Glucagon and diabetes: a reappraisal

The relationship between glucose and the liver-alpha cell axis - A systematic review

Until recently, glucagon was considered a mere antagonist to insulin, protecting the body from hypoglycemia. This notion changed with the discovery of the liver-alpha cell axis (LACA) as a feedback loop. The LACA describes how glucagon secretion and pancreatic alpha cell proliferation are stimulated by circulating amino acids. Glucagon in turn leads to an upregulation of amino acid metabolism and ureagenesis in the liver. Several increasingly common diseases (e.g., non-alcoholic fatty liver disease, type 2 diabetes, obesity) disrupt this feedback loop. It is important for clinicians and researchers alike to understand the liver-alpha cell axis and the metabolic sequelae of these diseases. While most of previous studies have focused on fasting concentrations of glucagon and amino acids, there is limited knowledge of their dynamics after glucose administration. The authors of this systematic review applied PRISMA guidelines and conducted PubMed searches to provide results of 8078 articles (screened and if relevant, studied in full). This systematic review aims to provide better insight into the LACA and its mediators (amino acids and glucagon), focusing on the relationship between glucose and the LACA in adult and pediatric subjects.

Glucagon revisited: Coordinated actions on the liver and kidney

Glucagon secretion is stimulated by a low plasma glucose concentration. By activating glycogenolysis and gluconeogenesis in the liver, glucagon contributes to maintain a normal glycemia. Glucagon secretion is also stimulated by the intake of proteins, and glucagon contributes to amino acid metabolism and nitrogen excretion. Amino acids are used for gluconeogenesis and ureagenesis, two metabolic pathways that are closely associated. Intriguingly, cyclic AMP, the second messenger of glucagon action in the liver, is released into the bloodstream becoming an extracellular messenger. These effects depend not only on glucagon itself but on the actual glucagon/insulin ratio because insulin counteracts glucagon action on the liver. This review revisits the role of glucagon in nitrogen metabolism and in disposal of nitrogen wastes. This role involves coordinated actions of glucagon on the liver and kidney. Glucagon influences the transport of fluid and solutes in the distal tubule and collecting duct, and extracellular cAMP influences proximal tubule reabsorption. These combined effects increase the fractional excretion of urea, sodium, potassium and phosphates. Moreover, the simultaneous actions of glucagon and extracellular cAMP are responsible, at least in part, for the protein-induced rise in glomerular filtration rate that contributes to a more efficient excretion of protein-derived end products.

The Role of Biomaterials in Insulin Delivery Systems

The control of blood glucose levels in diabetes involving devices are critically reviewed, and the role of blood-contacting biomaterial components analyzed. These include mechanical insulin-delivery systems of the closed-loop type that require an electronic glucose sensor and feedback, and open-loop systems that deliver insulin without a sensor and feedback. Whole pancreatic and islet transplantations, islet encapsulation, and the potential role of polymeric sustained drug delivery systems are discussed. The medical and social impacts of diabetes mellitus are of prime public health concern and of even greater magnitude than those of heart disease in the United States. While future advances in device design, miniaturization, and biometrials technology will significantly add to the arsenal of therapeutic alternatives, devices capable of controlling blood glucose levels ought to be viewed as mere interim phases rather than as final goals of the problem.

Investigational glucagon receptor antagonists in Phase I and II clinical trials for diabetes

INTRODUCTION

Despite type 2 diabetes (T2D) being recognized as a bihormonal pancreatic disease, current therapies are mainly focusing on insulin, while targeting glucagon has been long dismissed. However, glucagon receptor (GCGr) antagonists are currently investigated in clinical trials. Area covered: Following a brief description of the rationale for antagonizing GCGr in T2D, lessons from GCGr knock-out mice and pharmacological means to antagonize GCGr, a detailed description of the main results obtained with GCGr antagonists in Phase I-II clinical trials is provided. The development of several small molecules has been discontinued, while new ones are currently considered as well as innovative approaches such as monoclonal antibodies or antisense oligonucleotides inhibiting GCGr gene expression. Their potential benefits but also limitations are discussed. Expert opinion: The proof-of-concept that antagonizing GCGr improves glucose control in T2D has been confirmed in humans. Nevertheless, some adverse events led to stopping the development of some of these GCGr antagonists. New approaches seem to have a better benefit/risk balance, although none has progressed to Phase III clinical trials so far. Pharmacotherapy of T2D is becoming a highly competitive field so that GCGr antagonists should provide clear advantages over numerous existing glucose-lowering medications before eventually reaching clinical practice.

