Effects of portacaval anastomosis on pancreatic islets of the rat

Congenital intrahepatic portocaval shunts and hypoglycemia due to secondary hyperinsulinism: a case report and review of the literature

Background

Congenital portosystemic shunts present with various associated complications, such as other congenital malformations, hyperammonemia, or hepatopulmonary syndrome. Few cases of associated hypoglycemia have been reported so far and our case, to the best of our knowledge, describes the most severe extent of hypoglycemia.

Case presentation

We describe the case of a newborn Arab boy with two intrahepatic portosystemic shunts, resulting in severe and persistent hypoglycemia, due to which one of the shunts was closed by interventional radiology whereas the other shunt had already closed spontaneously.

Conclusions

Because he showed elevated levels for insulin and prolonged high insulin levels in an oral glucose tolerance test, our case supports the theory that portocaval shunts cause a reduced hepatic insulin reduction due to the high blood volume bypassing the liver. This case provides further insights into glucose regulation mechanisms of the liver and we suggest a consistent screening for hypoglycemia in patients with congenital portosystemic shunts.

Control of Insulin Secretion and Glucose Homeostasis in Exercising Diabetic Rats with Intrasplenic or Kidney Subcapsular Islet Grafts

This study was designed 1) to investigate mechanisms of insulin secretion during exercise after transplantation of islets in the spleen and under the kidney capsule, and 2) to compare these organs as transplantation site regarding an adequate portal or systemic delivery of insulin and glucose homeostasis during exercise. Diabetic rats were provided with 5 μL isogenic islet tissue in the spleen or under the kidney capsule, which results in normoglycemia, and were submitted to a swimming test Portal plasma insulin levels were higher than simultaneously sampled systemic insulin levels in the control and in the intrasplenic islet grafted group, but not in the kidney subcapsular islet-grafted group. Plasma portal and systemic insulin levels decreased, and glucose levels increased during exercise in all groups. The exercise-induced increase in levels of catecholamines was larger in systemic than in portal plasma, suggesting catecholamine extraction by the lungs or intestines. The experiments were repeated after removing of adrenal medulla, resulting in nondetectable or very low plasma adrenaline levels. Despite these low adrenaline levels, insulin levels decreased during exercise. The results indicate that 1) the exercise-induced reduction of insulin secretion is not mediated by circulating adrenaline, but is probably under control of the sympathetic nervous system, which could be the result of reinnervation of the transplanted islets. 2) Although a portal-systemic insulin gradient was absent in rats with kidney subcapsular islet grafts, the absence of a difference in glucose homeostasis during exercise between the sites revealed that all investigated sites are preferential to transplant islets.

The effect of portacaval anastomosis on the expression of glutamine synthetase and ornithine aminotransferase in perivenous hepatocytes

There is functional zonation of metabolism across the liver acinus, with glutamine synthetase restricted to a narrow band of cells around the terminal hepatic venules. Portacaval anastomosis, where there is a major rerouting of portal blood flow from the portal vein directly to the vena cava bypassing the liver, has been reported to result in a marked decrease in the activity of glutamine synthetase. It is not known whether this represents a loss of perivenous hepatocytes or whether there is a specific loss of glutamine synthetase. To answer this question, we have determined the activity of glutamine synthetase and another enzyme from the perivenous compartment, ornithine aminotransferase, as well as the immunochemical localization of both glutamine synthetase and ornithine aminotransferase in rats with a portacaval shunt. The portacaval shunt caused a marked decrease in glutamine synthetase activity and an increase in ornithine aminotransferase activity. Immunohistochemical analysis showed that the glutamine synthetase and ornithine aminotransferase proteins maintained their location in the perivenous cells. These results indicate that there is no generalized loss of perivenous hepatocytes, but rather, there is a significant alteration in the expression of these proteins and hence metabolism in this cell population.

[Morphometric and immunohistochemical patterns of duodenal CCK-cells in rats with portacaval shunts]

INTRODUCTION

End-to-side portacaval shunt (PCS) performed in rats is an appropriate experimental model of chronic liver insufficiency. Functional hepatic injury followed by numerous metabolic and endocrine disorders develops, as well. Due to impaired functional hepatic activity in PCS and to the well known role of the liver in CCK metabolism and elimination, delayed CCK bloodstream elimination may be responsible for increased CCK-A receptor activity. Therefore, we investigated immunohistochemical and morphometric features of duodenal CCK-cells in rats with PCS.

MATERIAL AND METHODS

Male Wistar rats (180 - 250g body weight) were used in this experiment. The animals were divided into two groups: PCS-animals (experimental group (n=27) which underwent an operation) and C - unoperated animals [control group (n=11)].

SURGICAL TECHNIQUE

End-to-side portacaval anastomosis was created using the technique of Lee and Fisher, modified by Bismuth et al. Eight weeks, after the operation, animals were sacrificed. Pancreatic and hepatic weights were measured and samples taken from appropriate segments of the small intestine were used for morphometric and immunohistochemical CCK-cells determination. IMMUNOHISTOCHEMICAL TECHNIQUE: Peroxidase-antiperoxidase (PAP) technique described by Stenberger was applied for detection of intestinal CCK-immunoreactive cells.

