Insulin and glucagon release in the diabetic Chinese hamster: Differences among inbred sublines

Summary Release of insulin and glucagon from perfused pancreases in vitro of 40 normal male and female Chinese hamsters (from one inbred subline) and 110 male and female diabetic hamsters (from three inbred sublines) was measured in response to glucose plus arginine, theophylline alone, or potassium alone, in order to determine if differences in hormone secretion exist among different diabetic sublines. Glucose plus arginine and potassium produced subnormal insulin responses in all three diabetic sublines, whereas theophylline induced normal or above normal insulin responses. Excessive glucagon release was consistently seen in only one diabetic subline. The female normal animals showed greater insulin release than the male normal hamsters in response to glucose plus arginine. This sex difference was not seen in the diabetic animals.     

Stimulation of insulin and somatostatin release by two meglitinide analogs

Several meglitinide analogs are currently under investigation as potential insulinotropic tools for the treatment of noninsulin-dependent diabetes. The present study aimed to further insight into the effect of these agents on the secretion of insulin, glucagon, and somatostatin by the isolated perfused pancreas. Both repaglinide (0.01 μM) and A-4166 (1.0 μM) stimulated insulin and somatostatin release, but failed to affect glucagon output, from pancreases exposed to 5.6 mM d-glucose. The secretory response of the B- and D-cells to the hypoglycemic agents was much less marked than that caused by a rise in hexose concentration from 5.6–16.7 mM. Although repaglinide was tested at a concentration a hundred times lower than that of A-4166, the drug-induced increase in both insulin and somatostatin secretion persisted for a longer time after exposure to repaglinide, than to A-4166. The relevance of these findings to the use of meglitinide analogs as antidiabetic agents is double. First, they document that these drugs, although enhancing both insulin and somatostatin release, do not provoke an undesirable stimulation of glucagon secretion. Second, they indicate that even at a very low concentration, repaglinide provokes a protracted insulinotropic action, thus suggesting that the reversibility of the secretory response to this or other meglitinide analogs represents an intrinsic molecular attribute, unrelated to either their biological potency or the relative extent of B-cell stimulation.     

Somatotrophic diabetes: Insulin release responses to arginine and glucagon in dogs

Summary Growth hormone injected daily in 6 dogs for 6 days caused a 20-fold elevation in fasting serum immunoreactive insulin (IRI) without appreciable change in serum glucose in 1 day. In the somatotrophic diabetes that occurred after 2 days, the hyperinsulinaemia was maintained and the serum IRI/glucose (I/G) ratio declined from the early high level but remained elevated. During this treatment, in response to glucose infusion, the rise in serum IRI above the initially high fasting level was 16 times the normal. In response to glucagon, the rise in IRI was twice the normal and the rise in glucose was more prolonged, resulting in a decline in the I/G ratio. In response to arginine infusion, the rise in serum IRI was 8 times the normal and the rise in the I/G ratio was twice normal. Following a meal, the rise in serum IRI was 8 times the normal. Thus, with growth hormone treatment the insulin secretory responses to these stimulating factors were magnified over the already elevated fasting level of secretion. The insulin content of the pancreas was reduced to less than 10% of normal by growth hormone treatment for 6 days, due apparently to elevation of the rate of secretion over the rate of formation of insulin.     

Insulin and glucagon response of the diabetic Chinese hamster in the Asahikawa colony

The relationship between pancreatic hormone content and pattern of hormone release has not been completely elucidated because of heterogeneity in diabetes. Accordingly, this study was performed to establish the relationship, using spontaneously diabetic Chinese hamsters in the Asahikawa colony, a newly discovered experimental model resembling insulin-deficient diabetes in humans. As a result of investigations of insulin and glucagon responses to glucose or arginine in vivo and in vitro using isolated islets obtained by the collagenase procedure, a decreased insulin response and paradoxical glucagon response to glucose, and an excessive glucagon response to arginine were found in the diabetic animals. While the yield of isolated islets tended to decrease, a decreased pancreatic insulin content and increased pancreatic glucagon content were found as the diabetic state advanced. It may be suggested, therefore, that the relationship between pancreatic hormone content and pattern of hormone release in diabetic animals in the Asahikawa colony is based on the disruption of islets, disruption or dysfunction of B-cells and hyperplasia or hypertrophy of A-cells by some cause genetically determined.     

Does glucagon play a role in the insulin resistance of patients with adult non-ketotic diabetes?