Regulation of hepatic glucose metabolism in health and disease

The liver is crucial for the maintenance of normal glucose homeostasis - it produces glucose during fasting and stores glucose postprandially. However, these hepatic processes are dysregulated in type 1 and type 2 diabetes mellitus, and this imbalance contributes to hyperglycaemia in the fasted and postprandial states. Net hepatic glucose production is the summation of glucose fluxes from gluconeogenesis, glycogenolysis, glycogen synthesis, glycolysis and other pathways. In this Review, we discuss the in vivo regulation of these hepatic glucose fluxes. In particular, we highlight the importance of indirect (extrahepatic) control of hepatic gluconeogenesis and direct (hepatic) control of hepatic glycogen metabolism. We also propose a mechanism for the progression of subclinical hepatic insulin resistance to overt fasting hyperglycaemia in type 2 diabetes mellitus. Insights into the control of hepatic gluconeogenesis by metformin and insulin and into the role of lipid-induced hepatic insulin resistance in modifying gluconeogenic and net hepatic glycogen synthetic flux are also discussed. Finally, we consider the therapeutic potential of strategies that target hepatosteatosis, hyperglucagonaemia and adipose lipolysis.

Inhibiting or antagonizing glucagon: making progress in diabetes care

Absolute or relative hyperglucagonaemia has been recognized for years in all experimental or clinical forms of diabetes. It has been suggested that excess secretion of glucagon by the islet α cells is a direct consequence of intra-islet insulin secretory defects. Recent studies have shown that knockout of the glucagon receptor or administration of a monoclonal specific glucagon receptor antibody make insulin-deficient type 1 diabetic rodents thrive without insulin. These observations suggest that glucagon plays an essential role in the pathophysiology of diabetes and that targeting the α cell and glucagon are innovative approaches in the management of diabetes. Despite active research and identification of promising compounds, no one selective glucagon antagonist is presently used in the treatment of diabetes. Interestingly, besides insulin, several drugs used today in the management of diabetes appear to exert their effects, in part, by inhibiting glucagon secretion (glucagon-like peptide-1 receptor agonists, dipeptidyl peptidase-4 inhibitors, α-glucosidase inhibitors and, possibly, sulphonylureas) or glucagon action (metformin). The potential risks associated with total glucagon suppression include α-cell hyperplasia, increased mass of the pancreas, increased susceptibility to hepatosteatosis and hepatocellular injury and increased risk of hypoglycaemia, and these should be considered in the search and development of new compounds reducing glucagon receptor signalling. More than 40 years after its initial description, hyperglucagonaemia in diabetes can no longer be ignored or minimized, and its correction represents an attractive way to improve diabetes management.

Oscillatory membrane potential response to glucose in islet beta-cells: a comparison of islet-cell electrical activity in mouse and rat

In contrast to mouse, rat islet beta-cell membrane potential is reported not to oscillate in response to elevated glucose despite demonstrated oscillations in calcium and insulin secretion. We aim to clarify the electrical activity of rat islet beta-cells and characterize and compare the electrical activity of both alpha- and beta-cells in rat and mouse islets. We recorded electrical activity from alpha- and beta-cells within intact islets from both mouse and rat using the perforated whole-cell patch clamp technique. Fifty-six percent of both mouse and rat beta-cells exhibited an oscillatory response to 11.1 mm glucose. Responses to both 11.1 mm and 2.8 mm glucose were identical in the two species. Rat beta-cells exhibited incremental depolarization in a glucose concentration-dependent manner. We also demonstrated electrical activity in human islets recorded under the same conditions. In both mouse and rat alpha-cells 11 mm glucose caused hyperpolarization of the membrane potential, whereas 2.8 mm glucose produced action potential firing. No species differences were observed in the response of alpha-cells to glucose. This paper is the first to demonstrate and characterize oscillatory membrane potential fluctuations in the presence of elevated glucose in rat islet beta-cells in comparison with mouse. The findings promote the use of rat islets in future electrophysiological studies, enabling consistency between electrophysiological and insulin secretion studies. An inverse response of alpha-cell membrane potential to glucose furthers our understanding of the mechanisms underlying glucose sensitive glucagon secretion.

Glucagon: the effects of its excess and deficiency on insulin action

AIM

To review the role that glucagon plays in physiology, physiopathology and clinical medicine.

DATA SYNTHESIS

Glucagon assays employing specific radioimmunoassay (RIA) techniques are now widely used to characterize pathologic conditions where the effect of the excess or deficiency of glucagon on insulin actions might play a role. Glucagon excess counteracts the action of insulin on glucose metabolism by stimulating glycogenolysis and gluconeogenesis. Aside from glucagon excess in association with glucagonoma, glucagon excess is found in several metabolic disturbances. In diabetes mellitus, hyperglycaemia is the consequence of the glycogenolytic and gluconeogenic effects of glucagon excess occurring in the setting of a relative insulin deficiency (i.e. Type 2 diabetes), whereas excess of glucagon and absent insulin levels are typical features of diabetic ketoacidosis. Although plasma glucagon levels of patients with diabetes are usually increased relative to the prevailing plasma glucose concentrations, it is a paradox that in those patients glucagon levels fail to rise when hypoglycaemia develops. Since glucagon release is considered the primary defence against insulin-induced hypoglycaemia, the defective response of glucagon to hypoglycaemia may favour the development of severe hypoglycaemia. Such defective response to hypoglycaemia in diabetes can be regarded as a condition of selective glucagon deficiency the mechanisms of which remain to be elucidated.

