Effect of hypoglycemia on beta-adrenergic sensitivity in normal and type 1 diabetic subjects

Malglycemia in the critical care setting. Part II: Relative and absolute hypoglycemia

INTRODUCTION

The relationship between critical care mortality and hypoglycemia, both relative (>30% below average preadmission glycemia) and absolute (blood glucose (BG) <70 mg/dL (<10 mmol/L)) requires further definition.

METHODS

We assessed the risk-adjusted relationship between hospital mortality with relative hypoglycemia using the Glycemic Ratio (GR), and with absolute hypoglycemia using BG in a retrospective cohort investigation (n = 4790).

RESULTS

Relative hypoglycemia excursions below GR 0.7 with a of 24-h non-exposure period between excursions in those with HbA1c ≥ 8% were independently associated with mortality (n = 373, OR 2.49, 95% CI 1.54-4.04, p = 0.0002) but not those with HbA1c < 8% (n = 4417, OR 0.98 95% CI 0.89-1.08, p = 0.70). Hours below GR 0.7 (1.0037, 0.9995-1.0080, 0.0846) or minimum GR (0.0896, 0.0030-2.6600, 0.1632) were not independently associated with outcome. Absolute hypoglycemia occurred across the HbA1c spectrum in a U-shaped pattern. There was no difference in mortality associated with exposure to BG < 70 mg/dL for HbA1c ≥ 6.5% vs <6.5% (29.7% vs 24.3%, p = 0.77). Hours below 70 mg/dL demonstrated strongest association with outcome, while minimum BG, and excursions below 70 mg/dL were also independently associated.

CONCLUSIONS

Relative hypoglycemia represented by excursions below GR 0.7 in those with HbA1c ≥ 8% occurred commonly and was independently associated with mortality. Absolute hypoglycemia had similar association with mortality regardless of HbA1c.

Glycaemic control in people with diabetes following acute myocardial infarction

Diabetes is a highly prevalent disease associated with considerable cardiovascular end organ damage and mortality. Despite significant changes to the management of acute myocardial infarction over the last two decades, people with diabetes remain at risk of complications and mortality following a myocardial infarct for a multitude of reasons, including increased coronary atherosclerosis, associated coronary microvascular dysfunction, and diabetic cardiomyopathy. Dysglycaemia causes significant endothelial dysfunction and upregulation of inflammation within the vasculature and epigenetic changes mean that these deleterious effects may persist despite subsequent efforts to tighten glycaemic control. Whilst clinical guidelines advocate for the avoidance of both hyper- and hypoglcyaemia in the peri-infarct period, the evidence base is lacking, and currently there is no consensus on the benefits of glycaemic control beyond this period. Glycaemic variability contributes to the glycaemic milieu and may have prognostic importance following myocardial infarct. The use of continuous glucose monitoring means that glucose trends and parameters can now be captured and interrogated, and its use, along with newer medicines, may provide novel opportunities for intervention after myocardial infarction in people with diabetes.

The growing field of immunometabolism and exercise: Key findings in the last 5 years

This perspective review highlights the impact of physical exercise on immunometabolic responses in the past 5 years. Understanding immunometabolism as a part of immunological research is essential. Furthermore, the roles of both acute and chronic effects of physical exercise on health, aging, and chronic diseases in immunometabolic changes should be elaborated. In immune cells, β2 adrenergic signaling stimulates the preferential mobilization of inflammatory phenotypes, such as CD16⁺ monocytes and CD8⁺ T cells, into the bloodstream after a physical exercise session. The mobilization of immune cells is closely related to the availability of energetic substrates for the cell and mechanisms associated with the uptake and oxidation of fatty acids and glucose. These cells, especially senescent T cells, are mobilized to the peripheral tissues and undergo apoptotic signaling, stimulating the creation of a "vacant space" where new cells will be matured and replaced in the circulation. This results in the upregulation of the expression and secretion of anti-inflammatory cytokines (IL-10 and IL-1ra), leading to increased regulatory immune cells that provide immunoregulatory properties. Thus, we suggest that a significant nutrient available to the cell will favor oxidative metabolism, augment ATP production, and consequently maintain the immune cells in their quiescent state, as well as promote rapid activation function. Therefore, based on the studies discussed in this perspective review, we highlight the importance of performing moderate-intensity continuous and high-intensity intermittent aerobic exercises, due to a higher magnitude of energetic demand and release of anti-inflammatory cytokines (IL-6 and IL-10).