Summary Using a constant intravenous infusion technique we have measured in vivo insulin resistance in 17 normal subjects, five patients with chemical diabetes, and 13 non-ketotic diabetic patients with fasting hyperglycaemia (FBS>120 mg/ 100 ml). All of the diabetic patients were non-obese. The results demonstrated that the diabetic patients were insulin resistant compared to normals and that the degree of insulin resistance was greater the more severe the diabetes. No differences in plasma glucagon levels were found among the different groups during the infusion studies. These results demonstrate that non-obese, non-ketotic diabetic patients are insulin resistant and that abnormalities in plasma glucagon concentrations do not account for this insulin resistance.Dr. Olefsky is a Clinical Investigator with the Veterans AdministrationDr. Sperling is a recipient of a Research Career Development Award from the U. S. P. H. S., 1K04-HD 00029Dr. Reaven is a Medical Investigator with the Veterans Administration     

Streptozotocin-induced diabetes in the Chinese hamster

Summary Streptozotocin treatment (125 mg/kg) in the Chinese hamster induced hyperglycaemia, hypoinsulinaemia, hyperglucagonaemia and changes in body, liver, pancreas, stomach, kidney and adipose tissue weights. The pancreatic reserves of insulin and glucagon in the diabetic animals were low, but stomach glucagon high. These animals showed high levels of phosphoenolpyruvate carboxykinase and low levels of glucokinase, hexokinase, isocitrate dehydrogenase and malic enzyme, but normal levels of pyruvate kinase in the liver. Increases in lactate dehydrogenase subunit B and isozymes 2, 3 and 4 were also observed in the liver, but not in the epididymal fat pad, of the diabetic animals. N-Acetyl--D-glucosaminidase was elevated in plasma, liver and heart, but not in the kidney of the treated animals. Renal -galactosidase and – glucosidase were depressed, whereas -galactosidase and -glucosidase remained essentially normal. These features indicated that there were considerable differences between the biochemical disorders associated with streptozotocin-diabetes in the Chinese hamster and the published observations in the rat.     

Effect of a long acting glucagon selective somatostatin analogue on plasma glucose,insulin and glucagon levels in the anaesthetized rat during arginine infusion

Summary The effects of somatostatin and a long acting, glucagon selective somatostatin analog (des-Ala¹Gly²[His^4,5-D-Trp⁸]-somatostatin), were studied during arginine tolerance tests in normal anaesthetized rats. Arginine infusion in control animals resulted in a rapid increase in plasma insulin and glucagon, and an increase of 15±5 mg/dl in plasma glucose. Somatostatin infusion (1 mg/kg/h) resulted in suppression of basal insulin secretion and a decrease in arginine-induced insulin and glucagon release. Glucose levels increased rapidly during the combined arginine-somatostatin infusion reaching a peak of 72±10 mg/dl above basal levels. Similar results were obtained when somatostatin was injected SC (1 mg/kg) at times 0, 15, 30, and 45 minutes (arginine infused from 30–60 minutes). A single injection (1 mg/kg) of the long-acting somatostatin analogue resulted in significant inhibition of basal insulin and glucagon release; during arginine infusion glucagon levels rose only slightly, the insulin response was, however, nearly normal, and only a small arginine-induced increase in glucose levels was observed. Carbohydrate absorption was not influenced by either somatostatin or the analogue.     

Difference in calcium dependency of insulin,glucagon and somatostatin secretion in response to glibenclamide in perfused rat pancreas

Summary The extracellular calcium requirements for insulin, glucagon and somatostatin release induced by 1 g/ml of glibenclamide have been compared in the perfused, isolated rat pancreas. In the absence of glucose, the drug evoked insulin release equally well at physiological (2.6 mmol/l) and low (0.25 mmol/l) levels of total calcium. In contrast, glibenclamide evoked somatostatin release at 2.6 but not at 0.25 mmol/l of calcium. At 2.6 mmol/l of calcium, glibenclamide evoked bimodal effects (stimulation followed by inhibition) on glucagon secretion. At 0.25 mmol/l of calcium, basal secretory rates of glucagon were elevated and a small stimulatory effect of glibenclamide was seen. Addition of 0.5 mmol/l of EGTA to media with low calcium concentrations uniformly abolished the A, B and D cell secretory responses to glibenclamide. The possible modulation of calcium dependency by a non-stimulatory concentration of glucose was tested by its addition at 3.3 mmol/l to the perfusion media. Glucose enhanced glibenclamide-induced insulin secretion, both at 0.25 and 2.6 mmol/l of calcium. However, at 0.25 mmol/l of calcium, the enhancing effect of glucose was more pronounced than at 2.6 mmol/l. At 2.6 mmol/l of calcium, glucose diminished the somatostatin and abolished the glucagon response to glibenclamide. At 0.25 mmol/l of calcium, glucose did not influence somatostatin release while the presence of the sugar diminished basal and glibenclamide-induced glucagon secretion. The present data confirm the requirement of extracellular calcium for A, B and D cell secretion, demonstrating different calcium dependencies for the cell types and indicate that this dependency can, in part, be modulated by glucose.     