CONCLUSION

The most common condition associated with glucagon excess or deficiency is diabetes mellitus. Glucagon excess contributes to hyperglycaemia whereas reduced glucagon response to insulin-induced hypoglycaemia promotes severe hypoglycaemia. It is expected that drugs that are able to reduce glucagon secretion in concert with strategies directed to recover glucagon secretion to hypoglycaemia might contribute to improve the overall glycaemic control in diabetes.

ATP-sensitive K+ channel-dependent regulation of glucagon release and electrical activity by glucose in wild-type and SUR1-/- mouse alpha-cells

Patch-clamp recordings and glucagon release measurements were combined to determine the role of plasma membrane ATP-sensitive K+ channels (KATP channels) in the control of glucagon secretion from mouse pancreatic alpha-cells. In wild-type mouse islets, glucose produced a concentration-dependent (half-maximal inhibitory concentration [IC50]=2.5 mmol/l) reduction of glucagon release. Maximum inhibition (approximately 50%) was attained at glucose concentrations >5 mmol/l. The sulfonylureas tolbutamide (100 micromol/l) and glibenclamide (100 nmol/l) inhibited glucagon secretion to the same extent as a maximally inhibitory concentration of glucose. In mice lacking functional KATP channels (SUR1-/-), glucagon secretion in the absence of glucose was lower than that observed in wild-type islets and both glucose (0-20 mmol/l) and the sulfonylureas failed to inhibit glucagon secretion. Membrane potential recordings revealed that alpha-cells generate action potentials in the absence of glucose. Addition of glucose depolarized the alpha-cell by approximately 7 mV and reduced spike height by 30% Application of tolbutamide likewise depolarized the alpha-cell (approximately 17 mV) and reduced action potential amplitude (43%). Whereas insulin secretion increased monotonically with increasing external K+ concentrations (threshold 25 mmol/l), glucagon secretion was paradoxically suppressed at intermediate concentrations (5.6-15 mmol/l), and stimulation was first detectable at >25 mmol/l K+. In alpha-cells isolated from SUR1-/- mice, both tolbutamide and glucose failed to produce membrane depolarization. These effects correlated with the presence of a small (0.13 nS) sulfonylurea-sensitive conductance in wild-type but not in SUR1-/- alpha-cells. Recordings of the free cytoplasmic Ca2+ concentration ([Ca2+]i) revealed that, whereas glucose lowered [Ca2+]i to the same extent as application of tolbutamide, the Na+ channel blocker tetrodotoxin, or the Ca2+ channel blocker Co2+ in wild-type alpha-cells, the sugar was far less effective on [Ca2+]i in SUR1-/- alpha-cells. We conclude that the KATP channel is involved in the control of glucagon secretion by regulating the membrane potential in the alpha-cell in a way reminiscent of that previously documented in insulin-releasing beta-cells. However, because alpha-cells possess a different complement of voltage-gated ion channels involved in action potential generation than the beta-cell, moderate membrane depolarization in alpha-cells is associated with reduced rather than increased electrical activity and secretion.

Palmitate stimulation of glucagon secretion in mouse pancreatic alpha-cells results from activation of L-type calcium channels and elevation of cytoplasmic calcium

We have investigated the short-term effects of the saturated free fatty acid (FFA) palmitate on pancreatic alpha-cells. Palmitate (0.5 or 1 mmol/l bound to fatty acid-free albumin) stimulated glucagon secretion from intact mouse islets 1.5- to 2-fold when added in the presence of 1-15 mmol/l glucose. Palmitate remained stimulatory in islets depolarized with 30 mmol/l extracellular K(+) or exposed to forskolin, but it did not remain stimulatory after treatment with isradipine or triacsin C. The stimulatory action of palmitate on secretion correlated with a 3.5-fold elevation of intracellular free Ca(2+) when applied in the presence of 15 mmol/l glucose, a 40% stimulation of exocytosis (measured as increases in cell capacitance), and a 25% increase in whole-cell Ca(2+) current. The latter effect was abolished by isradipine, suggesting that palmitate selectively modulates l-type Ca(2+) channels. The effect of palmitate on exocytosis was not mediated by palmitoyl-CoA, and intracellular application of this FFA metabolite decreased rather than enhanced Ca(2+)-induced exocytosis. The stimulatory effects of palmitate on glucagon secretion were paralleled by a approximately 50% inhibition of somatostatin release. We conclude that palmitate increases alpha-cell exocytosis principally by enhanced Ca(2+) entry via l-type Ca(2+) channels and, possibly, relief from paracrine inhibition by somatostatin released by neighboring delta-cells.

