Potentiation of arginine-induced glucagon secretion by adenosine

Adenosine and the synthetic adenosine agonists 2-chloroadenosine and N⁶-(L-2-phenylisopropyl)-adenosine were tested for effects on hormone secretion from the rat isolated perfused pancreas. These nucleosides, at concentrations of 5 μM, markedly potentiated both phases of arginine-induced glucagon release; the two synthetic agonists were more effective than adenosine. In the absence of arginine, each of the nucleosides induced a transient burst of glucagon. In contrast, adenosine and both synthetic agonists inhibited arginine-induced insulin secretion to varying degrees and caused only negligible insulin release when perfused without arginine. The adenosine antagonist 8-($\text{p}$-sulfophenyl)-theophylline prevented the actions of adenosine on hormone release from the pancreas. Our data suggest that adenosine potentiation of arginine-induced glucagon release may be mediated via adenosine receptors on alpha cell membranes; such a mechanism could provide an important endogenous control over glucagon secretion.     

The role of leucine-enkephalin on insulin and glucagon secretion from pancreatic tissue fragments of normal and diabetic rats

Leucine-enkephalin (Leu-Enk) has been shown to be present in endocrine cells of the rat pancreas and may play a role in the modulation of hormone secretion from the islets of Langerhans. Since little is known about the effect of Leu-Enk on insulin and glucagon secretion, it was the aim of this study to determine the role of Leu-Enk on insulin and glucagon secretion from the isolated pancreatic tissue fragments of normal and diabetic rats. Pancreatic tissue fragments of normal and streptozotocin-induced diabetic rats were incubated for 1 h with different concentrations of Leu-Enk (10(-12)-10(-6)M) alone or in combination with either atropine or yohimbine or naloxone. After the incubation period the supernatant was assayed for insulin and glucagon using radioimmunoassay techniques. Leu-Enk (10(-12 )-10(-6)M) evoked large and significant increases in insulin secretion from the pancreas of normal rats. This Leu-Enk-evoked insulin release was significantly (p < 0.05) blocked by atropine, naloxone and yohimbine (all at 10(-6)M). In the same way, Leu-Enk at concentrations of 10(-12)M and 10(-9)M induced significant (p < 0.05) increases in glucagon release from the pancreas of normal rats. Atropine, yohimbine but not naloxone significantly (p < 0.05) inhibited Leu-Enk-evoked glucagon release from normal rat pancreas. In contrast, Leu-Enk failed to significantly stimulate insulin and glucagon secretion from the pancreas of diabetic rats. In conclusion, Leu-Enk stimulates insulin and glucagon secretion from the pancreas of normal rat through the cholinergic, alpha-2 adrenergic and opioid receptor pathways.     

Development of hormonal peptides and processing enzymes in the embryonic avian pancreas with special reference to co-localisation

Studies on the developing mammalian pancreas have suggested that insulin and glucagon co-exist in a transient cell population and that peptide YY (PYY) marks the earliest developing endocrine cells. We have investigated this in the embryonic avian pancreas, which is characterised by anatomical separation of insulin and glucagon islets. Moreover, we have compared the development of the endocrine cells to that of processing enzymes involved in pancreatic hormone biosynthesis. PYY-like immunoreactivity occurred in islet cells from the youngest stages examined: it increased in amount from approximately 5 days of incubation and was co-localised with glucagon and to a lesser extent with insulin. Insulin and glucagon cells were numerous: co-existence of the two peptides in the same cells was but rarely observed. From the youngest stages examined, prohormone convertase (PC) 1/3-like immunoreactivity was detected in insulin cells and PC2-, 7B2- and carboxypeptidase E-like immunoreactivity in both glucagon and insulin cells. We conclude that: (1) PYY-like immunoreactivity occurs in avian islet cells but generally in lesser amounts than in mammals at the earlier stages, (2) the paucity of cells co-expressing insulin and glucagon indicate that all avian insulin cells do not pass through a stage where they co-express glucagon and (3) the early expression of the enzymes responsible for the processing of prohormones suggests that this process is initiated soon after islet cells first differentiate.     

