Lack of glucagon response in glucose counter-regulation in type 1 (insulin-dependent) diabetics: absence of recovery after prolonged optimal insulin therapy

The past, present, and future physiology and pharmacology of glucagon

The evolution of glucagon has seen the transition from an impurity in the preparation of insulin to the development of glucagon receptor agonists for use in type 1 diabetes. In type 2 diabetes, glucagon receptor antagonists have been explored to reduce glycemia thought to be induced by hyperglucagonemia. However, the catabolic actions of glucagon are currently being leveraged to target the rise in obesity that paralleled that of diabetes, bringing the pharmacology of glucagon full circle. During this evolution, the physiological importance of glucagon advanced beyond the control of hepatic glucose production, incorporating critical roles for glucagon to regulate both lipid and amino acid metabolism. Thus, it is unsurprising that the study of glucagon has left several paradoxes that make it difficult to distill this hormone down to a simplified action. Here, we describe the history of glucagon from the past to the present and suggest some direction to the future of this field.

Pharmacological therapies to address obesity in type 1 diabetes

PURPOSE OF REVIEW

Obesity is increasing in prevalence among patients with type 1 diabetes (T1D) and is associated with insulin resistance and increased cardiovascular risk. The management of obesity in this population is complicated by defects in pancreatic islet hormone secretion and the effects of exogenous insulin treatment. Here, we review the effects of antiobesity medications and adjunct-to-insulin medications on body weight in T1D.

RECENT FINDINGS

There is a profound evidence gap around the use of drugs for the treatment of obesity in T1D since systematic studies have not been performed in this population. Adjunctive-to-insulin therapy with certain antihyperglycemic agents leads to modest weight loss and reductions in insulin dose in T1D. However, only pramlintide has been approved in the United States for clinical use as adjunctive therapy in T1D.

SUMMARY

The growing prevalence of obesity in T1D has created an unmet need for safe and effective therapies to treat overweight and obesity in this population. Currently, antiobesity medications are used off-label for the treatment of patients with T1D. Additional studies are needed to understand the role of these medications in the management of obesity in patients with T1D.

GPR119 Agonism Increases Glucagon Secretion During Insulin-Induced Hypoglycemia

Insulin-induced hypoglycemia in diabetes is associated with impaired glucagon secretion. In this study, we tested whether stimulation of GPR119, a G-protein-coupled receptor expressed in pancreatic islet as well as enteroendocrine cells and previously shown to stimulate insulin and incretin secretion, might enhance glucagon secretion during hypoglycemia. In the study, GPR119 agonists were applied to isolated islets or perfused pancreata to assess insulin and glucagon secretion during hypoglycemic or hyperglycemic conditions. Insulin infusion hypoglycemic clamps were performed with or without GPR119 agonist pretreatment to assess glucagon counterregulation in healthy and streptozotocin (STZ)-induced diabetic rats, including those exposed to recurrent bouts of insulin-induced hypoglycemia that leads to suppression of hypoglycemia-induced glucagon release. Hypoglycemic clamp studies were also conducted in GPR119 knockout (KO) mice to evaluate whether the pharmacological stimulatory actions of GPR119 agonists on glucagon secretion during hypoglycemia were an on-target effect. The results revealed that GPR119 agonist-treated pancreata or cultured islets had increased glucagon secretion during low glucose perfusion. In vivo, GPR119 agonists also significantly increased glucagon secretion during hypoglycemia in healthy and STZ-diabetic rats, a response that was absent in GPR119 KO mice. In addition, impaired glucagon counterregulatory responses were restored by a GPR119 agonist in STZ-diabetic rats that were exposed to antecedent bouts of hypoglycemia. Thus, GPR119 agonists have the ability to pharmacologically augment glucagon secretion, specifically in response to hypoglycemia in diabetic rodents. Whether this effect might serve to diminish the occurrence and severity of iatrogenic hypoglycemia during intensive insulin therapy in patients with diabetes remains to be established.

Inhaled Formoterol Diminishes Insulin-Induced Hypoglycemia in Type 1 Diabetes

OBJECTIVE

Hypoglycemia is one of the major factors limiting implementation of tight glycemic control in patients with type 1 diabetes and is associated with increased morbidity and mortality during intensive insulin treatment. β-2 Adrenergic receptor (AR) agonists have been reported to diminish nocturnal hypoglycemia; however, whether long-acting inhaled β-2 AR agonists could potentially be used to treat or prevent hypoglycemia has not been established.