Effect of two antihypertensive combinations on metabolic control in type-2 diabetic hypertensive patients with albuminuria: a randomised, double-blind study

The objective of this study was to compare, at equal blood pressure (BP) reduction, the effect of two different combinations on metabolic control and albuminuria in type 2 diabetic hypertensive patients with albuminuria. This was a prospective, randomised, double-blind, parallel, controlled trial carried out in 11 Spanish hospitals. A total of 103 type 2 diabetic patients with stable albuminuria and BP not controlled on monotherapy were randomised of which 93 finished the study. After a 4-week single-blind placebo period, patients were randomised to verapamil SR/trandolapril 180/2 mg (VT) or to enalapril/hydroclorothiazide 20/12.5 mg (EH). Treatment duration was 6 months. The main outcome measures were changes in BP, 24-h albuminuria, blood glucose and glycated haemoglobin. Overall BP was significantly reduced from 157.3 +/- 12.0/98.3 +/- 6.4 mm Hg to 140.5 +/- 14.5/86.1 +/- 8.2 mm Hg (P < 0.001) and albuminuria significantly decreased from 508.6 +/- 693.8 mg/24 h to 253.4 +/- 517.2 mg/24 h (P < 0.001), both without significant differences between treatments. Glycated haemoglobin was not modified on VT: baseline, 5.91 +/- 1.43%; end of treatment, 5.94 +/- 1.62%, but increased on EH: baseline, 5.96 +/- 1.25%; final, 6.41 +/- 1.51%, (ANOVA interaction P = 0.040). At the end of the study, a blood glucose <126 mg/dL was attained in 72.7% of the VT group-improving in 29.5% and worsening in 6.8% of patients (P = 0.021)-and in 50% of the EH group, 13.6% of patients improved and 11.4% worsened (P = 1.000). There were no changes in body weight, serum creatinine, uric acid, potassium, cholesterol, tryglicerides and serum albumin. In hypertensive type 2 diabetic patients not controlled on monotherapy, both treatments similarly reduced albuminuria. The combination verapamil/ trandolapril seems to allow a better metabolic control than enalapril/hydroclorothiazide.

Indirect effect of insulin to suppress endogenous glucose production is dominant, even with hyperglucagonemia

Suppression of endogenous glucose production (EGP) is one of insulin's primary metabolic effects and failure of this action is a major contributor to fasting hyperglycemia of type 2 diabetes mellitus. Classically, insulin was thought to suppress the liver directly, via hyperinsulinemia in the portal vein. Recently, however, we and others have demonstrated that at least part, and possibly most of insulin's action to suppress EGP is normally mediated via an extrahepatic (i.e., indirect) mechanism. We have suggested that this mechanism involves insulin suppression of adipocyte lipolysis, leading to lowered FFA and reduced EGP ("Single Gateway Hypothesis"). Previous studies of the indirect insulin effect from this laboratory were done under conditions of lowered portal glucagon. Because of the possibility that the direct (i.e., portal) effect of insulin may have been underestimated with hypoglucagonemia, these studies examined the relative importance of portal insulin, versus peripheral insulin (administered at one-half the dose to equalize peripheral insulin levels) at four rates of portal glucagon infusion: 0, 0.65 (under-), 1.5 (basal-), and 3.0 ng/kg per min (over-replacement). Portal versus peripheral insulin suppressed steady-state EGP to the same extent (52%), confirming that the primary effect of insulin to suppress EGP is via the peripheral mechanism. This conclusion was maintained regardless of portal glucagonemia, although there was some evidence for an increase in the direct insulin effect at hyperglucagonemia. The indirect effect of insulin is the primary mechanism of steady-state EGP suppression under normal conditions. The direct effect increases with hyperglucagonemia; however, the indirect effect remains predominant even under those conditions.

Failure of glucagon suppression contributes to postprandial hyperglycaemia in IDDM

Carbohydrate ingestion results in a fall in glucagon concentration in non-diabetic but not in diabetic individuals. To determine if, and the mechanism by which, lack of postprandial suppression of glucagon contributes to hyperglycaemia, nine subjects with insulin-dependent diabetes mellitus (IDDM) ingested 50 g of glucose containing both [2-3H] glucose and [6-3H] glucose on two occasions. [6-14C] glucose, insulin and low-dose somatostatin were infused intravenously at the same rates on both occasions. A basal glucagon infusion was started either at the same time ("constant glucagon") or 2 h following ("suppressed glucagon") glucose ingestion. This resulted in lower (p < 0.001) glucagon concentrations during the first 2 h of the suppressed than during the constant glucagon study days (63 +/- 1 vs 108 +/- 2 pg/ml). Lack of suppression of glucagon led to higher (p < 0.01) postprandial glucose concentrations (10.3 +/- 0.9 vs 8.1 +/- 0.7 mmol/l) and a greater (p < 0.02) integrated glycaemic response. The excessive rise in glucose was due to higher (p < 0.02) rates of postprandial hepatic glucose release during the constant than during the suppressed glucagon study days, whether measured using either [6-3H] glucose (2.6 +/- 0.2 vs 2.0 +/- 0.2 mmol.kg-1 per 6 h) or [2-3H] glucose (3.0 +/- 0.3 vs 2.4 +/- 0.2 mmol.kg-1 per 6 h) as the meal tracer. Glucose disappearance, initial splanchnic glucose clearance and hepatic glucose cycling did not differ on the two occasions. Thus, the present studies demonstrate that lack of postprandial suppression of glucagon, by increasing hepatic glucose release, contributes to hyperglycaemia in subjects with IDDM.