Stimulation by prostaglandin E2 of glucagon and insulin release from isolated rat pancreas

To ascertain whether prostaglandins (PG) may play a role in the secretion of glucagon and in an attempt to elucidate the conflicting observations on the effects of PG on insulin release, the isolated intact rat pancreas was perfused with solutions containing 1.1 × 10⁻⁹ to 1.8 × 10⁻⁵M PGE₂. In the presence of 5.6 mM glucose significant increments in portal venous effluent levels of glucagon and insulin were observed in response to minimal concentrations of 2.8 × 10⁻⁸ and 1.4 × 10⁻⁷M PGE₂, respectively; a dose-response relationship was evident for both hormones at higher concentrations of PGE₂. When administered over 60 seconds, 1.4 × 10⁻⁶M PGE₂ resulted in a significant increase in glucagon levels within 24 seconds and in insulin within 48 seconds. Ten-minute perfusions of 1.4 × 10⁻⁶M PGE₂ elicited biphasic release of both islet hormones; Phase I glucagon release preceded that of insulin. Both phases of the biphasic glucagon and insulin release which occurred in response to 15-minute perfusions of 10 mM arginine were augmented by PGE₂. These observations indicate that PGE₂ can evoke glucagon and insulin release at concentrations close to those observed by others in the extracts of rat pancreas. We conclude that PG may be involved in the regulation of secretion of glucagon and insulin and may mediate and/or modify the pancreatic islet hormone response to other secretagogues.     

Diazepam: in vitro effects on glucagon and insulin release

Diazepam suppressed arginine-induced glucagon release from the isolated perfused rat pancreas in a dose-dependent manner, with an IC50 of approximately 65 microM. In contrast, insulin release was enhanced by 10-50 microM diazepam, but inhibited by higher concentrations of drug. Thus, 50 microM diazepam simultaneously suppressed glucagon and increased insulin release in this model. The potentiation of insulin release may result from phosphodiesterase inhibition. The inhibitory effects on hormone release are discussed in terms of diazepam's molecular conformation, which is similar to that of diphenylhydantoin, an inhibitor of both glucagon and insulin release in the isolated perfused rat pancreas. The possibility is also considered that the conformation of both compounds might be similar to the apparent active site of the hormone release inhibitor somatostatin.     

Comparison of insulin and glucagon pulsatile secretion between the rat and dog pancreas in-vitro

Sustained pulses of insulin and glucagon were obtained from the isolated perfused in vitro rat pancreas. The respective periodicity of hormone release (peak to peak interval) was calculated by the Pulsar computer algorithm as insulin 5.8 +/- 0.3 min and glucagon 6.5 +/- 0.25 min. Because pulsatile insulin secretion is absent in type II diabetics, pulsatile islet hormone secretion could theoretically be regulated directly by intra-islet hormone interactions or indirectly by hormone sensitive nerve feedback, possibly from a venous hormone sensitive receptor system within the pancreas. To test the possible contributions of these systems in pulse regulation, the direction of perfusion was reversed in both rat and dog pancreata to prevent hormone contact with putative venous hormone receptors. The periodicity of hormone secretion was unchanged by reversed perfusion in both species. As vascular perfusion of islet cells is normally B to A to D, these results suggest that neither intra-islet hormone interactions nor intra-pancreatic insulin or glucagon sensitive nerve feedback systems are responsible, on an acute basis, for the regulation of pulsatile insular secretion from the normal pancreas. Insulin regulates net glucagon secretion but does not acutely influence glucagon pulses. The presence of pulses during retrograde perfusion may be the result of the entrainment of the pacemaker-islet system. These observations are consistent with the presence of an independent pacemaker and neural coordinating system within the dog and rat pancreas which may influence both the A- and B-cell.     

Alloxan reversibly impairs glucagon release and glucose oxidation by pancreatic A2-cells

Alloxan is known as a selective B-cell cytotoxic substance, and there is so far little evidence for a direct toxic effect on the other islet cell types. To elucidate further whether such effects occur, the actions of alloxan on glucagon release and glucose oxidation were studied in isolated normal or A₂-cell-rich pancreatic islets of the guinea pig. The A₂-cell-rich islets were obtained from animals injected with streptozotocin 1–2 weeks before islet isolation. After exposure to alloxan (2 or 5mm) in vitro for 30min at 4°C, the islets were incubated in media containing either 1.7mm-glucose or 16.7mm-glucose plus 30m-i.u. of bovine insulin/ml. In both types of islet, alloxan abolished the ability of glucose and insulin both to decrease glucagon release and to increase the rate of glucose oxidation. A high concentration of glucose (28mm) during exposure to alloxan protected against these injurious effects. Tissue culture of alloxan-treated islets for 24h in 5.5mm-glucose restored neither the suppressive effect of glucose on glucagon release nor the inhibition of glucose oxidation of the A₂-cells. However, culture for 1 week completely normalized both the glucagon-secretory response and glucose oxidation by both kinds of islets. It is therefore concluded that alloxan affects the secretory mechanism of not only the B-cell but also of the islet A₂-cell, although this latter cell type is not primarily destroyed by the drug. The data furthermore support the concept of a relationship between glucose metabolism and the glucose-mediated glucagon release of the A₂-cell.     