RESEARCH DESIGN AND METHODS

Seven patients with type 1 diabetes and seven healthy control subjects received inhaled formoterol (48 μg), a highly specific β-2 AR agonist, or a placebo during a hyperinsulinemic-hypoglycemic clamp study to evaluate its capacity to antagonize the effect of insulin. In a second set of studies, five subjects with type 1 diabetes received inhaled formoterol to assess its effect as a preventive therapy for insulin-induced hypoglycemia.

RESULTS

During a hyperinsulinemic-hypoglycemic clamp, compared with placebo, inhaled formoterol decreased the glucose infusion rate required to maintain plasma glucose at a target level by 45-50% (P < 0.05). There was no significant effect on glucagon, epinephrine, cortisol, or growth hormone release (P = NS). Furthermore, in volunteers with type 1 diabetes 1 h after increasing basal insulin delivery twofold, glucose levels dropped to 58 ± 5 mg/dL, whereas hypoglycemia was prevented by inhaled formoterol (P < 0.001).

CONCLUSIONS

Inhalation of the β-2 AR-specific agonist formoterol may be useful in the prevention or treatment of acute hypoglycemia and thus may help patients with type 1 diabetes achieve optimal glucose control more safely.

Glucagon-reactive islet-infiltrating CD8 T cells in NOD mice

Type 1 diabetes is characterized by T-cell-mediated destruction of the insulin-producing β cells in pancreatic islets. A number of islet antigens recognized by CD8 T cells that contribute to disease pathogenesis in non-obese diabetic (NOD) mice have been identified; however, the antigenic specificities of the majority of the islet-infiltrating cells have yet to be determined. The primary goal of the current study was to identify candidate antigens based on the level and specificity of expression of their genes in mouse islets and in the mouse β cell line MIN6. Peptides derived from the candidates were selected based on their predicted ability to bind H-2K(d) and were examined for recognition by islet-infiltrating T cells from NOD mice. Several proteins, including those encoded by Abcc8, Atp2a2, Pcsk2, Peg3 and Scg2, were validated as antigens in this way. Interestingly, islet-infiltrating T cells were also found to recognize peptides derived from proglucagon, whose expression in pancreatic islets is associated with α cells, which are not usually implicated in type 1 diabetes pathogenesis. However, type 1 diabetes patients have been reported to have serum autoantibodies to glucagon, and NOD mouse studies have shown a decrease in α cell mass during disease pathogenesis. Our finding of islet-infiltrating glucagon-specific T cells is consistent with these reports and suggests the possibility of α cell involvement in development and progression of disease.

Glucose transport in brain and retina: implications in the management and complications of diabetes

Neural tissue is entirely dependent on glucose for normal metabolic activity. Since glucose stores in the brain and retina are negligible compared to glucose demand, metabolism in these tissues is dependent upon adequate glucose delivery from the systemic circulation. In the brain, the critical interface for glucose transport is at the brain capillary endothelial cells which comprise the blood-brain barrier (BBB). In the retina, transport occurs across the retinal capillary endothelial cells of the inner blood-retinal barrier (BRB) and the retinal pigment epithelium of the outer BRB. Because glucose transport across these barriers is mediated exclusively by the sodium-independent glucose transporter GLUT1, changes in endothelial glucose transport and GLUT1 abundance in the barriers of the brain and retina may have profound consequences on glucose delivery to these tissues and major implications in the development of two major diabetic complications, namely insulin-induced hypoglycemia and diabetic retinopathy. This review discusses the regulation of brain and retinal glucose transport and glucose transporter expression and considers the role of changes in glucose transporter expression in the development of two of the most devastating complications of long-standing diabetes mellitus and its management.

Human insulin induces a higher glucagon response to induced hypoglycemia in short normal children, compared to porcine insulin

After transfer of diabetic patients from porcine to human insulin, many reports emerged supporting an increased hypoglycemia unawareness. Several studies were then undertaken in both diabetic and healthy adults to investigate counterregulatory hormone responses to both porcine and human insulin-induced hypoglycemia as a possible underlying cause for this different hypoglycemia awareness. Most studies demonstrated similar neuroendocrine responses to both insulin species in adults. However, no such studies have ever been performed in healthy children. We undertook a double-blinded study of counterregulatory hormone responses to both porcine and human insulin-induced hypoglycemia in 17 short normal children randomly assigned to two groups, one receiving human and the other porcine insulin. We found similar responses of growth hormone, cortisol, epinephrine, norepinephrine and dopamine to both porcine insulin- and human insulin- induced hypoglycemia. Interestingly, we observed a significantly higher glucagon secretion when hypoglycemia was induced by human insulin. In conclusion, human insulin induces a higher glucagon secretion in healthy children than porcine insulin. Evidently, this observation cannot be extrapolated to diabetic patients. This study, however, further underlines the importance of performing investigations in children, since results found in adults differ from those observed in children.

