Plasma glucagon responses to insulin-induced hypoglycemia and arginine in spontaneous non-insulin-dependent diabetes mellitus (NIDDM) rats, Otsuka Long Evans Tokushima Fatty (OLETF) strain

Activated perilobular, not periacinar, pancreatic stellate cells contribute to fibrogenesis in chronic alcoholic pancreatitis

The authors investigated the role of activated perilobular, not periacinar, pancreatic stellate cells, in fibrogenesis in chronic pancreatitis, based on the distribution of myofibroblasts. Twenty-four patients with clinically diagnosed chronic alcoholic pancreatitis were studied histopathologically, immunohistochemically and quantitatively. In all cases, fibrosis was patchily distributed in the perilobular, or interlobular, areas, accompanied by a cirrhosis-like appearance; it had extended into the intralobular area in advanced cases. Seven patients had a massive or confluent loss of exocrine tissue, resulting in extensive interlobular fibrosis; the more extensive the interlobular fibrosis, the smaller the lobules. Immunoreactivity to alpha-smooth muscle actin, a myofibroblast marker, was found mostly in the same areas of the fibrosis, mainly the interlobular, and less often the periacinar, areas; the average percentage area of perilobular myofibroblasts was significantly higher than that of periacinar myofibroblasts in 20 randomly selected lobules (P > 0.001), in which the average value for the former was 38.03% (range: 13.54-61.32%; SD, 13.8%) and that for the latter was 4.85% (range 0.90-9.57%; SD, 2.22%). Fibrosis also immunostained positive for collagen types I and III. In conclusion, activated perilobular, not periacinar, pancreatic stellate cell contribute to fibrogenesis in chronic pancreatitis.

Immunohistochemical analysis of cholecystokinin A receptor distribution in the rat pancreas

Cholecystokinin (CCK) plays a major role in the regulation of pancreatic enzyme secretion based on its binding to the CCK-A receptor (CCK-AR). While CCK-AR is known to be expressed in rat islet B cells, the localization of CCK-AR in rat pancreatic A and D cells remains poorly understood. The aim of this study was to identify the localization of CCK-AR in rat pancreatic islets by means of double immunofluorescence straining with antibodies against CCK-AR, glucagon, insulin and somatostatin and with in situ hybridization to detect its transcript. CCK-AR-like immunoreactive cells were found to overlap both with glucagon-like immunoreactive cells and insulin-like immunoreactive cells but not with somatostatin-like immunoreactive cells. An in situ hybridization study using a cRNA probe for CCK-AR revealed that CCK-AR mRNA was expressed in the center and periphery of the pancreatic islets. Further to this, immunofluorecsence staining using anti-glucagon antibody was carried out after in situ hybridization using the CCK-AR cRNA probe in order to identify CCK-AR mRNA expressing cells. CCK-AR mRNA exhibited a distribution pattern almost identical to that of glucagon-like immunoreactive cells. These results show clearly that CCK-AR exists not only in B but also in A cells of the rat pancreas, suggesting that CCK regulates the secretion of insulin and glucagon at least partly via CCK-AR.

Downregulation of the skeletal muscle pyruvate dehydrogenase complex in the Otsuka Long-Evans Tokushima Fatty rat both before and after the onset of diabetes mellitus

The pyruvate dehydrogenase complex (PDC) catalyzes the irreversible oxidative decarboxylation of pyruvate in mitochondria. The PDC activity is regulated by a phosphorylation/dephosphorylation cycle catalyzed by specific kinases (PDK) and phosphatases (PDP). In this study, the regulatory mechanisms of PDC were examined in skeletal muscle of the spontaneously diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rat before and after the onset of diabetes. The Long-Evans Tokushima Otsuka (LETO) rat was used as control. Plasma glucose and insulin concentrations were at normal levels in both groups at 8 weeks of age but were significantly higher in OLETF than in LETO rats at 25 weeks of age (1.2-fold for glucose and 15-fold for insulin), indicating development of diabetes in the former. Plasma free fatty acids were 1.6-fold concentrated and the skeletal muscle PDC activity state was significantly lower in OLETF than in LETO rats at both ages, suggesting suppression of pyruvate oxidation in OLETF rats even before the onset of diabetes. The PDK activity and the abundance of the PDK isoform 4 protein as well as mRNA were greater in OLETF rats at both ages. Conversely, the abundance of the PDP isoform 1 protein and mRNA was less in OLETF than in LETO rats at both ages. These results suggest that concomitant greater PDK4 and less PDP1 expression in skeletal muscle of OLETF rats before the onset of diabetes are responsible for the lowering of the PDC activity and may be related with the development of diabetes mellitus.