Stimulation by prostaglandin E2 of glucagon and insulin release from isolated rat pancreas

To ascertain whether prostaglandins (PG) may play a role in the secretion of glucagon and in an attempt to elucidate the conflicting observations on the effects of PG on insulin release, the isolated intact rat pancreas was perfused with solutions containing 1.1 × 10⁻⁹ to 1.8 × 10⁻⁵M PGE₂. In the presence of 5.6 mM glucose significant increments in portal venous effluent levels of glucagon and insulin were observed in response to minimal concentrations of 2.8 × 10⁻⁸ and 1.4 × 10⁻⁷M PGE₂, respectively; a dose-response relationship was evident for both hormones at higher concentrations of PGE₂. When administered over 60 seconds, 1.4^−10−6M PGE₂ resulted in a significant increase in glucagon levels within 24 seconds and in insulin within 48 seconds. Ten-minute perfusions of 1.4 × 10⁻⁶M PGE₂ elicited biphasic release of both islet hormones; Phase I glucagon release preceded that of insulin. Both phases of the biphasic glucagon and insulin release which occurred in response to 15-minute perfusions of 10 mM arginine were augmented by PGE₂. These observations indicate that PGE₂ can evoke glucagon and insulin release at concentrations close to those observed by others in the extracts of rat pancreas. We conclude that PG may be involved in the regulation of secretion of glucagon and insulin and may mediate and/or modify the pancreatic islet hormone response to other secretagogues.     

Neuro-endocrine basis for altered plasma glucose homeostasis in the Fragile X mouse

Background

The fragile X mouse model shows an increase in seizure susceptibility, indicating an involvement of the GABAergic system via an alteration in cellular excitability. In the brain, we have previously described a reduction in GABA_A receptor expression as a likely basis for this susceptibility. In the brains of fragile X mice, this reduction in receptor expression culminates with a concomitant increase in the expression of glutamic acid decarboxylase (GAD), the enzyme responsible for GABA synthesis. Further, voltage-sensitive calcium channel expression is reduced in the pancreas of the fragile X mouse. Since there are considerable similarities in the GABAergic system in the brain and pancreas, we evaluated the protective role of taurine in pancreatic islet development in both wild type (WT) and fragile X mice (KO).

Methods

One-month-old FVB/NJ males or age-matched fmr1-knockout (KO) mice were supplemented with taurine in drinking water (0.05% w/v) for four weeks. Age-matched controls were fed water only for the same duration. At four weeks, mice were sacrificed and pancreases processed for histology and immunohistochemical studies on changes of insulin, glucagon and somatostatin expression. Additional mice were subjected to a glucose tolerance test.

Results

Taurine treatment resulted in a significant increase in the number and size of islets. WT taurine-fed mice, slightly hypoglycemic prior to glucose injection, showed significantly reduced plasma glucose at 30 min post-injection when compared to control mice. KO mice had normal baseline plasma glucose concentration; however, following glucose injection they had higher plasma glucose levels at 30 min when compared to controls. Supplementation of taurine to KO mice resulted in reduced baseline levels of plasma glucose. After glucose injection, the taurine-fed KO mice had reduced plasma glucose at 30 min compared to KO. Concomitant with the increased islets size and glucose tolerance observed in taurine-fed mice there was an increase in insulin, glucagon and somatostatin immunoreactivity in the islets of WT mice. In the KO mice however, insulin levels were not affected whereas glucagon and somatostatin levels were reduced. Exocytosis of these hormones is calcium-dependent, therefore any exacerbation of calcium homeostasis could affect hormone release. We found the expression of the voltage sensitive calcium channels (VSCC) is drastically reduced in the pancreas of fragile X mice.

Conclusions

During early development, the VSCC play an important role in calcium-dependent gene expression. Since these channels are also involved in depolarization and calcium-mediated vesicular release of neurotransmitters and pancreatic hormones, alterations in the expression of VSCC not only will affect calcium-mediated gene expression but also hormonal and neurotransmitter release creating therefore a neuroendocrine perturbation in the fragile X that may potentially affect other organ systems. We find that in the fragile X mouse, taurine treatment may partially restore functionality of the neuro-endocrine pancreas.