Quantitative measurement of islet glucagon response to hypoglycemia by confocal fluorescence imaging in diabetic rats: effects of phlorizin treatment

We have shown that the glucagon irresponsiveness to hypoglycemia in diabetic rats is markedly improved by correction of hyperglycemia independent of insulin. In contrast, normalization of glycemia by insulin did not improve this response. To find out whether these glucagon responses reflect changes in islet glucagon, we directly quantified glucagon area and content in each pancreatic islet by using fluorescent immunostaining and computerized image analysis with confocal laser scanning microscopy (CLSM). The pancreases were analyzed in four groups of rats. 1. Normal controls (NC, n = 4), streptozotocin (65 mg/kg) diabetic rats. 2. Diabetic untreated (DU, n = 4). 3. Diabetic Phlorizin-treated, (0.4 g/kg), twice daily for 4 d (DP, n = 4). 4. Diabetic insulin-treated, using sustained release (2-3 U/d) insulin implant for 5 d (DI, n = 4). Basal plasma glucose was 7.4 +/- 0.3 mM in NC, increased to 14.5 +/- 2.2 mM in DU, which was normalized in DP (5.5 +/- 0.5) and DI (6.7 +/- 0.8). Acute hypoglycemia (H) was induced by i.v. insulin injection. The rats were sacrificed 2 h after insulin injection and the pancreas was removed. By imaging with CLSM, we quantified: 1. Percent of glucagon containing A-cell area/islet area, 2. Fluorescence intensity per islet area, which indicated glucagon content in the islet. 3. Fluorescence intensity per glucagon area indicating glucagon concentration in A-cells. In NC, glucagon containing A cell area was 21 +/- 2% of the islet area, and glucagon intensity and concentration was 11 +/- 1 U and 36 +/- 3.0 U, respectively, in basal (O) state and did not change in (H). In DU, glucagon area increased 183% (O) and 166% (H), and islet glucagon intensity increased by 235% (O) (p < 0.05), but decreased to 135% in H. Glucagon area in DP and DI did not differ significantly from DU. However, hypoglycemia in DP increased glucagon intensity in islet further to 306% of normal control (p < 0.05), suggesting marked increase in glucagon content indicating increased synthesis. In contrast, DI compared to DP showed a decrease in glucagon intensity in islet (46 +/- 3, DP to 22 +/- 2 DI; p < 0.05) in (H) state. Glucagon concentration followed the same pattern as its intensity.

CONCLUSION

1. Increase in islet glucagon content in diabetic rats was associated with increase in glucagon containing A-cell area per islet. 2. Phlorizin-induced insulin independent correction of hyperglycemia increased glucagon content per islet in hypoglycemic state. This, in part, probably contributed to improved glucagon response to hypoglycemia observed earlier 3. Normalization of glycemia with insulin reduced glucagon content of each islet during hypoglycemia. This may explain, in part, unresponsiveness of glucagon to hypoglycemia often observed in insulin-dependent diabetes mellitus (IDDM) with intensive insulin therapy.

Time course of the defective alpha-cell response to hypoglycemia in diabetic BB rats

Although it is understood that patients with insulin-dependent diabetes mellitus (IDDM) lose the ability to release glucagon during a hypoglycemic challenge, the relationship of this defect to the disease onset and loss of beta-cell function is not well defined. To address this issue, we measured the counterregulatory response in three groups of BB/wor rats during sequential 90-minute euglycemic (7 mmol/L) and hypoglycemic (3 mmol/L) insulin clamps (180 pmol/kg.min). Group 1 (n = 8) consisted of nondiabetic BB rats (aged 84 +/- 3 days), and groups 2 and 3 were rats studied 1 day (n = 7) or 7 days (n = 6) after diabetes onset. Plasma glucagon concentrations were similar in all groups during euglycemia (244 +/- 47 ng/L for nondiabetic, 308 +/- 38 for 1 day of diabetes, and 277 +/- 30 for 7 days of diabetes). Moreover, after 1 day of diabetes, the increase in plasma glucagon during hypoglycemia was similar to that seen in controls (to 581 +/- 94 and 650 +/- 118 ng/L, respectively) even though insulin production by the pancreas was virtually absent. However, after 7 days of diabetes, plasma glucagon only increased to 339 +/- 59 ng/L during hypoglycemia (P = nonsignificant v basal), despite normal pancreatic glucagon content (11.5 +/- 1.2 v 10.8 +/- 0.6 micrograms/g in nondiabetic controls). In conclusion, the hypoglycemia-associated defect in glucagon release occurs early in the course of diabetes in BB rats and is not associated with decreased baseline plasma or pancreatic glucagon levels. This impairment, although not immediately linked to the decrease in pancreatic insulin content, occurs soon afterward, implying that the two events are related.