Limited impact of impaired awareness of hypoglycaemia and severe hypoglycaemia on the inflammatory profile of people with type 1 diabetes

AIM

To investigate whether a history of severe hypoglycaemia (SH) or the associated presence of impaired awareness of hypoglycaemia (IAH) is characterized by a pro-inflammatory profile in people with type 1 diabetes.

RESEARCH DESIGN AND METHODS

We measured circulating inflammatory markers and pro- and anti-inflammatory cytokine production after ex vivo stimulation of peripheral blood mononuclear cells (PBMCs) in a well-characterized cohort of individuals with type 1 diabetes (n = 239) and in people without diabetes (n = 56). Data were corrected for confounders by using multivariate linear regression models.

RESULTS

People with type 1 diabetes had higher circulating concentrations of high-sensitivity C-reactive protein (hs-CRP; 0.91 [0.36-2.25] vs. 0.52 [0.20-0.98] pg/mL, P < 0.001 and interleukin-18-binding protein (IL-18BP; 1746 [1304-2112] vs. 1381 [1191-1807] pg/mL; P = 0.001) than those without diabetes. In multivariate analysis, only higher hs-CRP concentrations persisted. Neither circulating immune cells nor ex vivo cytokine levels produced by PBMCs in response to an extensive panel of stimuli differed in groups defined by awareness state or a history of SH, apart from elevated IL-18BP in people with, versus those without, history of SH (1524 [1227-1903] vs. 1913 [1459-2408] pg/mL; P < 0.001).

CONCLUSIONS

IAH or history of SH in people with type 1 diabetes was not associated with altered inflammatory profiles, arguing against chronically elevated inflammatory activity mediating the increased cardiovascular risk associated with hypoglycaemia. The finding of higher circulating concentrations of IL-18BP in individuals with a history of SH requires further investigation.

Expression and Signaling of β-Adrenoceptor Subtypes in the Diabetic Heart

Diabetes is a chronic, endocrine disorder that effects millions of people worldwide. Cardiovascular complications are the major cause of diabetes-related morbidity and mortality. Cardiac β₁- and β₂-adrenoceptor (AR) stimulation mediates positive inotropy and chronotropy, whereas β₃-AR mediates negative inotropic effect. Changes in β-AR responsiveness are thought to be an important factor that contributes to the diabetic cardiac dysfunction. Diabetes related changes in β-AR expression, signaling, and β-AR mediated cardiac function have been studied by several investigators for many years. In the present review, we have screened PubMed database to obtain relevant articles on this topic. Our search has ended up with wide range of different findings about the effect of diabetes on β-AR mediated changes both in molecular and functional level. Considering these inconsistent findings, the effect of diabetes on cardiac β-AR still remains to be clarified.

Hypoglycaemia, cardiovascular disease, and mortality in diabetes: epidemiology, pathogenesis, and management

Hypoglycaemia has long been recognised as a dangerous side-effect of treatment of diabetes with insulin or insulin secretagogues. With its potential to disrupt cerebral function, hypoglycaemia can have a major effect on peoples' lives. Study findings have suggested that hypoglycaemia is associated with an increased risk of cardiovascular events and mortality. Different mechanisms by which hypoglycaemia might provoke cardiovascular events have been identified in experimental studies, and in clinical studies cardiac arrhythmias have been reported to be induced by hypoglycaemia, with one report describing sudden death during a severe episode. Emerging evidence suggests that the association between hypoglycaemia and cardiovascular events and mortality is likely to be multifactorial. The association is probably partly caused by confounding, with hypoglycaemia occurring more frequently in people with comorbidities who are also more likely to die than those without. However, people with type 1 or type 2 diabetes also seem at risk of hypoglycaemia-induced cardiovascular effects. This risk should be recognised by clinicians when agreeing glycaemic goals with patients and choosing appropriate glucose-lowering therapies.

Hypoglycemia

Hypoglycemia remains a common problem for patients with diabetes and is associated with substantial morbidity and mortality. This article summarizes our current knowledge of the epidemiology, pathogenesis, risk factors, and complications of hypoglycemia in patients with diabetes and discusses prevention and treatment strategies.

The effect of antecedent hypoglycaemia on β₂-adrenergic sensitivity in healthy participants with the Arg16Gly polymorphism of the β₂-adrenergic receptor

AIMS/HYPOTHESIS

Homozygosity for glycine at codon 16 (GlyGly) of the β(2)-adrenergic receptor may alter receptor sensitivity upon chronic stimulation and has been implicated in the pathogenesis of hypoglycaemia unawareness. We compared the effect of antecedent hypoglycaemia on β(2)-adrenergic receptor sensitivity between GlyGly participants and those with arginine 16 homozygosity (ArgArg) for the β(2)-adrenergic receptor.

