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We evaluated the effect of immunosuppressive concentrations of cyclosporin A (CsA), given intramuscularly, on the levels of glucose, insulin, C-peptide, glucagon, pancreatic polypeptide (PP), lactate, alanine and beta-hydroxy-butyrate in a group of pancreatectomized mongrel dogs with intrasplenic islet autografts, given mixed meal and oral glucose, while on or off CsA therapy. In whole blood, HPLC-measured drug levels ranged from 412 to 803 ng/ml. Basal glucose and insulin concentrations did not differ significantly between non-pancreatectomized, control dogs and transplanted animals, whether on or off CsA. After the meal challenge, glucose levels were significantly higher in transplanted animals than in normal dogs, and no additional deleterious effect of CsA was observed. Similar insulin and C-peptide responses were found in animals either on or off CsA treatment. Fasting and post-meal concentrations of glucagon, PP and intermediate metabolites were not affected by the drug. These results suggest that intramuscular CsA, given at doses known to sustain islet allograft function, has no detrimental effect on the hormonal and metabolic responses to mixed meal and oral glucose in dogs with intrasplenic islet autografts.

Few data have been published so far on the long-term metabolic and endocrine consequences of intrasplenic islet autografts in dogs and the available information mainly deals with glucose response and, more rarely, insulin secretion during intravenous glucose tolerance tests. The effect of islet transplantation on glucagon levels has never been reported. In this study we measured glucose, insulin, total glucagon, and pancreatic glucagon in dogs before and after (up to 1 year) intrasplenic islet autografts. Pancreata were retrieved from 21 adult dogs and the islets were isolated by collagenase digestion. The endocrine tissue was transplanted into the spleen by direct pulp injection. Autografts resulted in normoglycaemia in 19 out of 21 dogs (90%). Among the successfully transplanted dogs, the percentage of functioning grafts was 71% at 1 year. The metabolic and hormonal results of the follow-up showed that fasting glucose and insulin concentrations did not differ significantly before and after transplantation. However, glucose tolerance and insulin secretion on intravenous glucose tolerance testing were significantly reduced in transplanted animals. Fasting total and pancreatic glucagon, and their integrated releases during the test did not change significantly after islet transplantation. These results demonstrate that: 1) long-term function of intrasplenic canine islet autografts can be achieved in high percentages; 2) autotransplanted animals have normal or near normal fasting glucose and insulin levels, but reduced glucose disappearance and insulin secretion on intravenous glucose tolerance tests; 3) normal glucagon secretion is a feature of successful islet grafts.

Azathioprine-prednisone immunosuppression has proven ineffective in rodent, canine, and human islet transplantation. ALS has demonstrated beneficial effects in rodent islet transplantation, but high dose CsA monotherapy remains the most effective immunosuppressive modality in canine islet allotransplantation. Nephrotoxicity prevents effective utilization of such an approach in human islet transplantation. We have been unable to demonstrate additional benefit from the addition of azathioprine and prednisone to CsA immunosuppression in large animal islet allotransplantation. CsA, azathioprine and prednisone all appear to have the potential for adverse effects variously on islet engraftment, insulin secretion, and/or peripheral insulin activity. The effects of CsA appear to be dose related and may be reversible. Our approach in clinical islet transplantation has been to achieve potent induction immunosuppression with Minnesota antilymphocyte globulin, delayed CsA administration, and ongoing maintenance with low dose triple immunotherapy. Initial results are encouraging.

The extrahepatic diversion of essential splanchnic hepatotrophic factors may cause the liver atrophy and insufficiency that follows portacaval shunting. To investigate this, control dogs with end-to-side portacaval shunts (control-PCS, n = 6) were compared with dogs shunted 1 month after intraportal pancreatic islet autotransplantation (islet-Tx-PCS, n = 5). From the distal pancreas of each experimental dog, 1.95 +/- 0.49 X 10(5) islets were isolated by collagenase digestion and retransplanted within 3 hours. Assays of hepatocellular function (caffeine clearance) and hepatic blood flow (indocyanine green), conventional biochemical liver function tests, and glucose, insulin, and glucagon responses to intravenous glucose challenge were measured monthly and when dogs were killed. Four of six control-PCS dogs were killed 32 +/- 9 days after shunting because of more than 20% body weight loss; one control-PCS dog lost only 7% of body weight by day 56 and stabilized. No significant loss of body weight occurred in islet-Tx-PCS dogs (n = 5). Liver function test abnormalities seen in control-PCS dogs were absent in islet-Tx-PCS dogs. Both control-PCS and islet-Tx-PCS indocyanine green half-life measurements were significantly (p less than 0.05) prolonged at all times, indicating equally reduced hepatic blood flow after shunting for both groups. In contrast, islet-Tx-PCS caffeine half-life periods were significantly (p less than 0.05) shorter than in control-PCS dogs and were similar to those in normal dogs, indicating a protective effect of the transplanted islets on hepatocellular function. We conclude that intraportal pancreatic islet autotransplants prevent, by the local release of hepatotrophic factors within the liver, the metabolic abnormalities and loss of hepatic function after PCS.