Cephalic-phase insulin and glucagon release in normal subjects and in patients receiving pancreas transplantation

The aim of the study was to evaluate whether the cephalic phase of insulin release is still present in patients submitted to simultaneous kidney and pancreas transplantation. Subjects were five kidney-pancreas-transplanted patients (group P) and five control (group C). The experimental protocol lasted 30 minutes, and blood samples were collected at 1-minute intervals. After a 20-minute period of steady-state fasting (premeal period), subjects received a palatable standard meal (pizza). Samples were collected over the subsequent 10 minutes (meal period). No evidence of an increase in serum free insulin, serum C-peptide, and plasma glucagon during food ingestion was observed in group P whereas the test was effective in eliciting cephalic-phase insulin and glucagon release in group C. Gastric inhibitory polypeptide and somatostatin did not show any variation during the test in both groups. In conclusion, the absence of cephalic-phase insulin and glucagon release in group P could be explained by denervation of the grafted pancreas. This early alteration could contribute to the impairment in glucose tolerance frequently observed in successfully pancreas-transplanted patients.

Improvement in blunted glucagon response to insulin-induced hypoglycemia by strict glycemic control in diabetics

To elucidate the mechanism of impaired pancreatic A cell function in hypoglycemia in diabetics, the effect of long-term strict glycemic regulations on hypoglycemia-induced glucagon secretion was studied. Firstly, the effect of plasma insulin concentrations on suppressing A cell was studied in healthy volunteers by injecting insulin at doses of 0.1 U/kg and 0.3 U/kg. With 0.3 U/kg of insulin, the rate of fall in glycemia and the nadir of blood glucose were made similar to those with 0.1 U/kg of insulin by glucose infusion with artificial endocrine pancreas. Plasma glucagon response after 0.3 U/kg of insulin was significantly suppressed as compared to that after 0.1 U/kg of insulin, demonstrating that not only hypoglycemic stimulus but also plasma insulin concentration were important determinants responsible for glucagon secretion in insulin-induced hypoglycemia. Secondly, effect of strict glycemic control was studied. Short-acting insulin at a dose of 0.1 U/kg was injected in an intravenous bolus form into 12 insulin-dependent (IDDM) and 9 non-insulin-dependent (NIDDM) diabetics before and 1-3 months after strict glycemic control with multiple insulin injections therapy. Before strict glycemic regulations in IDDM, no significant rise in plasma glucagon concentrations was observed during the insulin-induced hypoglycemia. In NIDDM, a rise in plasma glucagon concentrations was observed, though the response was delayed. After strict glycemic regulations, in patients with residual endogenous insulin secretion, the glucagon response to hypoglycemia improved considerably in IDDM and normalized in NIDDM. In IDDM and NIDDM, improvement in glucagon response to hypoglycemia related positively to daily urinary secretion rate of C-peptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucagon, catecholamine and pancreatic polypeptide secretion in type I diabetic recipients of pancreas allografts

Successful pancreas transplantation in type I diabetic patients restores normal fasting glucose levels and biphasic insulin responses to glucose. However, virtually no data from pancreas recipients are available relative to other islet hormonal responses or hormonal counterregulation of hypoglycemia. Consequently, glucose, glucagon, catecholamine, and pancreatic polypeptide responses to insulin-induced hypoglycemia and to stimulation with arginine and secretin were examined in 38 diabetic pancreas recipients, 54 type I diabetic nonrecipients, and 26 nondiabetic normal control subjects. Glucose recovery after insulin-induced hypoglycemia in pancreas recipients was significantly improved. Basal glucagon levels were significantly higher in recipients compared with nonrecipients and normal subjects. Glucagon responses to insulin-induced hypoglycemia were significantly greater in the pancreas recipients compared with nonrecipients and similar to that observed in control subjects. Glucagon responses to intravenous arginine were significantly greater in pancreas recipients than that observed in both the nonrecipients and normal subjects. No differences were observed in epinephrine responses during insulin-induced hypoglycemia. No differences in pancreatic polypeptide responses to hypoglycemia were observed when comparing the recipient and nonrecipient groups, both of which were less than that observed in the control subjects. Our data demonstrate significant improvement in glucose recovery after hypoglycemia which was associated with improved glucagon secretion in type I diabetic recipients of pancreas transplantation.