METHODS

We enrolled 16 healthy participants, who were either GlyGly (n = 8) or ArgArg (n = 8). They participated randomly in two 2 day experiments. Day 1 consisted of two 2-h hyperinsulinaemic hypoglycaemic (2.8 mmol/l) or euglycaemic (4.8 mmol/l) glucose clamps. On day 2, we measured the forearm vasodilator response to the β(2)-adrenergic receptor agonist salbutamol and the dose of isoprenaline required to increase the heart rate by 25 bpm (IC(25)).

RESULTS

The vasodilator response to salbutamol tended to be greater after antecedent hypoglycaemia than after euglycaemia (p = 0.078), consistent with increased β(2)-adrenergic receptor sensitivity. This effect was driven by a significant increase in β(2)-adrenergic receptor sensitivity following hypoglycaemia compared with euglycaemia in ArgArg participants (p = 0.019), whereas no such effect was observed in the GlyGly participants. Antecedent hypoglycaemia tended to decrease the IC(25) in ArgArg participants, whereas the reverse occurred in the GlyGly participants (GlyGly vs ArgArg group p = 0.047).

CONCLUSION/INTERPRETATION

Antecedent hypoglycaemia did not affect β(2)-adrenergic receptor sensitivity in healthy GlyGly participants, but increased it in ArgArg participants. If these results also hold for participants with type 1 diabetes, such an increase in β(2)-adrenergic receptor sensitivity may potentially reduce the risk of repeated hypoglycaemia and the subsequent development of hypoglycaemia unawareness in ArgArg diabetic participants.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00160056.

Preserved sensitivity to beta2-adrenergic receptor agonists in patients with type 1 diabetes mellitus and hypoglycemia unawareness

BACKGROUND AND OBJECTIVE

Use of beta(2)-adrenergic receptor agonists has been advocated for the treatment of hypoglycemia unawareness in type 1 diabetes. In vitro, however, hypoglycemia unawareness has been associated with reduced beta(2)-adrenergic sensitivity. Therefore, in vivo sensitivity to beta(2)-adrenergic receptor agonist stimulation was compared between type 1 diabetic patients with and without hypoglycemia unawareness and nondiabetic controls.

METHODS

Ten type 1 diabetic patients with hypoglycemia unawareness, 12 type 1 diabetic patients with intact hypoglycemic awareness, and 11 healthy controls were enrolled. beta(2)-Adrenergic sensitivity was determined by measuring the forearm vasodilator response to intraarterial infusion of salbutamol. Salbutamol was infused in six increasing doses ranging from 0.003 to 1.0 mug(1).min(-1).dl(-1). Forearm blood flow (FBF) was bilaterally measured by venous occlusion plethysmography. Diabetic patients received low-dose insulin before FBF measurements to ensure that experiments were carried out under normoglycemic conditions.

RESULTS

At baseline, FBF was 1.9 +/- 0.3 ml(1).min(-1).dl(-1) in controls, 2.3 +/- 0.4 ml(1).min(-1).dl(-1) in patients with intact awareness, and 1.4 +/- 0.1 ml(1).min(-1).dl(-1) in patients with hypoglycemia unawareness (P = 0.048 vs. aware patients). In response to salbutamol, FBF increased 9.1-fold in controls, 8.0-fold in patients with intact awareness, and 10.7-fold in patients with hypoglycemia unawareness (P = NS). Heart rate increased in all groups due to systemic spillover of salbutamol but appeared blunted, considering a greater fall in mean arterial pressure in patients with hypoglycemia unawareness.

CONCLUSIONS

Sensitivity to beta(2)-adrenergic receptor agonist stimulation is preserved in type 1 diabetic patients with hypoglycemia unawareness.

Antecedent hypoglycemia does not alter increased epinephrine-induced lipolysis in type 1 diabetes mellitus

Type 1 diabetic subjects have decreased epinephrine responses to hypoglycemia that may be counterbalanced by increased beta-adrenergic sensitivity. The goal of this study was to determine whether type 1 diabetic subjects have increased metabolic response to epinephrine and to determine the effect of antecedent hypoglycemia on these responses. Muscular glucose uptake across the forearm (forearm glucose uptake, Fick principle) and lipolysis (free fatty acid and glycerol levels) were studied before and during a 4-hour euglycemic, hyperinsulinemic (40 mU x m(-2) x min(-1)) clamp with epinephrine infusion (0.015 microg x kg(-1) x min(-1)) over 3 hours. Subjects were studied twice, once with antecedent hypoglycemia (2.8 mmol/L for two 2-hour sessions) and once with antecedent euglycemia (5 mmol/L) the day prior. Free fatty acid and glycerol concentrations were higher, and total body glucose utilization and forearm glucose uptake during epinephrine were lower in diabetic than in control subjects (P < .05). Antecedent hypoglycemia had no effect. These results demonstrate that type 1 diabetic subjects have increased lipolysis and decreased glucose utilization in response to epinephrine. These effects are not altered by antecedent hypoglycemia.

