Hypoglycemic counterregulatory responses differ between men and women with type 1 diabetes

The role of captopril in leukotriene deficient type 1 diabetic mice

T1D can be associated with metabolic disorders and several impaired pathways, including insulin signaling, and development of insulin resistance through the renin-angiotensin system (RAS). The main precursor of RAS is angiotensinogen (Agt) and this system is often linked to autophagy dysregulation. Dysregulated autophagy has been described in T1D and linked to impairments in both glucose metabolism, and leukotrienes (LTs) production. Here, we have investigated the role of RAS and LTs in both muscle and liver from T1D mice, and its effects on insulin and autophagy pathways. We have chemically induced T1D in 129sve and 129sve 5LO-/- mice (lacking LTs) with streptozotocin (STZ). To further inhibit ACE activity, mice were treated with captopril (Cap). In muscle of T1D mice, treatment with Cap increased the expression of RAS (angiotensinogen and angiotensin II receptor), insulin signaling, and autophagy markers, regardless of the genotype. In the liver of T1D mice, the treatment with Cap increased the expression of RAS and insulin signaling markers, mostly when LTs were absent. 5LO-/- T1D mice showed increased insulin sensitivity, and decreased NEFA, after the Cap treatment. Cap treatment impacted both insulin signaling and autophagy pathways at the mRNA levels in muscle and liver, indicating the potential role of ACE inhibition on insulin sensitivity and autophagy in T1D.

Short-term fasting lowers glucagon levels under euglycemic and hypoglycemic conditions in healthy humans

Fasting is associated with increased susceptibility to hypoglycemia in people with type 1 diabetes, thereby making it a significant health risk. To date, the relationship between fasting and insulin-induced hypoglycemia has not been well characterized, so our objective was to determine whether insulin-independent factors, such as counterregulatory hormone responses, are adversely impacted by fasting in healthy control individuals. Counterregulatory responses to insulin-induced hypoglycemia were measured in 12 healthy people during 2 metabolic studies. During one study, participants ate breakfast and lunch, after which they underwent a 2-hour bout of insulin-induced hypoglycemia (FED). During the other study, participants remained fasted prior to hypoglycemia (FAST). As expected, hepatic glycogen concentrations were lower in FAST, and associated with diminished peak glucagon levels and reduced endogenous glucose production (EGP) during hypoglycemia. Accompanying lower EGP in FAST was a reduction in peripheral glucose utilization, and a resultant reduction in the amount of exogenous glucose required to maintain glycemia. These data suggest that whereas a fasting-induced lowering of glucose utilization could potentially delay the onset of insulin-induced hypoglycemia, subsequent reductions in glucagon levels and EGP are likely to encumber recovery from it. As a result of this diminished metabolic flexibility in response to fasting, susceptibility to hypoglycemia could be enhanced in patients with type 1 diabetes under similar conditions.

Pathophysiology and management of hypoglycemia in diabetes

In the century since the discovery of insulin, diabetes has changed from an early death sentence to a manageable chronic disease. This change in longevity and duration of diabetes coupled with significant advances in therapeutic options for patients has fundamentally changed the landscape of diabetes management, particularly in patients with type 1 diabetes mellitus. However, hypoglycemia remains a major barrier to achieving optimal glycemic control. Current understanding of the mechanisms of hypoglycemia has expanded to include not only counter-regulatory hormonal responses but also direct changes in brain glucose, fuel sensing, and utilization, as well as changes in neural networks that modulate behavior, mood, and cognition. Different strategies to prevent and treat hypoglycemia have been developed, including educational strategies, new insulin formulations, delivery devices, novel technologies, and pharmacologic targets. This review article will discuss current literature contributing to our understanding of the myriad of factors that lead to the development of clinically meaningful hypoglycemia and review established and novel therapies for the prevention and treatment of hypoglycemia.