Abnormal glucagon response to arginine and its normalization in obese hyperinsulinaemic patients with glucose intolerance: importance of insulin action on pancreatic alpha cells

An excessive glucagon secretion to intravenous arginine infusion was found in obese hyperinsulinaemic patients with glucose intolerance. This study was designed to determine whether the glucagon hyperresponsiveness to arginine in these patients would improve by insulin infused at a high enough dose to overcome insulin resistance. By infusing high dose insulin during arginine infusion, the previously exaggerated glucagon response to arginine could be normalized. To normalize the abnormal glucagon response, insulin doses of 4.2 +/- 0.7 and 3.8 +/- 0.5 IU were required during arginine infusion in obese hyperinsulinaemic patients with impaired glucose tolerance and Type 2 (non-insulin-dependent) diabetes mellitus, respectively. This achieved plasma peak insulin levels 3 to 4 times higher than those observed in non-obese healthy subjects. Furthermore, we clarified whether or not the effect of normalizing insulin action and/or glycaemic excursions contributed to normalizing the exaggerated glucagon response to arginine in these patients. Blood glucose was clamped while high dose insulin was infused at the same levels as observed during the arginine infusion test with no insulin infusion. As a result, normalization of the exaggerated plasma glucagon response was achieved, whether hyperglycaemia existed or not. These results clearly demonstrate that, similar to non-obese hypoinsulinaemic Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetic patients, the exaggerated Alpha-cell response to arginine infusion in obese hyperinsulinaemic patients with glucose intolerance is secondary to the reduction of insulin action on the pancreatic Alpha cell, and that the expression of insulin action plays an important part in normalizing these abnormalities.

Serum ketone response to glucagon as a marker of insulin dependency in diabetics

The serum ketone response to glucagon was measured in 10 patients with IDDM and 37 with NIDDM. In both groups, serum 3-hydroxybutyrate increased significantly after intravenous injection of 1 mg glucagon. The difference between the serum level of 3-hydroxybutyrate at 30 min and basal level [delta 3-OHBA(30')] was 133 +/- 25 mumol/l in the patients with IDDM, 13 +/- 8 mumol/l in those with NIDDM treated by diet alone or with oral hypoglycemic agents and 23 +/- 13 mumol/l in those with NIDDM treated with insulin. The delta 3-OHBA(30') was significantly greater in IDDM patients than in both groups of NIDDM patients (P less than 0.001). The delta 3-OHBA(30') was greater than 87 mumol/l in eighty percent of IDDM patients, but smaller than 87 mumol/l in both groups of NIDDM patients. The delta 3-OHBA(30') was correlated with the difference between the plasma level of C-peptide at 6 min and basal level [delta CPR(6')] (r = -0.540, P less than 0.001). The delta 3-OHBA(30') was not correlated with fasting plasma levels of glucose, fructosamine or hemoglobin A1c. These observations show that measurement of the serum ketone response to glucagon is a useful marker of insulin dependency. In order to determine insulin dependency, the simultaneous measurement of concentrations of ketones and C-peptide is indicated during the glucagon stimulation test.

Glucagon responses to intravenous arginine and oral glucose in insulin-dependent diabetic patients during six months conventional or continuous subcutaneous insulin infusion

To elucidate the impact of subcutaneous insulin infusion (CSII) treatment on the glucagon response to intravenous (IV) arginine and to oral glucose a 6-month prospective randomized study in insulin-dependent diabetics was carried out. The effects were investigated of CSII (7-patients) and conventional insulin treatment (UCT) (9 patients) on the changes in glucagon, growth hormone, glucose, lactate, glycerol, 3-hydroxybutyrate, and alanine to IV arginine and to oral glucose in insulin-dependent diabetics who were made euglycemic and isoinsulinemic using the artificial pancreas (Biostator, Miles, Elkhart, IN). HbA1c was significantly lower in the group treated by CSII. Despite the improved glycemic control no significant change in the responses of A-cell secretion to arginine or glucose challenges was found. In addition, there were no significant differences in hormone or metabolite values between the two groups at entry to the study or after 6 months of either therapy. Thus, normalization of the A-cell sensitivity to glucose in insulin-dependent diabetic subjects requires further amelioration of the intermediary metabolism than can be achieved with insulin pump treatment.