Mechanisms of hypoglycemia-associated autonomic failure and its component syndromes in diabetes

Iatrogenic hypoglycemia is a problem for people with diabetes. It causes recurrent morbidity, and sometimes death, as well as a vicious cycle of recurrent hypoglycemia, precluding maintenance of euglycemia over a lifetime of diabetes. Improved therapeutic approaches that will minimize both hypo- and hyperglycemia will be based on insight into the pathophysiology of glucoregulation, specifically glucose counterregulation, in insulin-deficient (type 1 and advanced type 2) diabetes. In such patients, hypoglycemia is the result of the interplay of relative or absolute therapeutic insulin excess and compromised physiological (the syndrome of defective glucose counterregulation) and behavioral (the syndrome of hypoglycemia unawareness) defenses against falling plasma glucose concentrations. The concept of hypoglycemia-associated autonomic failure (HAAF) in diabetes posits that recent antecedent iatrogenic hypoglycemia causes both defective glucose counterregulation (by reducing epinephrine responses to a given level of subsequent hypoglycemia in the setting of absent decrements in insulin and absent increments in glucagon) and hypoglycemia unawareness (by reducing sympathoadrenal and the resulting neurogenic symptom responses to a given level of subsequent hypoglycemia) and thus a vicious cycle of recurrent hypoglycemia. The clinical impact of HAAF is well established in type 1 diabetes; it also affects those with advanced type 2 diabetes. It is now known to be largely reversible, by as little as 2-3 weeks of scrupulous avoidance of hypoglycemia, in most affected patients. However, the mechanisms of HAAF and its component syndromes are largely unknown. Loss of the glucagon secretory response, a key feature of defective glucose counterregulation, is plausibly explained by insulin deficiency, specifically loss of the decrement in intraislet insulin that normally signals glucagon secretion as glucose levels fall. Reduced neurogenic symptoms, a key feature of hypoglycemia unawareness, are largely the result of reduced sympathetic neural responses to falling glucose levels. The mechanism by which hypoglycemia shifts the glycemic thresholds for sympathoadrenal activation to lower plasma glucose concentrations, the key feature of both components of HAAF, is not known. It does not appear to be the result of the release of a systemic mediator (e.g., cortisol, epinephrine) during antecedent hypoglycemia or of increased blood-to-brain glucose transport (although increased transport of alternative fuels is conceivable). It is likely the result of alterations of brain metabolism. Although there is an array of clues, the specific alteration remains to be identified. While the research focus has been largely on the hypothalamus, hypoglycemia is now known to activate widespread brain regions, including the medial prefrontal cortex. The possibility that HAAF could be the result of posthypoglycemic brain glycogen supercompensation has also been raised. Finally, there appear to be diverse causes of HAAF. In addition to recent antecedent hypoglycemia, these include exercise- and sleep-related HAAF. Clearly, a unifying mechanism of HAAF would need to incorporate these causes as well. Pending the prevention and cure of diabetes, critical fundamental, translational, and outcomes research is needed if we are to eliminate hypoglycemia from the lives of people affected by diabetes.

Identification of factors associated with impaired hypoglycaemia awareness in patients with type 1 and type 2 diabetes mellitus

OBJECTIVES

To assess clinical factors associated with impaired hypoglycaemia awareness (HA).

METHODS

Survey of 241 type 1 and type 2 diabetic patients hospitalised in a diabetes department for a diabetes education program. Demographic, diabetes and psychiatric characteristics and subjective hypoglycaemic symptoms were recorded by a self-report questionnaire.

RESULTS

Age and body mass index (BMI) was greater and glycated haemoglobin was lower in diabetic patients reporting impaired HA, however, these latter differences became not significant when age was included as a covariate. There were significantly more current smokers among those with impaired HA and controlling for age accentuated this difference. Current treatment by insulin was not associated with impaired HA. Backward stepwise logistic regression showed that type 2 diabetic patients were twice as likely to have impaired HA than type 1 diabetic patients (OR = 2.195, 95% CI: 1.017-4.734, P = 0.04). Moreover, higher age, current smoking and type 2 diabetes interacted significantly in increasing the likelihood of impaired HA. Among those with impaired HA more patients experienced drowsiness and nervousness and less patients reported tremor during the hypoglycaemic episodes. No other symptoms were associated with impaired HA.