Characterisation of somatostatin release from the pancreas

Summary The effect of calcium on somatostatin secretion was investigated in the isolated, perfused canine pancreas preparation and compared with those of acetylcholine, glucose, isoproterenol and arginine. Calcium (5 mmol/l) stimulated somatostatin release in a typical biphasic response pattern being about 5 times as potent as acetylcholine (1 mol/l), arginine (5 mmol/l), and isoproterenol (2 ng/ml) while the release of insulin and glucagon in response to calcium and the other secretagogues were of the same magnitude. Somatostatin release increased progressively when perfusate calcium was increased step-wise from 0 through 1.25 and 2.5 to 5.0 mmol/l. Calcium stimulated the secretion of somatostatin in the absence of glucose. The stimulatory effect of calcium was, however, modulated by the glucose concentration being about twice as large at 200 mg/100 ml as at 25 mg/100 ml glucose in the perfusion medium.     

Neurotransmitters partially restore glucose sensitivity of insulin and glucagon secretion from perfused streptozotocin-induced diabetic rat pancreas

Summary To elucidate the mechanisms of insensitivity of hormone secretion to glucose in streptozotocin-induced diabetic rat islets, we investigated the effects of acetylcholine (ACh) and norepinephrine on insulin and glucagon secretion in response to changes in glucose concentration, using perfused pancreas preparations. Basal insulin secretion at a blood glucose level of 5.6 mmol/l was significantly higher and basal glucagon secretion significantly lower in streptozotocin-induced diabetic rats than in controls, and neither high (16.7 mmol/l) nor low (1.4 mmol/l) blood glucose concentrations influenced insulin or glucagon secretion. Addition of 10^–6 mol/l ACh to the perfusate increased glucose-stimulated insulin secretion. Also, 10^–6 mol/l ACh, 10^–7 mol/l norepinephrine, as well as a combination of both, induced marked glucagon secretion, this was suppressed by high blood glucose level. Although simultaneous addition of 10^–6 mol/l ACh and 10^–7 mol/l norepinephrine induced only a slight increase in glucagon secretion in response to glucopenia, there was a significant increase in glucagon secretion in conjunction with an ambient decrease in insulin. Histopathological examination revealed a marked decline in acetylcholinesterase and monoamine-oxidase activities in the islets of streptozotocin-induced diabetic rats. We speculate that reduction of the potentiating effects of ACh and norepinephrine lessens glucose sensitivity of islet beta and alpha cells in this rat model of diabetes.Abbreviations STZ Streptozotocin - STZD streptozotocin-induce diabetic - ACh acetylcholine - AChE acetylcholinesterase - NE norepinephrine - MAO monoamine-oxidase     

Insulin secretion in vitro by the pancreas of the Chinese Hamster

Summary Insulin secretion by pancreatic tissuein vitro in response to glucose was related to plasma glucose and plasma insulin levels during life, and to the degree of granulation of the islets of Langerhans in 22 normal, 6 diabetic and 8 intermittently glycosuric Chinese Hamsters. Secretion was directly related to the insulin content of the pancreas and to the ratio of insulin to glucose in plasma, irrespective of the metabolic state of the animal, but was lowest in diabetic animals and highest in those with intermittent glycosuria. The relevance of these findings to current theories concerning prediabetes is discussed.

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Insulinsekretion des Pankreas chinesischer Hamster in vitro

Zusammenfassung Die durch Glucose stimulierte Insulinsekretion wurdein vitro am Pankreasgewebe chinesischer Hamster gemessen und mit den Glucose- und Insulin-Plasmaspiegeln derselben Tierein vivo, sowie mit der Granulierung derer Inselzellen (22 normale, 6 diabetische und 8 zeitweise glykosurischer chinesischer Hamster) verglichen. Es bestand eine direkte Korrelation zwischen Insulinsekretion und Insulingehalt des Pankreas, sowie mit dem Verhältnis Insulin/Glucose im Plasma, ohne Rücksicht auf den Stoffwechsel-Zustand der Tiere. Die niedrigsten Werte wurden allerdings bei den diabetischen Tieren, und die höchstens bei denjenigen mit zeitweiser Glykosurie beobachtet. Die Bedeutung dieser Resultate in bezug auf bestehende Theorien des Pre Diabetes wird diskutiert.

