. In syngeneic and subsyngeneic grafts, the potentiating effect of acetylcholine on glucose-induced insulin release was markedly diminished, whereas that of caffeine was not. Transplanted islets also exhibited a subnormal responsiveness to the inhibiting action of noradrenaline. It is concluded that chronic denervation and transplantation of pancreatic islets may cause fundamental changes in the beta-cell responses to physiological regulators of insulin release.