Influence of verapamil on human glucose tolerance

Studies have indicated that verapamil inhibits insulin release from pancreatic beta cells in vitro. Studies in this clinic, however, showed that both oral pretreatment with verapamil for 1 week and intravenous infusion of the drug over a period of 3 hours improved oral glucose tolerance in patients with type II diabetes without affecting insulin release. In contrast, verapamil failed to increase further the hypoglycemic effect of oral glibenclamide therapy when administered intravenously in diabetic patients. This hypoglycemic effect of verapamil does not appear to be caused by reduced glucose absorption from the gut because intravenous infusion of verapamil left the portal vein glucose response to glucose ingestion unaffected in normoglycemic patients who underwent portal vein catheterization for diagnostic purposes. It is more likely that verapamil affects the liver, leading to decreased hepatic glucose output, which supports previous reports that have shown an inhibitory influence of verapamil on enzymes involved in the gluconeogenetic and glycogenolytic processes.

Prevalence of morning hyperglycaemia: determinants of fasting blood glucose concentrations in insulin-treated diabetics

A rise in blood glucose concentration at the end of the night, and consequent morning hyperglycaemia, are well recognized events in some diabetic patients. In 94 patients on twice daily insulin injections we have examined the prevalence and extent of morning hyperglycaemia, and its relation to control, insulin therapy, and insulin antibody levels. Blood glucose reached the highest level of the day before or after breakfast in 83% of patients, and in 50% this value was 2 mmol/l greater than any other time of day. Patients with higher fasting concentrations did not have worse blood glucose control over the rest of the day. No correlation was found between fasting blood glucose concentrations and the evening dose of intermediate acting insulin or the level of insulin antibodies. No consistent change in fasting blood glucose concentrations occurred with changes in antibody levels in patients switched between pork and beef insulin. Morning hyperglycaemia was as common with both insulin species. Pre- and post-breakfast hyperglycaemia is common and significant in insulin-treated diabetic patients. It is not directly related to diabetic control at other times of the day, and is independent of insulin species and insulin antibody levels.

Plasma glucagon suppressibility after oral glucose in obese subjects with normal and impaired glucose tolerance

Blood glucose, plasma insulin, and glucagon responses after a 75 g oral glucose-tolerance test were assessed in 9 normal controls, 5 obese nondiabetics (ON), 5 obese nondiabetics with fasting hyperinsulinemia (obese "resistant" nondiabetics--OR), 9 obese with impaired glucose tolerance (O-IGT), and 9 nonobese insulin-dependent diabetics (IDD). Fasting plasma glucagon concentrations were significantly higher in all groups of patients in comparison to the normal controls. Insulin secretion, evaluated in all but the IDD, was similar to normal in the ON and increased in the OR and O-IGT. Normal glucagon suppression was observed in the lean controls and ON but not in OR, O-IGT, and IDD. We suggested that the resistance to glucagon suppression after glucose load in the OR and O-IGT in the presence of increased insulin response could be an indication that the A cell participates in the relative insulin insensitivity of these subjects.

Glucagon stimulates ketone utilization by rat brain slices

Glucagon has been shown previously to increase further the enhanced tolerance for hypoxia observed in mice with elevated blood ketones. Glucagon is also known to increase blood glucose and to alter directly the metabolism of some (liver) cells. Both the increase in blood glucose and altered cellular metabolism could contribute to the increase in tolerance for hypoxia observed in mice given glucagon in combination with the ketone, beta-hydroxybutyrate. To evaluate the systemic component of this hypothesis, blood glucose, beta-hydroxybutyrate, and glucagon were elevated alone or simultaneously and hypoxic tolerance of mice was measured. To identify possible cellular effects of glucagon on glucose or ketone metabolism, we measured the incorporation of radiolabeled glucose or beta-hydroxybutyrate into CO2 or total lipid in isolated rat brain slices. Both glucagon and glucose increased hypoxic tolerance of ketotic mice but our data do not support the hypothesis that glucagon's action was only through an elevation of blood glucose. In brain slices glucagon stimulated the incorporation of beta-hydroxybutyrate into CO2 both in the presence or absence of additional glucose. These results demonstrate that glucagon has a direct effect on brain metabolism which may contribute to the increased tolerance for hypoxia. They, however, do not exclude the possibility that glucagon is working in addition to increase hypoxic survival in ketotic mice by increasing the availability of glucose to the brain.

Influence of obesity on basal glucagon levels in non-diabetic and diabetic Nauruans

Basal plasma glucagon (IRG), insulin (IRI) and glucose levels were measured in normal weight (Body Mass Index (BMI) less than 30) and obese (BMI greater than or equal to 30) non-diabetic and diabetic Micronesians (n = 30) on Nauru Island. This population has a high prevalence of diabetes mellitus. IRG levels were significantly higher (P less than 0.02) in the non-diabetic obese, compared to the non-diabetic lean subjects (109 +/- 19 vs 44 +/- 12 SEM pg/ml, respectively) and there was a significant positive correlation between basal IRG and BMI (r = 0.79, P less than 0.001). IRG levels were similar in diabetic obese and diabetic lean subjects. The pathophysiological significance of the hyperglucagonaemia in these obese subjects is not known, although it may be related to the frequent development of diabetes in this unique population.