CONCLUSION

Type 2 diabetic patients, whether on insulin or not, and especially if they are of advanced age and if they smoke, are at increased risk of impaired HA.

Differing physiological effects of epinephrine in type 1 diabetes and nondiabetic humans

Acute increases of the key counterregulatory hormone epinephrine can be modified by a number of physiological and pathological conditions in type 1 diabetic patients (T1DM). However, it is undecided whether the physiological effects of epinephrine are also reduced in T1DM. Therefore, the aim of this study was to determine whether target organ (liver, muscle, adipose tissue, pancreas, cardiovascular) responses to epinephrine differ between healthy subjects and T1DM patients. Thirty-four age- and weight-matched T1DM (n = 17) and healthy subjects (n = 17) underwent two randomized, single-blind, 2-h hyperinsulinemic euglycemic clamp studies with (Epi) and without epinephrine infusion. Muscle biopsy was performed at the end of each study. Epinephrine levels during Epi were similar in all groups (4,039 +/- 384 pmol/l). Glucose (5.3 +/- 0.06 mmol/l) and insulin levels (462 +/- 18 pmol/l) were also similar in all groups during the glucose clamps. Glucagon responses to Epi were absent in T1DM and significantly reduced compared with healthy subjects. Endogenous glucose production during the final 30 min was significantly greater during Epi in healthy subjects compared with T1DM (8.4 +/- 1.3 vs. 4.4 +/- 0.6 micromol.kg(-1).min(-1), P = 0.041). Glucose uptake showed almost a twofold greater decrease with Epi in healthy subjects vs. T1DM (Delta31 +/- 2 vs. Delta17 +/- 2 nmol.kg(-1).min(-1), respectively, P = 0.026). Glycerol, beta-hydroxybutyrate, and nonesterified fatty acid (NEFA) all increased significantly more in T1DM compared with healthy subjects. Increases in systolic blood pressure were greater in healthy subjects, but reductions of diastolic blood pressure were greater in T1DM patients with Epi. Reduction of glycogen synthase was significantly greater during epinephrine infusion in T1DM vs. healthy subjects. In summary, despite equivalent epinephrine, insulin, and glucose levels, changes in glucose flux, glucagon, and cardiovascular responses were greater in healthy subjects compared with T1DM. However, T1DM patients had greater lipolytic responses (glycerol and NEFA) during Epi. Thus we conclude that there is a spectrum of significant in vivo physiological differences of epinephrine action at the liver, muscle, adipose tissue, pancreas, and cardiovascular system between T1DM and healthy subjects.

Insulin therapy and hypoglycaemia: the size of the problem

BACKGROUND AND METHODS

Hypoglycaemia is a fact of life for people with diabetes mellitus. Mild, asymptomatic episodes occur once or twice a week in insulin-treated diabetic subjects. Asymptomatic hypoglycaemia, including nocturnal hypoglycaemia, occurs in about 25% of diabetic subjects treated with insulin therapy. Mild hypoglycaemia, if recurrent, induces unawareness of hypoglycaemia and impairs glucose counterregulation, which in turn predisposes to severe hypoglycaemia. Even brief hypoglycaemia can cause profound dysfunction of the brain. Prolonged, severe hypoglycaemia can cause permanent neurological sequels. In addition, it is possible that hypoglycaemia may accelerate the vascular complications of diabetes by increasing platelet aggregation and/or fibrinogen formation. Finally, hypoglycaemia may be fatal. Hypoglycaemia induced by insulin as treatment of type 1 diabetes mellitus (T1 DM) is not the consequence of diabetes, but invariably of the non-physiological replacement of insulin.

RESULTS

A number of studies have demonstrated that by moving from non-physiological to more physiological models of insulin therapy, most of the hypoglycaemia problems may be overcome, the percentage of glycated hemoglobin (A1c) decreased, and the quality of life improved. Interestingly, in T1 DM with hypoglycaemia unawareness, prevention of hypoglycaemia reverses not only unawareness but also improves glucose counterregulation, primarily the responses of adrenaline.

CONCLUSIONS

In order to best prevent hypoglycaemia, insulin should preferably be given as continuous subcutaneous infusion via a minipump (the 'golden standard') or multiple daily insulin administrations with insulin analogues (basal insulin glargine, meal insulin rapid-acting insulin analogues) in T1 DM.