Reproductive Life Span and Severe Hypoglycemia Risk in Postmenopausal Women with Type 2 Diabetes Mellitus

BACKGROUND

Estrogen promotes glucose homeostasis, enhances insulin sensitivity, and maintains counterregulatory responses in recurrent hypoglycemia in women of reproductive age. Postmenopausal women with type 2 diabetes mellitus (T2DM) might be more vulnerable to severe hypoglycemia (SH) events. However, the relationship between reproductive factors and SH occurrence in T2DM remains unelucidated.

METHODS

This study included data on 181,263 women with postmenopausal T2DM who participated in a national health screening program from January 1 to December 31, 2009, obtained using the Korean National Health Insurance System database. Outcome data were obtained until December 31, 2018. Associations between reproductive factors and SH incidence were assessed using Cox proportional hazards models.

RESULTS

During the mean follow-up of 7.9 years, 11,279 (6.22%) postmenopausal women with T2DM experienced SH episodes. A longer reproductive life span (RLS) (≥40 years) was associated with a lower SH risk compared to a shorter RLS (<30 years) (adjusted hazard ratio [HR], 0.74; 95% confidence interval [CI], 0.69 to 0.80; P for trend <0.001) after multivariable adjustment. SH risk decreased with every 5-year increment of RLS (with <30 years as a reference [adjusted HR, 0.91; 95% CI, 0.86 to 0.95; P=0.0001 for 30-34 years], [adjusted HR, 0.80; 95% CI, 0.76 to 0.84; P<0.001 for 35-39 years], [adjusted HR, 0.74; 95% CI, 0.68 to 0.81; P<0.001 for ≥40 years]). The use of hormone replacement therapy (HRT) was associated with a lower SH risk than HRT nonuse.

CONCLUSION

Extended exposure to endogenous ovarian hormone during lifetime may decrease the number of SH events in women with T2DM after menopause.

Effect of hypoglycaemia on measures of myocardial blood flow and myocardial injury in adults with and without type 1 diabetes: A prospective, randomised, open-label, blinded endpoint, cross-over study

AIMS

This study examined the effect of experimentally-induced hypoglycaemia on measures of myocardial blood flow and myocardial injury in adults with, and without, type 1 diabetes.

METHODS

In a prospective, randomised, open-label, blinded, endpoint cross-over study, 17 young adults with type 1 diabetes with no cardiovascular risk factors, and 10 healthy non-diabetic volunteers, underwent hyperinsulinaemic-euglycaemic (blood glucose 4.5-5.5 mmol/L) and hypoglycaemic (2.2-2.5 mmol/L) clamps. Myocardial blood flow was assessed using transthoracic echocardiography Doppler coronary flow reserve (CFR) and myocardial injury using plasma high-sensitivity cardiac troponin I (hs-cTnI) concentration.

RESULTS

During hypoglycaemia, coronary flow reserve trended non-significantly lower in those with type 1 diabetes than in the non-diabetic participants (3.54 ± 0.47 vs. 3.89 ± 0.89). A generalised linear mixed-model analysis examined diabetes status and euglycaemia or hypoglycaemia as factors affecting CFR. No statistically significant difference in CFR was observed for diabetes status (p = .23) or between euglycaemia and hypoglycaemia (p = .31). No changes in hs-cTnI occurred during hypoglycaemia or in the recovery period (p = .86).

CONCLUSIONS

A small change in CFR was not statistically significant in this study, implying hypoglycaemia may require more than coronary vasomotor dysfunction to cause harm. Further larger studies are required to investigate this putative problem.

Evaluation of Hypoglycemia and Associated Factors among Patients with Type 1 Diabetes on Follow-Up Care at St. Paul's Hospital Millennium Medical College, Addis Ababa, Ethiopia

BACKGROUND

Hypoglycemia is one of the most common acute complications of type 1 diabetes mellitus (T1DM). The knowledge of the factors associated with hypoglycemia will help in the prevention and management of the problem. Therefore, this study was conducted to assess hypoglycemia and its associated factors among T1DM patients who attended the diabetes outpatient clinic of St. Paul's Hospital Millennium Medical College (SPHMMC).