Mammalian pancreatic preproglucagon contains three glucagon-related peptides

We have isolated cDNA clones encoding bovine pancreatic preproglucagon. Twenty-five putative preproglucagon clones were selected by screening 3,100 clones of a fetal bovine pancreas cDNA library with a synthetic oligodeoxynucleotide probe. The probe was a mixture of synthetic 17-base DNA oligomers constructed to correspond to the six carboxyl-terminal amino acids (residues 24-29) of mature glucagon. Restriction mapping of six of these clones suggested that they represented a single mRNA species. Primary sequence analysis of one clone containing a 1,200-base-pair DNA insert revealed that it contained an essentially full-length copy of glucagon mRNA. Analysis of the cDNA suggested a protein coding sequence of 540 nucleotides and 5'- and 3'-untranslated regions of 90 and 471 nucleotides, respectively. This cDNA sequence encoded a 20-amino acid signal sequence followed by one for glicentin, a 69-amino acid polypeptide containing an internal glucagon moiety that has been found in porcine intestines. Glicentin is followed by two additional glucagon-like peptides, each flanked by paired basic amino acids (Lys, Arg) characteristic of prohormone processing. These polypeptide sequences show striking homology with those for glucagon and other members of the glucagon family of peptides.

Intermediate acting insulin given at bedtime: effect on blood glucose concentrations before and after breakfast

Six C-peptide deficient diabetics receiving twice daily mixtures of short and intermediate acting insulins were selected for study because of persistently raised blood glucose concentrations before and after breakfast. They were investigated to assess the effect of moving their evening injection of intermediate acting insulin to bedtime. The patients' usual twice daily insulin treatment was optimised and compared with the bedtime regimen during inpatient metabolic studies and an outpatient crossover study. With the conventional injection regimen blood glucose concentration rose sharply from 0500 to reach a fasting mean value of 10 +/- SE 1 . 6 mmol/l (180 +/- 29 mg/100 ml) and 16 . 8 +/- 2 . 2 mmol/l (303 +/- 40 mg/100 ml) after breakfast. By contrast, when the evening dose of intermediate acting insulin was delayed until bedtime the nocturnal rise in blood glucose concentration started later and was significantly lower both fasting (7 . 5 +/- 1 . 1 mmol/l (135 +/- 20 mg/100 ml); p less than 0 . 02) and after breakfast (13 . 2 +/- 1 . 4 mmol/l(238 +/- 25 mg/100 ml); p less than 0 . 02). Fasting blood concentrations of ketone bodies (3-hydroxybutyrate) were also significantly decreased. Plasma free insulin concentrations showed the predicted changes in five of the six patients. Blood glucose profiles collected over four months during the outpatient study confirmed the beneficial effect of giving intermediate acting insulin at bedtime.

Metabolic interactions of glucagon and cortisol in man--studies with somatostatin

The metabolic response to pathophysiologic concentrations of glucagon, induced by glucagon infusion, has been examined in normal man before and after 36-60 hr hypercortisolaemia, induced by administration of tetracosactrin-depot. Glucagon alone increased serum insulin levels twofold but blood glucose was unaltered. Plasma NEFA and blood ketone body concentrations were decreased by glucagon infusion. Tetracosactrin produced a threefold rise in serum cortisol levels and caused mild fasting hyperglycemia and hyperinsulinaemia. Subsequent glucagon infusion had no effect on circulating insulin, glucose, NEFA or ketone body concentrations. Simultaneous infusion of somatostatin, to produce partial insulin-deficiency, unmasked a hyperglycemic action of glucagon (+ 3.8 +/- 0.2 mmol/l at 90 min, p less than 0.02). This glucagon-induced rise in blood glucose was diminished by prior tetracosactrin administration. Tetracosactrin revealed a mild lipolytic action of glucagon in partial insulin deficiency, not apparent in the euadrenal state. Glucagon was equally hyperketonemic during somatostatin infusion before and after tetracosactrin. Thus the hyperglycemic and hyperketonemic actions of glucagon at pathophysiologic levels are restricted to insulin deficiency. Hypercortisolaemia reveals a lipolytic action of glucagon in insulin-deficient man but does not potentiate the hyperglycemic or hyperketonemic effects.

Effects of guar on plasma viscosity and related parameters in diabetic children

Ten diabetic children supplemented their normal diets with 0.45 g/kg/day guar gum for 4 weeks. They experienced a decrease in (1) plasma fibrinogen, (2) insulin requirement, (3) serum osmolality and (4) plasma viscosity; and an increase in serum albumin and total serum protein concentrations. The decrease in plasma viscosity, which was statistically significant, depended on the increase of albumin and the decrease of fibrinogen and may have some significance to the development of diabetic microangiopathy. The sequence of events eventually leading to a decrease of plasma viscosity is possibly mediated by gip and glucagon, consecutively.