Hypoglycemia-Dependent β2-Adrenoceptor Downregulation: A Contributing Factor to Hypoglycemia Unawareness in Patients with Type-1 Diabetes?

To evaluate the influence of the incidence and unawareness of hypoglycemia on lymphocyte beta2-adrenoceptor densities, we measured beta2-adrenoceptor density using [125I]-iodocyanopindolol and CGP 12177 before and after 1 week of treatment optimization in 33 adults with type-1 diabetes mellitus. Diabetes treatment of all patients was modified to improve their glycemic control. During this week, all patients had to complete a protocol with 7 daily glucose measurements, one of which was at night. The subjective symptoms were evaluated in case of hypoglycemia. A significant correlation between a hypoglycemia incidence below (but not above) the threshold of 2.75 mmol/l (50 mg/dl) and beta2-adrenoceptor densities on lymphocytes was found after the study week (r = -0.72, p < 0.00001). Nine patients suffering from hypoglycemia unawareness had a significantly higher incidence of hypoglycemia (p < 0.002) and lower beta2-adrenoceptor densities on lymphocytes compared to 24 patients who recognized all of their hypoglycemic episodes (p < 0.004). We conclude that downregulation of beta2-adrenoceptor densities on lymphocytes occurs as a result of recurrent hypoglycemia defined as glucose levels of < 2.75 mmol/l. Beta2-adrenoceptor densities are decreased in patients with subjective hypoglycemia unawareness and might contribute to the reduced beta-adrenergic sensitivity in this subgroup of patients.

Antecedent adrenaline attenuates the responsiveness to but not the release of counterregulatory hormones during subsequent hypoglycemia

Hypoglycemia unawareness is thought to be the consequence of recurrent hypoglycemia, yet the underlying mechanism is still incompletely understood. The aim of the present study was to determine the role of antecedent elevated adrenaline in the pathogenesis of hypoglycemia unawareness. Sixteen healthy volunteers (eight of either sex) participated in two experiments, performed in random order and at least 3 wk apart. During the morning, three consecutive doses of 0.04, 0.06, and 0.08 microg.kg(-1).min(-1) of adrenaline or matching placebo (normal saline) were infused for the total duration of 1 h. Three hours later, a hyperinsulinemic (360 pmol.m(-2).min(-1)) two-step hypoglycemic (5.0-3.5-2.5 mmol.liter(-1)) clamp study was performed. During hypoglycemia, hypoglycemic symptoms, counterregulatory hormones, cardiovascular responses, and cognitive function were monitored. Hypoglycemia induced similar responses of autonomic and neuroglycopenic symptoms, counterregulatory hormones, and lengthening in reaction time on the choice reaction time task, irrespective of antecedent infusions. However, prior adrenaline was associated with higher exogenous glucose requirements at hypoglycemic nadir (10.1 +/- 1.3 vs. 7.3 +/- 1.3 micromol.kg(-1).min(-1), P = 0.017), an attenuated hypoglycemia-induced fall in blood pressure (mean arterial pressure, -13 +/- 2 vs. -8 +/- 2 mm Hg, P = 0.006), and preserved cognitive function as assessed by the symbol digit test during hypoglycemia, when compared with prior placebo. We conclude that elevated adrenaline attenuates the responsiveness to, but not the release of counterregulatory hormones during subsequent hypoglycemia. As such, adrenaline's role in the development of hypoglycemia unawareness is limited.

Estrogen blunts neuroendocrine and metabolic responses to hypoglycemia

This study tested the hypothesis that estrogen is the mechanism responsible for the sexual dimorphism present in the neuroendocrine and metabolic responses to hypoglycemia. Postmenopausal women receiving (E2; n = 8) or not receiving (NO E2; n = 9) estrogen replacement were compared with age- and BMI-matched male subjects (n = 8) during a single-step 2-h hyperinsulinemic-hypoglycemic clamp. Plasma insulin (599 +/- 28 pmol/l) and glucose (2.9 +/- 0.03 mmol/l) levels were similar among all groups during the glucose clamp. In response to hypoglycemia, epinephrine (2.8 +/- 0.6 vs. 5.8 +/- 0.8 and 4.4 +/- 0.5 nmol/l), glucagon (57 +/- 8 vs. 77 +/- 8 and 126 +/- 18 ng/l), and endogenous glucose production (2 +/- 2 vs. 10 +/- 2 and 6 +/- 3 micro mol x kg(-1) x min(-1)) were significantly lower in E2 vs. both NO E2 and male subjects (P < 0.05). These reduced counterregulatory responses resulted in significantly greater glucose infusion rates (16 +/- 2 vs. 6 +/- 2 and 6 +/- 3 micro mol x kg(-1) x min(-1); P < 0.01) in E2 vs. both NO E2 and male subjects. Pancreatic polypeptide was significantly lower (P < 0.05) in both the E2 and NO E2 groups compared with the male subjects (136 +/- 20 and 136 +/- 23 vs. 194 +/- 16 pmol/l). Last, glycerol (36 +/- 3 vs. 47 +/- 5 micro mol/l; P < 0.05), lactate (1.4 +/- 0.1 vs. 1.8 +/- 0.2 mmol/l; P < 0.05), and muscle sympathetic nerve activity (19 +/- 4 to 27 +/- 4 vs. 27 +/- 5 to 42 +/- 6 bursts/min; P < 0.05) responses to hypoglycemia were all significantly lower in E2 vs. NO E2 subjects. We conclude that estrogen appears to play a major role in the sexual dimorphism present in counterregulatory responses to hypoglycemia in healthy humans.