Hypoglycemia in diabetes among children and adolescents

Hypoglycemia is one of the most common early complications in insulin-dependent diabetes mellitus (IDDM). Hypoglycemia in children may be considered a risk factor for brain damage and later intellectual impairment, and carries with it a high degree of child and parental anxiety. Recent studies have shown that in IDDM patients, and especially in those on intensive therapy, there is a defect in glucose counter-regulation, increased frequency of hypoglycemic episodes, loss of hypoglycemic awareness and responsiveness. Autonomic neuropathy, glucagon deficiency and low catecholamine response were implied in the pathogenesis of these disorders. In addition, uncontrolled IDDM patients show hypoglycemic symptoms at a higher blood glucose level. These recent observations may suggest that attempts to improve metabolic control may increase the risk of severe hypoglycemia. If so, some alterations in our therapeutic goals must be considered.

Contribution of cortisol to glucose counterregulation in humans

To test the hypothesis that cortisol secretion plays a counterregulatory role in hypoglycemia in humans, four studies were performed in eight normal subjects. In all studies, insulin (15 mU.m-2.min-1) was infused subcutaneously (plasma insulin 27 +/- 1 microU/ml). In study 1, plasma glucose concentration and glucose fluxes [( 3-3H]glucose), substrate, and counterregulatory hormone concentrations were simply monitored, and plasma glucose decreased from 89 +/- 2 to 52 +/- 2 mg/dl for 12 h. In study 2, (pituitary-adrenal-pancreatic clamp), insulin and counterregulatory hormone secretion (except for catecholamines) was prevented by somatostatin (0.5 mg/h, iv) and metyrapone (0.5 g/4 h, per os), and glucagon, cortisol, and growth hormone were infused to reproduce the concentrations of study 1. In study 3 (lack of cortisol increase), the pituitary-adrenal-pancreatic clamp was performed with maintenance of plasma cortisol at basal levels, and glucose was infused, whenever needed, to reproduce plasma glucose concentration of study 2. Study 4 was identical to study 3, but exogenous glucose was not infused. Isolated lack of cortisol increase caused a approximately 22% decrease in hepatic glucose production (P less than 0.01) and a approximately 15% increase in peripheral glucose utilization (P less than 0.01), which resulted in greater hypoglycemia (37 +/- 2 vs. 52 +/- 2 mg/dl, P less than 0.01) despite compensatory increases in plasma epinephrine. Lack of cortisol response also reduced plasma free fatty acid, beta-hydroxybutyrate, and glycerol concentrations approximately 50%. We conclude that cortisol normally plays an important counterregulatory role during hypoglycemia by augmenting glucose production, decreasing glucose utilization, and accelerating lipolysis.

Effects of chronic sodium salicylate feeding on the impaired glucagon and epinephrine responses to insulin-induced hypoglycaemia in streptozotocin diabetic rats

The potential role of endogenous prostaglandins in glucagon and epinephrine responses to insulin-induced hypoglycaemia was studied in streptozotocin-diabetic and age-matched control adult male rats. Rats made diabetic with a single intravenous injection of streptozotocin (65 mg/kg) developed impaired glucagon and epinephrine responses to insulin-induced hypoglycaemia by 80-100 days. Plasma glucagon levels in response to insulin-induced hypoglycaemia in streptozotocin-diabetic rats (167 +/- 67 pg/ml) were significantly lower (p less than 0.01) than those in control rats (929 +/- 272 pg/ml). Similarly, plasma epinephrine levels in hypoglycaemic state in streptozotocin-diabetic rats (11 +/- 8 pmol/ml) were also significantly lower (p less than 0.01) compared to control rats (37 +/- 13 pmol/ml). Streptozotocin-diabetic rats provided with sodium salicylate (25 mg/100 ml) in their drinking water from day one of diabetes exhibited prevention of the blunted glucagon and epinephrine responses to insulin-induced hypoglycaemia. About 80-100 days after the chronic sodium salicylate treatment in streptozotocin-diabetic rats, both plasma glucagon levels (1080 +/- 169 pg/ml) and plasma epinephrine levels (39 +/- 8 pmol/ml) were essentially identical to plasma glucagon levels (1074 +/- 134 pg/ml) and plasma epinephrine levels (37 +/- 5 pmol/ml) in control rats in hypoglycaemic state. These animals also exhibited an improvement in the diabetic state in that they had less severe hyperglycaemia and lack of weight gain. These results suggest that the blunted glucagon and epinephrine responses to insulin-induced hypoglycaemia may be related to altered prostaglandin levels in streptozotocin-diabetes.