     

The endocrine pancreas of Alligator mississippiensis

Summary Immunocytochemical methods for light and electron microscopy were used to demonstrate the regulatory peptides present in the endocrine pancreas of thealligator, Alligator mississippiensis.The peptides studied included insulin, glucagon (pancreatic and enteric), somatostatin, pancreatic polypeptide (avian, bovine and human), vasoactive intestinal polypeptide, substance P, metenkephalin, -endorphin, C-terminal gastrin/CCK and gastric inhibitory polypeptide. Endocrine cells were detected using antisera to insulin, pancreatic glucagon, somatostatin and avian pancreatic polypeptide, whereas peptidergic nerves were stained with antisera to vasoactive intestinal polypeptide. All other antisera were unreactive in the alligator pancreas. The peptide-containing structures were identified ultrastructurally by both the semithin/thin and immuno-gold methods. The results showed that five of the regulatory peptides commonly detected in the mammalian pancreas were immunologically recognisable in the alligator. In addition, the ultrastructural appearance of the peptide-containing cells was clearly distinct from that reported in mammals.     

The Nitric Oxide Synthase Inhibitor NG-nitro-L-Arginine Methyl Ester Potentiates Insulin Secretion Stimulated by Glucose and L-Arginine Independently of its Action on ATP-Sensitive K+ Channels

The nature of the action of the nitric oxide synthase (NOS) inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) on hormone release from isolated islets was investigated. We found that glucose-induced insulin release was potentiated by L-NAME in the absence or presence of diazoxide, a potent channel opener, as well as in the presence of diazoxide plus a depolarizing concentration of K⁺. At a low, physiological glucose concentration L-NAME did not influence insulin secretion induced by K⁺ but inhibited glucagon secretion. L-arginine-induced insulin release was potentiated by L-NAME. This potentiation was observed also in the presence of K⁺ plus diazoxide. Further, glucagon release induced by L-arginine as well as by L-arginine plus K⁺ and diazoxide was suppressed by L-NAME. The results strongly suggest that the L-NAME-induced potentiation of insulin secretion in response to glucose or L-arginine as well as the inhibitory effects on glucagon secretion are largely mediated by L-NAME directly suppressing islet NOS activity. Hence NO apparently affects insulin and glucagon secretion independently of membrane depolarization events.     

Involvement of JAK2 and Src kinase tyrosine phosphorylation in human growth hormone-stimulated increases in cytosolic free Ca2+ and insulin secretion

We previously reported that human growth hormone (hGH) increases cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i) and proliferation in pancreatic -cells (Sjöholm Å, Zhang Q, Welsh N, Hansson A, Larsson O, Tally M, and Berggren PO. J Biol Chem 275: 21033–21040, 2000) and that the hGH-induced rise in [Ca²⁺]_i involves Ca²⁺-induced Ca²⁺ release facilitated by tyrosine phosphorylation of ryanodine receptors (Zhang Q, Kohler M, Yang SN, Zhang F, Larsson O, and Berggren PO. Mol Endocrinol 18: 1658–1669, 2004). Here we investigated the tyrosine kinases that convey the hGH-induced rise in [Ca²⁺]_i and insulin release in BRIN-BD11 -cells. hGH caused tyrosine phosphorylation of Janus kinase (JAK)2 and c-Src, events inhibited by the JAK2 inhibitor AG490 or the Src kinase inhibitor PP2. Although hGH-stimulated rises in [Ca²⁺]_i and insulin secretion were completely abolished by AG490 and JAK2 inhibitor II, the inhibitors had no effect on insulin secretion stimulated by a high K⁺ concentration. Similarly, Src kinase inhibitor-1 and PP2, but not its inactive analog PP3, suppressed [Ca²⁺]_i elevation and completely abolished insulin secretion stimulated by hGH but did not affect responses to K⁺. Ovine prolactin increased [Ca²⁺]_i and insulin secretion to a similar extent as hGH, effects prevented by the JAK2 and Src kinase inhibitors. In contrast, bovine GH evoked a rise in [Ca²⁺]_i but did not stimulate insulin secretion. Neither JAK2 nor Src kinase inhibitors influenced the effect of bovine GH on [Ca²⁺]_i. Our study indicates that hGH stimulates rise in [Ca²⁺]_i and insulin secretion mainly through activation of the prolactin receptor and JAK2 and Src kinases in rat insulin-secreting cells. c-Src; growth hormone receptor; prolactin receptor; Ca²⁺-induced Ca²⁺ release     

Somatostatin-induced inhibition of insulin secretion from isolated islets of rat pancreas in presence of glucagon.