Histopathologic difference between chronic pancreatitis animal models and human chronic pancreatitis

OBJECTIVES

There are many experimental models for chronic pancreatitis. However, it remains unclear which animal models of pancreatic fibrosis can be categorized as chronic pancreatitis models. We compared the histologic features of some animal models of pancreatic fibrosis/chronic pancreatitis and chronic pancreatitis in humans.

METHODS AND RESULTS

Human chronic pancreatitis due to chronic alcohol abuse and unknown etiology showed interlobular fibrosis and a cirrhosis-like appearance. Histopathologically, spontaneous pancreatitis models, WBN/Kob rats and OLETF rats, showed localized/nodular fibrotic lesions, which consisted of swollen, aggregated, atrophic islets of Langerhans; loss of the exocrine parenchyma and hemosiderin deposition that was seldom distributed in the interlobular area. On the other hand, fibrosis in the canine model, which was produced by combining alcohol administration with incomplete pancreatic duct obstruction, was characterized by interlobular fibrosis admixed with a cirrhosis-like appearance very similar to that in human chronic pancreatitis.

CONCLUSION

Most experimental models for chronic pancreatitis, except alcohol administration combined with other procedures such as incomplete pancreatic duct obstruction, are different from human chronic pancreatitis.

Changes in islet capillary angioarchitecture coincide with impaired B-cell function but not with insulin resistance in male Otsuka-Long-Evans-Tokushima fatty rats: dimorphism of the diabetic phenotype at an advanced age

The Otsuka-Long-Evans-Tokushima fatty (OLETF) rat is a genetic model of spontaneous development of non-insulin-dependent diabetes mellitus (NIDDM) established as an inbred strain after 20 generations of selective breeding. Although they are thought to be genetically homogeneous, they show a dimorphism regarding the diabetic phenotype at an advanced age, with one remaining obese and modestly diabetic while the other becomes lean and overtly diabetic. To clarify the causes for this divergence, we examined the physical, biochemical, and histopathological features in rats at 50 weeks of age, including an analysis of islet angioarchitecture. Sixty-one of 85 male OLETF rats lost weight, while the remainder remained obese. Mean nonfasting plasma glucose in the lean group was 21.8+/-4.6 mmol/L, significantly higher versus the obese group (10.5+/-1.4 mmol/L) and the age-matched control Long-Evans-Tokushima-Otsuka (LETO) group (7.1+/-0.6 mmol/L). Morphological studies of the pancreas from the lean group showed enlarged multilobulated fibrotic islets with a paucity of B cells, whereas islets from the obese group appeared slightly enlarged and showed a relative abundance of B cells. The fine capillaries that form a network in the islets were extremely sparse in the lean group, resulting in a defective glomerular-like configuration, whereas those from the obese group were dense, forming a nearly typical glomerular-like configuration. Increased plasma insulin responses to oral and intravenous (i.v.) glucose and i.v. glucagon loads were nearly absent in the lean group, while they were evident in the obese group, although to a lesser extent compared with the LETO group. Mean insulin secretory output from the perfused pancreas in response to 11.1 mmol/L glucose in the lean group (3.5+/-2.2 pmol/20 min) was significantly lower versus the obese group (8.8+/-6.5 pmol/20 min) and LETO group (22.0+/-10.8 pmol/20 min). Similarly, pancreatic insulin content was significantly lower in the lean group (9.3+/-6.1 microg) versus the others (26.1+/-17.3 microg for obese and 41.1+/-24.8 microg for LETO). In vivo insulin-stimulated glucose uptake measured by a euglycemic clamp technique was significantly higher in the lean group compared with the obese group. These results demonstrate that the dimorphism regarding the diabetic phenotype in male OLETF rats at 50 weeks of age was due to differences in the number of islet B cells, which could be the result of a variation in the capacity for B-cell proliferation among male OLETF rats.