Hypoglycemia in diabetes

Iatrogenic hypoglycemia causes recurrent morbidity in most people with type 1 diabetes and many with type 2 diabetes, and it is sometimes fatal. The barrier of hypoglycemia generally precludes maintenance of euglycemia over a lifetime of diabetes and thus precludes full realization of euglycemia's long-term benefits. While the clinical presentation is often characteristic, particularly for the experienced individual with diabetes, the neurogenic and neuroglycopenic symptoms of hypoglycemia are nonspecific and relatively insensitive; therefore, many episodes are not recognized. Hypoglycemia can result from exogenous or endogenous insulin excess alone. However, iatrogenic hypoglycemia is typically the result of the interplay of absolute or relative insulin excess and compromised glucose counterregulation in type 1 and advanced type 2 diabetes. Decrements in insulin, increments in glucagon, and, absent the latter, increments in epinephrine stand high in the hierarchy of redundant glucose counterregulatory factors that normally prevent or rapidly correct hypoglycemia. In insulin-deficient diabetes (exogenous) insulin levels do not decrease as glucose levels fall, and the combination of deficient glucagon and epinephrine responses causes defective glucose counterregulation. Reduced sympathoadrenal responses cause hypoglycemia unawareness. The concept of hypoglycemia-associated autonomic failure in diabetes posits that recent antecedent hypoglycemia causes both defective glucose counterregulation and hypoglycemia unawareness. By shifting glycemic thresholds for the sympathoadrenal (including epinephrine) and the resulting neurogenic responses to lower plasma glucose concentrations, antecedent hypoglycemia leads to a vicious cycle of recurrent hypoglycemia and further impairment of glucose counterregulation. Thus, short-term avoidance of hypoglycemia reverses hypoglycemia unawareness in most affected patients. The clinical approach to minimizing hypoglycemia while improving glycemic control includes 1) addressing the issue, 2) applying the principles of aggressive glycemic therapy, including flexible and individualized drug regimens, and 3) considering the risk factors for iatrogenic hypoglycemia. The latter include factors that result in absolute or relative insulin excess: drug dose, timing, and type; patterns of food ingestion and exercise; interactions with alcohol and other drugs; and altered sensitivity to or clearance of insulin. They also include factors that are clinical surrogates of compromised glucose counterregulation: endogenous insulin deficiency; history of severe hypoglycemia, hypoglycemia unawareness, or both; and aggressive glycemic therapy per se, as evidenced by lower HbA(1c) levels, lower glycemic goals, or both. In a patient with hypoglycemia unawareness (which implies recurrent hypoglycemia) a 2- to 3-week period of scrupulous avoidance of hypoglycemia is advisable. Pending the prevention and cure of diabetes or the development of methods that provide glucose-regulated insulin replacement or secretion, we need to learn to replace insulin in a much more physiological fashion, to prevent, correct, or compensate for compromised glucose counterregulation, or both if we are to achieve near-euglycemia safely in most people with diabetes.

Interactions between hypoglycemia and sleep architecture in children with type 1 diabetes mellitus

OBJECTIVES

To assess the interactions between nocturnal hypoglycemia and sleep in children with type 1 diabetes mellitus (DM).

STUDY DESIGN

Children with DM (n = 15) and 15 matched control children underwent full night polysomnographic recordings. Blood glucose levels were measured in the diabetic children by means of the MiniMed Continuous Glucose Monitoring System. Six of the diabetic children were also studied by peripheral arterial tonometry (an indirect indicator of sympathetic responses).