In order to study the oeffect of somatostatin on the endocrine pancreas directly, islets isolated from rat pancreas by collagenase were incubated for 2 hrs 1) at 50 and 200 mg/100 ml glucose in the absence and presence of somatostatin (1, 10 and 100 mg/ml) and2) at 200 mg/100 ml glucose together with glucagon (5 mug/ml), with or without somatostatin (100 ng/ml). Immunologically measurable insulin was determined in the incubation media at 0, 1 and 2 hrs. Insulin release was not statistically affected by any concentration stomatostatin. On the other hand, somatostatin exerted a significant inhibitory action on glucagon-potentiated insulin secretion (mean +/- SEM, mu1/2 hrs/10 islets: glucose and glucagon: 1253 +/- 92; glucose, glucagon and somatostatin: 786 +/- 76). The insulin output in th epresence of glucose, glucagon and somatostatin was also significantly smaller than in thepresence of glucose alone (1104 +/- 126) or of glucose and somatostatin (1061 +/- 122). The failure of somatostatin to affect glucose-stimulated release of insulin from isolated islets contrasts its inhibitory action on insulin secretion as observed in the isolated perfused pancreas and in vivo. This discrepancy might be ascribed to the isolation procedure using collagenase. However, somatostatin inhibited glucagon-potentiated insulin secretion in isolated islets which resulted in even lower insulin levels than obtained in the parallel experiments without glucagon. It is concluded that the hormone of the alpha cells, or the cyclic AMP system, might play a part in the machanism of somatostatin-induced inhibition of insulin release from the beta-cell.     

Catecholamine-induced hyperglycemia in dogs: independence from alterations in pancreatic hormone release

Although isoproterenol is a very effective hyperglycemic agent in dogs, other species such as rats, baboons and man are resistant to this effect. In each of these species catecholamines exert pronounced effects on insulin and glucagon release from the pancreas. In man, baboons, and rats catecholamine-induced alterations in pancreatic hormone release indirectly influence the hyperglycemic response to these amines: glucagon release supports and insulin release limits hyperglycemic responses. In contrast, the present study demonstrates that in dogs catecholamine-induced hyperglycemic responses are relatively independent of concurrent alterations in pancreatic hormone release. In dogs isoproterenol produces hyperglycemia equal to or greater than responses to epinephrine despite large increases in insulin release produced by isoproterenol. Moreover, catecholamine-induced hyperglycemia is not significantly altered when insulin and glucagon release are blocked with somatostatin.     

The ontogeny of insulin secretion mechanisms

Insulin secretion from pieces of pancreas of rabbits aged 6 weeks or 1 day, or of 24-day foetuses was studied in vitro in response to glucose, glucagon and theophylline. Glucose did not stimulate insulin release from foetal pancreas but was effective postnatally. Glucagon in medium containing 3.0 mg glucose/ml stimulated insulin secretion equally at each stage of development. Theophylline in medium containing 0.6 or 3.0 mg glucose/ml stimulated insulin secretion from foetal pancreas but was effective on postnatal pancreas only in the presence of 3.0 mg glucose/ml. Glucose potentiated the action of theophylline on the foetal β cell and theophylline potentiated the action of glucose on the adult β cell.     

Involvement of the autonomic nervous system in the in vivo TRH-induced increases in the plasma levels of glucagon, insulin and glucose in rabbits

Thyrotropin-releasing hormone, TRH, increases the plasma levels of glucagon, insulin, glucose and free fatty acids in rabbits. However, TRH has no direct effects on the release of hormones neither from the endocrine pancreas in humans nor from the isolated perfused rat pancreas. The aim of the present study was to investigate if the effects of TRH in rabbits were mediated by the autonomic nervous system. The TRH "Roche"-induced hyperglucagonemia was inhibited by phentolamine (an alpha-receptor blocking drug), yohimbine (an alpha-2 -receptor blocking drug) and atropine. The TRH "Roche"-induced hyperinsulinemia was inhibited by propranolol (a beta-receptor blocking drug). The TRH "Roche"-induced hyperglycemia was inhibited by all four drugs. The TRH "Roche"-induced increases in the plasma levels of free fatty acids were not inhibited by the sympathetic and parasympathetic blocking drugs. The effects of TRH "Roche" on the plasma levels of glucagon, insulin and glucose cannot be explained by increases in the plasma levels of catecholamines. TRH, given intravenously into rabbits, may possibly act on regions in the central nervous system which control carbohydrate metabolism and the release of glucagon and insulin from the endocrine pancreas by sympathetic and parasympathetic mechanisms.     