The cholecystokinin-A receptor mediates inhibition of food intake yet is not essential for the maintenance of body weight

Food intake and body weight are determined by a complex interaction of regulatory pathways. To elucidate the contribution of the endogenous peptide cholecystokinin, mice lacking functional cholecystokinin-A receptors were generated by targeted gene disruption. To explore the role of the cholecystokinin-A receptor in mediating satiety, food intake of cholecystokinin-A receptor-/- mice was compared with the corresponding intakes of wild-type animals and mice lacking the other known cholecystokinin receptor subtype, cholecystokinin-B/gastrin. Intraperitoneal administration of cholecystokinin failed to decrease food intake in mice lacking cholecystokinin-A receptors. In contrast, cholecystokinin diminished food intake by up to 90% in wild-type and cholecystokinin-B/gastrin receptor-/- mice. Together, these findings indicate that cholecystokinin-induced inhibition of food intake is mediated by the cholecystokinin-A receptor. To explore the long-term consequences of either cholecystokinin-A or cholecystokinin-B/gastrin receptor absence, body weight as a function of age was compared between freely fed wild-type and mutant animals. Both cholecystokinin-A and cholecystokinin-B/gastrin receptor-/- mice maintained normal body weight well into adult life. In addition, each of the two receptor-/- strains had normal pancreatic morphology and were normoglycemic. Our results suggest that although cholecystokinin plays a role in the short-term inhibition of food intake, this pathway is not essential for the long-term maintenance of body weight.

Influence of highly purified eicosapentaenoic acid ethyl ester on insulin resistance in the Otsuka Long-Evans Tokushima Fatty rat, a model of spontaneous non-insulin-dependent diabetes mellitus

We investigated the effect of long-term administration of highly purified eicosapentaenoic acid ethyl ester (EPA-E), an n-3 polyunsaturated fatty acid derived from fish oil, in comparison to the effects of lard, olive oil, safflower oil, or distilled water as the control on the development of insulin resistance in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of spontaneous non-insulin-dependent diabetes mellitus (NIDDM) with obesity. After 17 or 18 weeks of treatment, the glucose infusion rate (GIR) in the euglycemic insulin-glucose clamp test only showed a significant increase in EPA-E-treated rats compared with control rats given distilled water alone as the vehicle. The GIR in EPA-E-treated animals was approximately three times greater than in the controls. This is the first report to display the influence of various fatty acids on the development of insulin resistance in OLETF rats. We demonstrated that EPA-E prevents the onset of insulin resistance, whereas olive oil and safflower oil have no effect and lard exacerbates insulin resistance. Fatty acid analysis of phospholipids in skeletal muscle showed a significant increase of the C18:2, C20:5, and C22:5 components in EPA-E-treated rats and, conversely, a significant decrease in C20:4. In addition, EPA-E-treated rats showed a significant increase in GLUT4 mRNA in skeletal muscle when compared with control rats. Our results indicate that the beneficial effect of EPA-E on insulin resistance in OLETF rats is likely to be dependent on modification of the phospholipid components of the skeletal muscle membrane. These findings suggest that dietary fatty acids may play a key role in the development of insulin resistance in patients with NIDDM.