RESULTS

Five children with DM (33%) had profound nocturnal hypoglycemia, which was associated with increased sleep efficiency, increased slow wave sleep, and increased Delta power in spectral analysis of the electroencephalogram. Hypoglycemic episodes were not associated with sympathetic activation. Rapid decline in glucose levels (>25 mg/dL/hour) but not the absolute degree of hypoglycemia were associated with awakenings from sleep.

CONCLUSIONS

We conclude that sleep may inhibit sympathetic and arousal response to hypoglycemia. Rapid changes in glucose levels, independent of absolute glucose levels, may result in awakening from sleep. Continuous measurement of glucose levels during sleep may add important features in the treatment of children with DM.

Management of canine diabetes

The majority of diabetic dogs appear to have a form of type 1 diabetes analogous to the latent autoimmune diabetes of adults (LADA) in humans. Evidence of acute or chronic pancreatitis occurs in about 40% of diabetic dogs. Blindness caused by cataract formation eventually occurs in the majority of diabetic dogs and is not dependent on glycemic control. Insulin is the mainstay of therapy for diabetic dogs, and a conservative approach to insulin therapy is crucial. Most diabetic dogs require twice-daily dosing with lente or NPH insulin to adequately control their clinical signs. The diet fed should primarily be palatable and nutritionally balanced. Improved glycemic control may be achieved in some dogs if the diet contains increased insoluble fiber.

Effect of acute and antecedent hypoglycemia on sympathetic neural activity and catecholamine responsiveness in normal rats

Adrenergic responsiveness to acute hypoglycemia is impaired after prior episodes of hypoglycemia. Although circulating epinephrine responses are blunted, associated alterations in adrenal sympathetic nerve activity (SNA) have not been reported. We examined adrenal nerve traffic in normal conscious rats exposed to acute insulin-induced hypoglycemia compared with insulin with (clamped) euglycemia. We also examined adrenal SNA and catecholamine responses to insulin-induced hypoglycemia in normal conscious rats after two antecedent episodes of hypoglycemia (days -2 and -1) compared with prior episodes of sham treatment. Acute insulin-induced hypoglycemia increased adrenal sympathetic nerve traffic compared with insulin administration with clamped euglycemia (165 +/- 12 vs. 118 +/- 21 spikes/s [P < 0.05]; or to 138 +/- 8 vs. 114 +/- 10% of baseline [P < 0.05]). In additional experiments, 2 days of antecedent hypoglycemia (days -2 and -1) compared with sham treatment significantly enhanced baseline adrenal SNA measured immediately before subsequent acute hypoglycemia on day 0 (180 +/- 11 vs. 130 +/- 12 spikes/s, respectively; P < 0.005) and during subsequent acute hypoglycemia (229 +/- 17 vs. 171 +/- 16 spikes/s; P < 0.05). However, antecedent hypoglycemia resulted in a nonsignificant reduction in hypoglycemic responsiveness of adrenal SNA when expressed as percent increase over baseline (127 +/- 5% vs. 140 +/- 14% of baseline). Antecedent hypoglycemia, compared with sham treatment, resulted in diminished epinephrine responsiveness to subsequent hypoglycemia. Norepinephrine responses to hypoglycemia were not significantly altered by antecedent hypoglycemia. In summary, prior hypoglycemia in normal rats increased adrenal sympathetic tone, but impaired epinephrine responsiveness to acute hypoglycemia. Hence, these data raise the intriguing possibility that increased sympathetic tone resulting from antecedent hypoglycemia downregulates subsequent epinephrine responsiveness to hypoglycemia. Alternatively, it is possible that the decrease in epinephrine responsiveness after antecedent hypoglycemia could be the result of reduced adrenal sympathetic nerve responsiveness.

Diabetic hypoglycaemia

Hypoglycaemia is a major factor preventing insulin-treated patients from achieving normoglycaemia. This reflects the inadequacy of current insulin treatment, which causes high insulin concentrations in the post-absorptive period. Physiological defences to hypoglycaemia include autonomic activation, which limits the fall in glucose level and causes symptoms, alerting patients to an impending episode. Many patients develop defective responses and hypoglycaemia unawareness after longstanding disease or with tight glycaemic control and are then prone to severe attacks. This may be the result of repeated hypoglycaemic episodes, which by altering cerebral glucose uptake, disturb the mechanisms that activate the central response to hypoglycaemia. Preventing further hypoglycaemia can partially reverse these defects and restore symptomatic awareness. Clinical hypoglycaemia has also been implicated in the 'dead in bed' syndrome and in chronic cognitive impairment. The problem of hypoglycaemia will eventually be solved by better insulin delivery and non-invasive glucose meters, but until then, more focused education may have a more substantial impact.