Effects of pancreastatin on insulin, glucagon and somatostatin secretion by the perfused rat pancreas

Pancreastatin is a novel peptide, isolated from porcine pancreatic extracts, which has been shown to inhibit glucose-induced insulin release "in vitro". To achieve further insight into the influence of pancreastatin on pancreatic hormone secretion, we have studied the effects of this peptide on unstimulated insulin, glucagon and somatostatin output, as well as on the responses of these hormones to glucose and to tolbutamide in the perfused rat pancreas. Pancreastatin strongly inhibited unstimulated insulin release as well as the insulin responses to glucose and to tolbutamide. It did not significantly affect glucagon or somatostatin output under any of the above-mentioned conditions. These findings suggest that pancreastatin inhibits B-cell secretory activity directly, and not through an A-cell or D-cell paracrine effect.     

Stimulation by prostaglandin E2 of glucagon and insulin release from isolated rat pancreas.

To ascertain whether prostaglandins (PG) may play a role in the secretion of glucagon and in an attempt to elucidate the conflicting observations on the effects of PG on insulin release, the isolated intact rat pancreas was perfused with solutions containing 1.1 x 10(-9) to 1.8 x 10(-5)m PGE2. In the presence of 5.6 mM glucose significant increments in portal venous effluent levels of glucagon and insulin were observed in response to minimal concentrations of 2.8 X 10(-8) and 1.4 X 10(-7) PGE2, respectively; a dose-response relationship was evident for both hormones at higher concentrations of PGE2. When administered over 60 seconds, 1.4 X 10(-6)M PGE2 resulted in a significant increase in glucagon levels within 24 seconds and in insulin within 48 seconds. Ten-minute perfusions of 1.4 X 10(-6)M PGE2 elicited biphasic release of both islet hormones; Phase I glucagon release preceded that of insulin. Both phases of the biphasic glucagon and insulin release which occurred in response to 15-minute perfusions of 10 mM arginine were augmented by PGE2. These observations indicate that PGE2 can evoke glucagon and insulin release at concentrations close to those observed by others in the extracts of rat pancreas. We conclude that PG may be involved in the regulation of secretion of glucagon and insulin and may mediate and/or modify the pancreatic islet hormone response to other secretagogues.     

Immunocytochemical study of the distribuition of endocrine cells in the pancreas of the Brazilian sparrow species Zonotrichia Capensis Subtorquata (Swaison, 1837).

In the present study, we investigated types of pancreatic endocrine cells and its respective peptides in the Brazilian sparrow species using immunocytochemistry. The use of polyclonal specific antisera for somatostatin, glucagon, avian pancreatic polypeptide (APP), YY polypeptide (PYY) and insulin, revealed a diversified distribution in the pancreas. All these types of immunoreactive cells were observed in the pancreas with different amounts. Insulin-Immunoreactive cells to (B cells) were most numerous, preferably occupying the central place in the pancreatic islets. Somatostatin, PPA, PYY and glucagon immunoreactive cells occurred in a lower frequency in the periphery of pancreatic islets.     

Defective blood glucose counter-regulation in diabetics is a selective form of autonomic neuropathy.

Administration of a low-dose insulin infusion to normal subjects results in a mild drop in blood glucose concentration (1.1 mmol/1 (20 mg/100 ml)) and the resetting of the basal glucose at the lower concentration. Clinical hypoglycaemia does not develop, and there is a significant release of glucagon, growth hormone, and cortisol. A similar infusion in insulin-requiring diabetics results in hypoglycaemia accompanied by a release of growth hormone and cortisol but no significant release of glucagon. Subsequently giving arginine to these patients results in a significant release of glucagon, indicating that the alpha cell is intact and can respond to local, direct stimulation. In one patient the defect in glucagon response to impending hypoglycaemia developed after two years'' insulin treatment. This type of dissociated response'' of the alpha cell has been reported in animals after denervation of the pancreas, and insulin-requiring diabetics may develop a selective form of autonomic neuropathy affecting the vagal control of glucagon release.