Alterations of insulin and glucagon secretion from the perfused pancreas before, at the onset and after the development of diabetes in male Otsuka Long-Evans Tokushima Fatty (OLETF) rats

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an obese non-insulin dependent diabetes mellitus (NIDDM) model of an inbred strain. In this study, basal (2.8 mM glucose) insulin and glucagon and their responses to glucose (16.7 mM) were examined at the age of 9 weeks (n = 3) before the onset of diabetes, at 23 weeks (n = 6) at the onset of diabetes, and at 48 weeks (n = 5) after the development of diabetes by pancreatic perfusion. In Long-Evans Tokushima Otsuka (LETO, control) rats, insulin responses to glucose showed a biphasic pattern at all three ages, while in OLETF rats, basal insulin concentrations were significantly increased compared to those in controls at the age of 9 and 48 weeks. Insulin responses to glucose showed no difference from controls at 9 and 23 weeks, however, at 48 weeks the response was significantly decreased. In controls, high basal glucagon concentrations showed significant decrease in response to glucose at all ages. In OLETF rats, basal glucagon concentrations showed significant decrease compared to those in control rats at 23 and 48 weeks. Glucagon response to glucose significantly decreased at 9 and 23 weeks, but at 48 weeks there was no change in concentration in response to glucose. Pancreatic insulin content was lower at 48 weeks in OLETF rats than in LETO rats, although no differences were observed at other ages. There were no significant differences in pancreatic glucagon content between the two groups at any age. Morphologically, in OLETF rats the number of pancreatic B cells were decreased and A cells migrated into the center of islets at 48 weeks. The results suggested that one of the causes of diabetes in OLETF rats is impaired insulin response to glucose.

Extrapancreatic action of truncated glucagon-like peptide-I in Otsuka Long-Evans Tokushima Fatty rats, an animal model for non-insulin-dependent diabetes mellitus

To clarify the mechanism(s) of the antidiabetic effects of truncated glucagon-like peptide-1 (GLP-1) in diabetics, we examined its insulinotropic and extrapancreatic effects in a newly established strain of spontaneously non-insulin-dependent diabetic (NIDDM) rats, Otsuka Long-Evans Tokushima Fatty (OLETF) rats, that received a continuous infusion of truncated GLP-1 620 pmol/d/kg (G group, n = 12) or of vehicle (V group, n = 12) for 4 weeks by Alzet pump. Nonfasting plasma glucose levels were significantly lower (P < .05) in the G group than in the V group (7.0 +/- 0.67 v 9.1 +/- 1.7 mmol/L), and fasting plasma immunoreactive insulin (IRI) levels were lower in the former than in the latter (0.63 +/- 0.31 v 0.78 +/- 0.25 nmol/L). At day 15 of infusion, the G group showed an attenuated plasma glucose response to an oral glucose load, but had plasma IRI levels comparable to those in the V group. A long-term infusion of truncated GLP-1 increased the glucose infusion rate (GIR) significantly (P < .05) during a euglycemic-hyperinsulinemic clamp test (59.0 +/- 14.8 mumol/kg/min for group G v 38.9 +/- 12.2 for group V), but hepatic glucose output (HGO) did not differ significantly for either group. Uptake of 2-deoxy-D-glucose (2DG) by peripheral muscles in the G group was as much as 2.4-fold higher than in the V group (5.52 +/- 2.04 v 2.29 +/- 0.97 mumol/100 g muscle weight/min). We conclude from these data that truncated GLP-1, in addition to its well-known incretin effect, is capable of augmenting insulin action in peripheral tissues of diabetics, which can contribute, in part, to improve glucose intolerance in OLETF rats.