Superactive somatostatin analog decreases plasma glucose and glucagon levels in diabetic rats

The action of the new analog of somatostatin, D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2 (RC-160), on plasma glucagon and glucose levels was evaluated in streptozotocin-diabetic rats. The effect of this analog on the insulin-induced hypoglycemia in diabetic rats was also investigated in order to evaluate the risk of exacerbating hypoglycemia. Administration of analog RC-160, in a dose of 25 micrograms/kg b. wt. SC, inhibited plasma glucagon secretion and decreased plasma glucose levels. This effect also occurred when plasma glucagon and glucose levels were first elevated by arginine infusion, 1000 mg/kg/hr for 30 min. Subcutaneous injection of regular insulin, 15 U/kg b. wt., produced hypoglycemia with a progressive increase in glucagon levels. Analog RC-160 completely suppressed the hypoglycemia-induced glucagon release for up to 150 min after injection of the analog or insulin. A greater decrease in the plasma glucose level was observed in the group treated with insulin and the analog than in the group injected only with insulin. These results indicate that somatostatin analog RC-160 can produce a marked and prolonged inhibition of glucagon release and a decrease in the plasma glucose level in diabetic rats. This analog may be useful as an adjunct to insulin in the treatment of diabetic patients, although caution should be exercised, to prevent hypoglycemia when using somatostatin analogs together with insulin.

Responses of peripheral blood cells and lymphocyte subpopulations to insulin-induced hypoglycaemia in human insulin-dependent (Type 1) diabetes

Changes in counts of peripheral blood cells including lymphocytes and lymphocyte subpopulations were examined in response to acute insulin-induced hypoglycaemia in fourteen insulin-dependent diabetic patients of differing duration, and in eight normal subjects. In patients with a short duration of diabetes (less than 5 years) an initial lymphocytosis preceded a later granulocytosis, similar to changes in the normal group following hypoglycaemia. The lymphocytosis comprised increments in T11 (total), T4 (helper), and T8 (suppressor/cytotoxic) lymphocyte subsets, but B lymphocytes did not rise. In diabetic patients of longer duration (greater than 15 years) the initial lymphocytosis was attenuated, the T4 subset response being absent and the T11 subset response was diminished. The lower lymphocyte responses in the long-term diabetics were unrelated to differences in the hormonal responses to hypoglycaemia or to the rate of blood glucose recovery. Rapid mobilization of specific lymphocyte subpopulations appears to be abnormal in long-term insulin-dependent diabetes, and may indicate underlying immunological dysfunction.

Defective glucose counterregulation after strict glycemic control of insulin-dependent diabetes mellitus

We infused small doses of insulin (0.3 mU per kilogram of body weight per minute; range, 0.9 to 1.7 U per hour) for three hours into 8 subjects who did not have diabetes, 11 patients with well-controlled diabetes (hemoglobin A1, 7.6 +/- 0.7 percent), and 10 patients with poorly controlled diabetes (hemoglobin A1, 11.5 +/- 1.7 percent) to simulate the mild peripheral hyperinsulinemia observed during insulin treatment. Normoglycemia was established in the patients during the night before study. During the insulin infusion, the plasma glucose level stabilized at 60 to 70 mg per deciliter (3.3 to 3.9 mmol per liter) in the subjects without diabetes and the patients with poorly controlled diabetes, because of a rebound increase in hepatic glucose production. In contrast, hypoglycemia developed in the patients with well-controlled diabetes (42 +/- 2 mg of glucose per deciliter, or 2.3 +/- 0.1 mmol per liter, P less than 0.01) as glucose production remained suppressed. The hypoglycemia in the patients with well-controlled diabetes was associated with a lowering of the plasma threshold of glucose that triggered a release of epinephrine (less than 45 mg of glucose per deciliter, or 2.5 mmol per liter, vs. greater than 55 mg per deciliter, or 3.1 mmol per liter, in the other groups, P less than 0.01) as well as an enhanced sensitivity to the suppressive effects of insulin on hepatic glucose production. Nearly identical disturbances in glucose counterregulation and decreased perception of hypoglycemia developed when four of the subjects with poorly controlled diabetes were restudied after intensive treatment. We conclude that strict control of diabetes induces physiologic alterations (delayed release of epinephrine and persistent suppression of glucose production) that impair glucose counterregulation to doses of insulin in the therapeutic range. These defects may contribute to the increased incidence of severe hypoglycemia reported during intensive insulin therapy.