The acute metabolic effects of glucagon and its interactions with insulin in forearm tissue

The acute effects of glucagon (mol. wt. 3500) and its interactions with insulin were studied in the forearm during eight studies in seven normal, post-absorptive males. The protocol consisted of a 2 h baseline, 1 h glucagon perfusion (mean glucagon increment, 691 +/- 50 pg/ml), 1 h perfusion of both insulin and glucagon (mean insulin increment of 105 insulin and glucagon (mean insulin increment of 105 /- 13 mU/l) and a 30 min recovery period. Simultaneous arterial (A), deep venous (DV), and superficial venous (SV) blood samples were obtained at 30 min intervals. Perfusion of glucagon resulted in a decrease in (A-DV) non-esterified fatty acids of -0.128 +/- 0.057 mmol/l (n = 7, p less than 0.05) and (A-SV) non-esterified fatty acids of -0.081 +/- 0.36 mol/l (n = 7, p less than 0.05), as well as a change in deep compartment uptake of glycerol after 60 min of -0.044 +/- 0.019 mumol/min/100 ml of forearm tissue (n=6, p less than 0.05), indicating increased lipolysis. There was also a decrease in net glucose uptake as reflected by a change in (A-Dids of -0.081 +/- 0.36 mol/l (n = 7, p less than 0.05), as well as a change in deep compartment uptake of glycerol after 60 min of -0.044 +/- 0.019 mumol/min/100 ml of forearm tissue (n=6, p less than 0.05), indicating increased lipolysis. There was also a decrease in net glucose uptake as reflected by a change in (A-Dids of -0.081 +/- 0.36 mol/l (n = 7, p less than 0.05), as well as a change in deep compartment uptake of glycerol after 60 min of -0.044 +/- 0.019 mumol/min/100 ml of forearm tissue (n=6, p less than 0.05), indicating increased lipolysis. There was also a decrease in net glucose uptake as reflected by a change in (A-DV) of -0.24 +/- 0.09 mmol/l (n = 7, p less than 0.025) and (A-SV) of 0.10 +/- 0.05 mmol/l (n = 7, p less than 0.05). There was also a net decrease in deep arteriovenous differences of potassium in six of seven subjects. Insulin levels, similar to those found after a meal, rapidly reversed the effects of glucagon on non-esterified fatty acid, glucose and potassium. These effects persisted throughout the recovery period.

Reversal of impaired GIP and insulin secretion in patients with pancreatogenic steatorrhea following enzyme substitution

The influence of impaired digestion on nutrient induced release of gastric inhibitory polypeptide (GIP) and insulin have been investigated in patients with chronic pancreatitis. All patients had massive steatorrhea (> 25 g/24 h), and glucose intolerance. A standard liquid test meal comprising fat and glucose were ingested with or without pancreatic enzyme substitution (9.0 g pancreatin). In the presence of pancreatin the response of serum levels of GIP to the test meal was significantly enhanced (81.2 vs 194.5 microgram/l X 180 min). Concurrently, the insulin response was augmented (3.4 vs 6.4 U/l X 180 min), resulting in improved glucose tolerance. Addition of pancreatin also significantly augmented the GIP response to oral fat (100 g), but not to oral glucose (100 g). In patients with pancreatogenic steatorrhea the insulin response to an IV glucose infusion (0.7 g/kg/h for 90 min) was augmented by oral fat only after addition of 9.0 g pancreatin to the fat load (3.5 vs 7.3 U/l X 180 min). After restoration of the GIP response to fat by pancreatin, the inhibitory effect of IV glucose on fat-induced GIP increase was restored. These data indicate that the GIP response to a mixed meal or triglycerides is dependent on the absorption of nutrients. In patients with chronic pancreatitis improvement of pancreatogenic insufficiency reverses the impaired GIP response, restores the incretin effect of fat, and improves glucose tolerance.

Effects of glucagon and pentagastrin on glibenclamide-induced insulin release

It was recently reported that administration of sulphonylureas may lead to a stimulation of the release of glucagon and a gastrin-like peptide. These peptides may then eventually influence the insulin releasing action of the sulphonylureas. Therefore, the effects of glucagon and pentagastrin on basal and glibenclamide-induced insulin secretion were studied. It was found that at a dose of 4.25 nmol/kg the two peptides induced a significant stimulation of basal insulin secretion. However, pentagastrin at the dose of 4.25 nmol/kg did not influence the insulin release induced by glibenclamide, whereas an equimolar dose of glucagon potentiated the insulin secretory response to this sulphonylurea drug by about 40%. Glucagon in contrast to pentagastrin thus positively modulates the insulin secretory pathway stimulated by the sulphonylurea drug glibenclamide.