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Sécrétion d'insuline in vitro par le pancréas du hamster chinois

Résumé Nous avons mesuré la sécrétion d'insuline du tissu pancréatiquein vitro en présence de glucose chez 22 hamsters chinois normaux, 6 diabétiques et 8 ayant montré une glucosurie intermittente. Les valeurs obtenues ont été comparées avec l'hyperglycémie et l'insulinémie de ces mêmes animaux avant leur mort. Nous avons observé que la sécrétion insuliniquein vitro était proportionnelle au contenu en insuline du pancréas et au quotient de l'insulinémie divisée par le glucose plasmatique indépendamment de l'état métabolique de l'animal. Pourtant, la sécrétion insuliniquein vitro la plus basse a été observée chez les animaux diabétiques, et la plus élevée chez ceux qui avaient présenté une glucosurie intermittente. La relation possible de ces observations avec les théories actuelles du »pré-diabète« est discutée.

     

Insulin,glucagon and somatostatin secretion by cultured islets from normal and diabetic hamsters

Summary The interhormonal relationship within the pancreatic islets have been studied by previous investigators, but the cellular interplay and the sequence of events in the islet cell's response to stimulators has remained unclear. In the present study, pancreatic islets were isolated by collagenase digestion from normal and streptozotocin-diabetic hamsters the latter being maintained with insulin treatment. The diabetic animals were used to provide A- and B-cell enriched islets. The islets from normal and diabetic hamsters were cultured in medium 199 plus 10% fetal calf serum with 0.8 or 5 mg/ml glucose. The cultures were maintained for up to seven days     

The serum glucose response to glucagon suppression with somatostatin,insulin or antiglucagon serum in depancreatized rats

Summary Total immunoreactive glucagon (IRG) and immunoreactive glucagon of A cell origin (IRG_a) were measured in the serum of normal, sham-operated and depancreatized rats, after the administration of three glucagon antagonists: insulin (5–200 mU/rat/h), somatostatin (SRIF; 100 g/kg/h) and antiglucagon serum (AGS, enough to bind three times the calculated total amount of circulating IRG). Since no differences were noted between the responses of normal and sham-operated animals, the values were pooled and used as controls. Pancreatectomy caused a significant increase in serum glucose, IRG_a and total IRG and a significant decrease in serum insulin. AGS and SRIF significantly decreased serum glucose in control, but not in depancreatized rats, even though SRIF caused a significant decrease of IRG_a in all animals. SRIF significantly decreased plasma insulin in control rats, but did not modify total IRG secretion in either group. In control rats the minimum effective hypoglycaemic dose of insulin (5 mU/rat/h) may have decreased serum IRG_a, but not total IRG. At higher doses (20 mU/rat/h) insulin stimulated glucagon secretion. In depancreatized animals, higher doses of insulin (200 mU/rat/h) were needed to lower serum glucose. On the other hand, a dose of 100 U/rat/h was sufficient to lower the serum IRG. We conclude that although hyperglucagonaemia may contribute to the hyperglycaemia of the untreated depancreatized rats, the excessive secretion of glucagon is secondary to insulin insufficiency and that, at least in this animal model, the hypoglycaemic action of insulin is only minimally dependent upon its ability to suppress glucagon secretion.     

Insulin and glucagon secretion in diabetic and non-diabetic patients with circulating islet cell antibodies

Summary Thirty-nine patients (14 non-diabetics, 8 chemical diabetics, and 17 overt diabetics) with circulating islet cell antibodies (ICA) were studied. Insulin and glucagon secretion after oral (100 g) and intravenous glucose loading (200 mg/kg bolus injection followed by an infusion of 20 mg/min over 60 min) and arginine infusion (25 g over 30 minutes) were evaluated in these patients and in non diabetic and diabetic ICA-negative controls. In the non-diabetic groups with or without ICA, insulin and glucagon responses to glucose were similar. Moreover, in ICA positive patients the response of these hormones to arginine infusion was reduced. Similar alterations in insulin and glucagon secretion were observed in the ICA positive and negative patients with chemical or overt diabetes. In particular, fasting hyperglucagonaemia and glucagon hyperresponse to arginine are associated with a lack of insulin secretion in the patients with overt diabetes. Hormonal differences between diabetics with and without ICA could not be detected.This work was previously presented at the 12th Meeting of the European Association for the Study of Diabetes, Helsinki, September 1976 and published in abstract form in Diabetologia12, 422 (1976)     