Glucose counterregulation during recovery from neuroglucopenia: which mechanism is important?

Neuroglucopenia (NGP), which is a serious potential hazard for all insulin-treated diabetics, stimulates many neural and hormonal responses including increased glucagon secretion and activation of beta-adrenergic receptors of the autonomic nervous system. To determine which of these responses is important in recovery from NGP, we induced NGP in baboons by the intravenous (IV) injection of 2-deoxy-D-glucose with and without beta-adrenergic blockade (propranolol) and somatostatin. Thirty minutes after the induction of NGP the animals recovered, and the mean (+/- SEM) rise in arterial plasma glucose was 6.6 +/- 0.9 mmol/L, in glycerol 0.106 +/- 0.22 mmol/L, and in beta-hydroxybutyrate 0.091 +/- 0.22 mmol/L. Animal recovery and glucose rise were uninfluenced by the infusion of propranolol (mean 30 minute plasma glucose rise of 6.2 +/- 0.8 mmol/L) and somatostatin (6.8 +/- 0.8 mmol/L). However, the combined infusion of somatostatin and propranolol prevented animal recovery and glucose rise (1.0 +/- 0.1 mmol/L). The glycerol and beta-hydroxybutyrate rises were blocked by the propranolol infusion alone. Thus, recovery from NGP and the associated rise in plasma glucose, glycerol, and beta-hydroxybutyrate are prevented by the combination of the suppression of the glucagon and beta-adrenergic response to NGP. Furthermore, if the results of our study are extrapolated to insulin-dependent diabetic patients, most of whom have an impaired glucagon response to insulin-induced hypoglycemia/neuroglucopenia, they would be critically dependent on beta-adrenergic mechanisms for recovery from NGP.

Counterregulatory hormone release after human and porcine insulin in healthy subjects and patients with pituitary disorders

Human and porcine insulin were administered intravenously to a group of healthy volunteers in two different doses (0.075 IU/kg body weight and 0.12 IU/kg body weight) and to two groups of randomly selected patients with pituitary disorders in a dose adapted to their individual glucose tolerance (0.12-0.17 IU/kg body weight for porcine and 0.15-0.18 IU/kg body weight for human insulin). The blood glucose and potassium lowering effect, the feedback regulation of endogenous insulin release, and the liberation of the counterregulatory hormones glucagon, cortisol, adrenocorticotropic hormone (ACTH), prolactin (hPRL), human growth hormone (hGH), and catecholamines were measured before and after injection of human or porcine insulin. The maximal effect, the area under the concentration-time curve, the percentage effect, and the increase above baseline for the two doses of insulin and the two types of insulin were compared. There were no significant differences in the calculated parameters between the two insulin types at the same doses except with prolactin. At 0.075 IU/kg human insulin induced significantly less prolactin release than porcine insulin. Comparing the two doses of the same insulin serum insulin levels, blood glucose, glucagon, norepinephrine, and prolactin were lower at the low dose of each insulin. In addition ACTH and epinephrine were also lower after human insulin at 0.075 IU/kg. The subjective signs of hypoglycemia were less pronounced after human insulin. It is concluded that the biological effects of human insulin are comparable to porcine insulin although prolactin release is significantly reduced after human insulin. If this difference is an indication of different receptor sensitivities for human and porcine insulin in the central nervous system and if the diminished signs of hypoglycemia are a consequence of this, then further studies are required.

Hypoglycemic episodes during continuous subcutaneous insulin infusion: decreased frequency but increased susceptibility

There has been concern regarding the susceptibility of patients on continuous subcutaneous insulin infusion (CSII) to hypoglycemic episodes. This study has examined glycemic control, the frequency of hypoglycemic reactions and the counterregulatory response to an IV insulin infusion fo 2.4 units per hour in five brittle insulin-dependent diabetics before and during CSII. CSII was associated a significant reduction in glycosylated hemoglobin, standard deviation of blood glucose estimations and daily insulin dosage. The frequency of symptomatic hypoglycemic reactions was reduced (mean 14/4 weeks pre CSII, 5/4 weeks post CSII, p less than 0.05). However, after CSII the IV insulin caused a more rapid fall in blood glucose from the physiological to the hypoglycemic range while growth hormone and cortisol responses were both reduced (p less than 0.05) and the deficient glucagon response was not improved. Thus, although the frequency of reported hypoglycemic reactions was reduced by CSII, susceptibility to hypoglycemia due to excess insulin delivery was enhanced, owing to increased insulin sensitivity and/or additional impairment of the counterregulatory response.