Pancreatic A-cell function in the partially pancreatectomized Otsuka Long-Evans Tokushima Fatty rat, a model of spontaneous non-insulin-dependent diabetes mellitus

We examined whether a 70% pancreatectomy changes the morphofunctionality of pancreatic A cells in a model rat (Otsuka Long-Evans Tokushima Fatty [OLETF]) with non-insulin-dependent diabetes mellitus. Male OLETF rats aged 6 weeks were assigned to two groups: partial pancreatectomy (Px) and sham pancreatectomy (sham). The Px group was divided into three subgroups based on treatment received after surgery, which included treatment with nicotinamide, phlorhizin, or saline. As a control, their diabetes-resistant counterparts, Long-Evans Tokushima Otsuka (LETO) rats, were similarly treated and grouped. Six weeks after surgery, plasma glucagon responses to arginine- and insulin-induced hypoglycemia were examined. In addition, the glucagon content and morphological features of pancreatic A cells in Px-remnant and remnant-equivalent pancreata were investigated 7 weeks after surgery. A sustained nonfasting hyperglycemia was evident in Px OLETF rats, which was ameliorated by administration of nicotinamide. The glucagon content and A-cell mass were not decreased significantly in the remnant pancreas of saline- and phlorhizin-treated Px animals of either strain but increased in nicotinamide-treated animals compared with those in the remnant equivalent of the respective sham rats. The areas under the response curves of plasma glucagon (zigma IRG) during an arginine infusion test and 90 minutes of insulin-induced hypoglycemia were 1,010.7 +/- 72.9, 1,083.1 +/- 95.3, 1,029.6 +/- 65.0, and 1,779.8 +/- 226.9 pmol.L-1.min-1 versus 1,997.0 +/- 283.1,2,217.0 +/- 395.0, 1,479.6 +/- 78.0, and 3,466.4 +/- 174.0 pmol.L-1.min-1 in phlorhizin-, nicotinamide-, and saline-treated Px OLETF and sham OLETF rats, respectively. A similar trend was observed for differences in the response of pancreatic A cells to both stimuli among various groups of LETO rats. There was no significant difference in sigma IRGs during both tests between OLETF and LETO rats with similar treatments, except during an insulin tolerance test (ITT) in saline-treated Px rats. The magnitude of the plasma glucagon response to both stimuli in the test animals was roughly parallel to the glucagon content in the pancreas. These findings suggest that differences in the proliferation and responsiveness of pancreatic A cells between OLETF and LETO rats after a 70% pancreatectomy are not nearly as significant as compared with B cells.

Glucagon secretory response to hypoglycaemia, adrenaline and carbachol in streptozotocin-diabetic rats

Glucagon response to insulin-induced hypoglycaemia is impared in diabetes, but the mechanism is not established. Pancreatic A cell hyporesponsiveness to adrenergic or cholinergic stimulation could contribute to the impairment. We therefore compared the plasma glucagon responses to intravenous infusion of adrenaline (1200 ng kg(-1) min(-1) for 20 min) or to intravenous injection of the cholinergic agonist carbachol (50 micrograms kg(-1)) in chloral hydrate-anaesthetized rats made diabetic with the use of streptozotocin (80 mg kg(-1) subcutaneously) 6 weeks before and in anaesthetized control rats. Insulin was infused intravenously to reduce plasma glucose levels to below 1.8 mmol L(-1). As expected, the plasma glucagon response was reduced by approximately 45% in streptozotocin-diabetic rats compared with controls (P = 0.045). During adrenaline infusion, plasma glucagon levels increased by 277 +/- 92 pg mL(-1) in controls (P = 0.009) and by 570 +/- 137 pg mL(-1) in the diabetic rats (P = 0.002). Thus, the plasma glucagon response to adrenaline was approximately doubled in the diabetic rats (P = 0.045). Following carbachol injection, plasma glucagon levels were raised by 1211 +/- 208 pg mL(-1) (P < 0.001) in controls but only by 555 +/- 242 pg mL(-1) in the diabetic rats (P = 0.049). Thus, the plasma glucagon response to carbachol was impared by approximately 58% in the diabetic rats (P = 0.028). We conclude that carbachol-stimulated glucagon secretion is impared concomitantly with the impared glucagon response to hypoglycaemia in streptozotocin-diabetic rats, whereas adrenaline-induced glucagon secretion is exaggerated. We suggest that a reduced pancreatic A cell responsiveness to cholinergic stimulation could contribute to the impairment of the glucagon response to insulin-induced hypoglycaemia in diabetes.