Immediate and delayed effects of D-fructose upon insulin, somatostatin, and glucagon release by the perfused rat pancreas

Novel information was recently provided concerning the reciprocal effects of d-glucose and d-fructose upon their respective metabolism in rat pancreatic islets. In the light of such findings, this study aims at comparing the effects of d-glucose and d-fructose on insulin, somatostatin, and glucagon release from the isolated perfused rat pancreas. A rise in d-glucose concentration from 3.3 to 5.0 or 7.3 mM or the administration of d-fructose (17 and 40 mM) in the presence of 3.3 mM d-glucose stimulated insulin release in a concentration-related manner, but failed to affect somatostatin output. The secretion of glucagon was decreased in all cases. The secretory response to l-arginine (5 mM), 25 min after restoring the basal concentration of d-glucose, was more markedly affected, in terms of potentiation of insulin and somatostatin release and reduction of glucagon output, after prior administration of d-fructose than after a prior increase in d-glucose concentration. These findings argue against any major role for a paracrine regulation of hormonal release and, instead, are consistent with a causal link between metabolic and secretory events in the islet cells. Nevertheless, the present results emphasize differences in the response of distinct pancreatic endocrine cell types to the same or distinct hexoses.     

Effects of somatostatin receptor type 2 antagonism during insulin-induced hypoglycaemia in male rats with prediabetes

Aims

To examine if glucagon counterregulatory defects exist in a rat model of prediabetes (pre-T2D) and to assess if a selective somatostatin receptor 2 antagonist (SSTR2a), ZT-01, enhances the glucagon response to insulin-induced hypoglycaemia.

Materials and methods

Hyperglycaemia was induced in 8- to 9-week-old male, Sprague-Dawley rats via 7 weeks of high-fat diet followed by a single, low-dose intraperitoneal injection of streptozotocin (30 mg/kg). After 2 weeks of basal insulin therapy (0-4 U/d insulin glargine, administered subcutaneously [SC]) to facilitate partial glycaemic recovery and a pre-T2D phenotype, n = 17 pre-T2D and n = 10 normal chow-fed control rats underwent the first of two hypoglycaemic treatment-crossover experiments, separated by a 1-week washout period. On each experimental day, SSTR2a (3 mg/kg ZT-01, SC) or vehicle was administered 1 hour prior to insulin-induced hypoglycaemia (insulin aspart, 6 U/kg, SC).

Results

Glucagon counterregulation was marginally reduced with the induction of pre-T2D. Treatment with SSTR2a raised peak plasma glucagon levels and glucagon area under the curve before and after insulin overdose in both and pre-T2D rats. Blood glucose concentration was elevated by 30 minutes after SSTR2a treatment in pre-T2D rats, and hypoglycaemia onset (≤3.9 mmol/L) was delayed by 15 ± 12 minutes compared with vehicle (P < 0.001), despite similar glucose nadirs in the two treatment groups (1.4 ± 0.3 mmol/L). SSTR2a treatment had no effect on blood glucose levels in the control group or on the hypoglycaemia-induced decline in plasma C-peptide levels in either group.

Conclusions

Treatment with an SSTR2a increases glucagon responsiveness and delays the onset of insulin-induced hypoglycaemia in this rat model of pre-T2D where only a modest deficiency in glucagon counterregulation exists.     

Insulin resistance and mechanical dysfunction in hearts of Wistar rats with streptozotocin-induced non-insulin-dependent diabetes mellitus

Summary The present study correlates the insulin resistance seen in the myocardium of rats with streptozotocin-induced non-insulin-dependent diabetes mellitus with insulin secretory defects, hyperglycaemia and disease duration. Two-day-old male Wistar rats were given a bolus injection of streptozotocin (0.09 mg/g body weight) which caused glucose intolerance when these animals reached adulthood. Although these rats developed a progressive resistance to the actions of insulin in the heart this did not correlate with the development of glucose intolerance. However, a correlation was seen with a shift in insulin secretory response from hyper- to hypo-secretion which developed between 6 and 14 months of age. Moreover, this shift in secretory pattern can be associated with the onset of a cardiac mechanical malfunction.