Mechanisms of glucagon secretion during insulin-induced hypoglycemia in man. Role of the beta cell and arterial hyperinsulinemia

To elucidate the mechanisms controlling the response of glucagon to hypoglycemia, a vital component of the counterregulatory hormonal response, the role of intraislet insulin was studied in seven normal subjects and five subjects with insulin-dependent diabetes mellitus (IDDM) (of less than 15-mo duration). In the normal subjects, hypoglycemia (arterial plasma glucose [PG] 53 +/- 3 mg/dl) induced by an intravenous insulin infusion (30 mU/m2 X min for 1 h, free immunoreactive insulin [FIRI] 58 +/- 2 microU/ml) elicited a 100% fall in insulin secretion and an integrated rise in glucagon of 7.5 ng/ml per 120 min. When endogenous insulin secretion was suppressed by congruent to 50 or congruent to 85% by a hyperinsulinemic-euglycemic clamp (FIRI 63 +/- 1.5 or 147 +/- 0.3 microU/ml, respectively) before hypoglycemia, the alpha cell responses to hypoglycemia were identical to those of the control study. When the endogenous insulin secretion was stimulated by congruent to 100% (hyperinsulinemic-hyperglycemic clamp, FIRI 145 +/- 1.5 microU/ml, PG 132 +/- 2 mg/dl) before hypoglycemia, the alpha cell responses to the hypoglycemia were also superimposable on those of the control study. Finally, in C-peptide negative diabetic subjects made euglycemic by a continuous overnight intravenous insulin infusion, the alpha cell responses to hypoglycemia were comparable to those of normal subjects despite absent beta cell secretion, and were not affected by antecedent hyperinsulinemia (hyperinsulinemic-euglycemic clamp for 2 h, FIRI 61 +/- 2 microU/ml). These results indicate that the glucagon response to insulin-induced hypoglycemia is independent of the level of both endogenous intraislet and exogenous arterial insulin concentration in normal man, and that this response may be normal in the absence of endogenous insulin secretion, in contrast to earlier reports. Thus, loss of beta cell function is not responsible for alpha cell failure during insulin-induced hypoglycemia in IDDM.

C-peptide measurement: methods and clinical utility

Proinsulin is the single chain precursor of insulin. It consists of insulin, plus a peptide which connects the A and B chains of insulin. This peptide is termed C-peptide. C-peptide an insulin are secreted in equimolar amounts from pancreatic beta-cells, Hence, circulating C-peptide levels provide a measure of beta-cell secretory activity. C-peptide measurements are preferable to insulin measurements because of lack of hepatic extraction, slower metabolic clearance rate, and lack of cross reactivity with antibodies to insulin. This article reviews the methods for determination of C-peptide levels in body fluids, and discusses the applications of C-peptide measurement. These include the investigation of hypoglycemia and the assessment of insulin secretory function in insulin-treated and non-insulin-dependent diabetics. The contribution of C-peptide measurement to the understanding of the interrelationships between insulin secretory function and age, sex, obesity, blood lipids, and blood glucose concentrations will also be evaluated.

Effect of prolonged insulin treatment on blunted plasma catecholamine and glucagon increase during insulin hypoglycemia in streptozotocin diabetic rats

The role of prolonged insulin treatment of diabetic rats on the lack of glucagon and catecholamine increases in response to insulin-hypoglycemia was investigated. Streptozotocin diabetic rats were maintained in a normoglycemic state for a long period by intraperitoneal constant infusion of insulin with the Alzet osmotic minipumps. Hyperglucagonemia observed in diabetic rats was normalized with insulin treatment. However, the blunted response of glucagon during insulin-hypoglycemia was not altered with insulin treatment. On the other hand, in diabetic rats the diminished catecholamine response to insulin-induced hypoglycemia was rendered normal after insulin treatment. The data indicate that the lack of glucagon and catecholamine responses in diabetic rats in response to insulin-hypoglycemia can vary independently. The persistent decreased glucagon response in normoglycemic diabetics could be the cause of their impaired recovery from hypoglycemia.