RESULTS

Our results indicate that eight weeks after operation liver weight was reduced in animals with PCS compared to control animals (p<0.01). To the contrary, in comparasion with control animals, the pancreatic wight was increased (p<0.01). In the exocrine pancreas of rats with PCS there were lipid droplets and hypertrophy of the acinus cells. The morphometric analysis of CCK-immunoreactive cells in different small intestine segments indicates that in the duodenum of animals with PCS there was a significant cell increase compared to control, unoperated animals.

CONCLUSION

In liver cirrhosis, plasma CCK-8 concentration increases. In PCS, performed in rats, as an experimental model of chronic liver insufficiency, proliferation of CCK-cells in the small intestine leads to pancreatic hypertrophy and hyperplasia.

Some metabolic and endocrine consequences in portacaval-shunted rats

Some metabolic and endocrine consequences of portacaval shunt were examined in rats eight weeks after the operation. Plasma levels of insulin, glucagon somatostatin, such as pancreatic content of insulin, glucagon, and somatostatin were determined by radioimmunoassay. Numerous biochemical parameters, such as the concentration of serum ammonia, transaminase (AST and ALT), urea bilirubin, total plasma protein and plasma albumin levels were determined by standard biochemical tests. Normal plasma levels of insulin and somatostatin hyperglucagonaemia were observed in rats with portacaval shunt. After portacaval shunt there was a highly significant increase (p<0.01) in levels of blood ammonia, AST and ALT. Serum fasting glucose levels were significantly lower in portacaval shunt rats (p<0.01) in comparison to controls and sham operated rats. We conclude that the metabolic and endocrine consequences of portacaval shunt in rats are probably related to the functional deterioration of the liver due to diversion of the portal blood in systemic circulation.

Rats with portal-caval vein transposition show hyperinsulinemia and insulin resistance

To compare the metabolic effects of portal and systemic delivery of insulin, we used portal-caval transposition (PCT) in rats to provide total systemic diversion of splanchnic venous blood. PCT rats exhibited normal weight gain, liver histology, liver-function tests, glycosylated hemoglobin, arterial blood pressure, and hepatic blood flow. Mean liver weight relative to body weight was 12% lower in PCT rats than in sham-operated control (CTR) rats 30 days following transposition. Indwelling venous catheters were established to facilitate metabolic studies in conscious, minimally restrained animals. Postabsorptive plasma glucose and C-peptide (CPEP) levels were similar in PCT and CTR rats; however, postabsorptive immunoreactive insulin (IRI) levels were elevated in PCT rats (67 +/- 3.1 v 49 +/- 3.5 pmol.L-1, P < .002, n = 11 v 11), as were postabsorptive plasma glucagon levels (570 +/- 67 v 240 +/- 11 ng.L-1, P < .001, n = 11 v 16) at similar body weights. The postabsorptive CPEP/IRI concentration ratio was lower in PCT than in CTR rats (4.0 +/- 0.3 v 6.0 +/- 0.6, P < .02), suggesting reduced hepatic extraction of insulin. Insulin sensitivity (IS), determined by minimal model analysis of frequently sampled intravenous glucose tolerance tests yielding the sensitivity index (SI), was reduced in PCT compared with CTR (61 +/- 5.6 v 86 +/- 9.0 (mumol.L-1)-1.min-1, P < .04, n = 9 v 10). During euglycemic-hyperinsulinemic clamps, glucose infusion rates (GIRs) from 60 to 120 minutes were lower in PCT than in CTR rats (6.0 +/- 0.3 v 8.0 +/- 0.4 g.kg-1.min-1, P < .002, n = 9 v 7) with matching plasma IRI levels, confirming the reduced IS in PCT rats. Areas under the concentration curves ([AUCs] 0 to 150 minutes) for glucose tolerance tests (gavage) indicated that plasma glucose excursion was similar in PCT and CTR rats whereas AUC IRI was significantly higher in PCT than in CTR rats (23 +/- 1.3 v 18 +/- 0.6 nmol.L-1.min, P < .009, n = 11 v 11). However, AUC CPEP for oral glucose tolerance tests was lower in PCT than in CTR rats (55 +/- 3.4 v 68 +/- 4.8 nmol.L-1.min, P < .05), indicating decreased insulin secretion. Thus, the mean ratio AUC CPEP/AUC IRI was significantly lower in PCT rats (2.5 +/- 0.2 v 3.8 +/- 0.3, P < .002), again suggesting reduced hepatic extraction of insulin. Thus, euglycemia after PCT was accompanied by elevated postabsorptive and glucose-stimulated levels of IRI in systemic blood, postabsorptive hyperglucagonemia, and decreased insulin secretion in response to glucose challenge (gavage), with diminished hepatic extraction of insulin and decreased IS. The PCT model illustrates the insulin-resistant adaptive state that results from systemic delivery of insulin, and indicates the importance of hepatic portal delivery of insulin and possibly of other gastroenteropancreatic hormones in the maintenance of IS and physiological metabolic control.