METHODS

A cross-sectional study was conducted at the diabetes clinic of SPHMMC. Data on sociodemographic and clinical characteristics including duration of diabetes, type of insulin they have been taking, the factors associated with hypoglycemia, and the severity stage of hypoglycemia was obtained. Data was collected using a structured questionnaire and chart review. Multivariate logistic regression model was used to identify factors associated with hypoglycemia.

RESULT

Out of the 247 participants who were recruited into the study, 233 (94.3%) of them experienced hypoglycemia. A total of 6.9 events of hypoglycemia per patient per year happened. Particularly, the events were categorized as 3.1 mild events, 2.3 moderate events, and 0.93 severe events of hypoglycemia. Shorter duration of diabetes history (<1 year) was significantly associated with less experience of hypoglycemia (AOR = 0.09, 95% CI: 0.01-0.90). However, blood glucose monitoring at home was found to be significantly associated with more report of hypoglycemia (AOR = 5.77, 95% CI: 1.16-28.66).

CONCLUSION

The prevalence of hypoglycemia among T1DM patients was found as substantially high. Self/family blood glucose monitoring at home could not guarantee to minimize the occurrence of hypoglycemia events. Finger stick home blood glucose monitoring should be given a special attention. Therefore, the involvement of health care providers in diabetes care should be encouraged to address the occurrence of hypoglycemia in T1DM patients.

Effect of once-weekly semaglutide on the counterregulatory response to hypoglycaemia in people with type 2 diabetes: A randomized, placebo-controlled, double-blind, crossover trial

AIMS

To investigate the effects of semaglutide vs placebo on glucagon and other counterregulatory hormones during hypoglycaemia in type 2 diabetes (T2D).

METHODS

In this double-blind, placebo-controlled, single-centre trial, we randomized 38 men and women (treated only with metformin) 1:1 to 2 12-week crossover periods of once-weekly subcutaneous semaglutide or placebo, each followed by a hypoglycaemic clamp procedure. The primary endpoint was change in glucagon concentration from target plasma glucose (PG) level 5.5 mmol/L to nadir (target 2.5 mmol/L).

RESULTS

The mean (range) participant age was 54.2 (41-64) years, body mass index 29.4 (23.3-36.1) kg/m² , glycated haemoglobin 60.8 (44.3-83.6) mmol/mol (7.7 [6.2-9.8]%), and diabetes duration 4.5 (0.3-13.2) years. A total of 35 participants completed the trial and were included in the analyses. During the hypoglycaemic clamp from 5.5 mmol/L PG to nadir, the absolute change in mean glucagon concentration was similar for semaglutide vs placebo: 88.3 vs 83.1 pg/mL (estimated difference 5.2 pg/mL [95% confidence interval -7.7 to 18.1]). Concentrations of other counterregulatory hormones increased with both treatments, with a statistically significantly lower increase for noradrenaline and cortisol with semaglutide vs placebo. The glucose infusion rate to maintain constant clamp levels was similar for each treatment group, suggesting an overall similar counterregulatory response. The mean hypoglycaemic symptom score and proportion of participants recognizing hypoglycaemia during the study were lower for semaglutide vs placebo treatment at nadir, but cognitive function test results were similar. No new safety issues were observed for semaglutide.

CONCLUSIONS

Semaglutide treatment did not compromise the counterregulatory glucagon response during experimental hypoglycaemia in people with T2D.

Recurrent Hypoglycemia Exacerbates Cerebral Ischemic Damage in Diabetic Rats via Enhanced Post-Ischemic Mitochondrial Dysfunction

Diabetes significantly increases the risk of stroke and post-stroke mortality. Recurrent hypoglycemia (RH) is common among diabetes patients owing to glucose-lowering therapies. Earlier, we showed that RH in a rat model of insulin-dependent diabetes exacerbates cerebral ischemic damage. Impaired mitochondrial function has been implicated as a central player in the development of cerebral ischemic damage. Hypoglycemia is also known to affect mitochondrial functioning. The present study tested the hypothesis that prior exposure of insulin-treated diabetic (ITD) rats to RH exacerbates brain damage via enhanced post-ischemic mitochondrial dysfunction. In a rat model of streptozotocin-induced diabetes, we evaluated post-ischemic mitochondrial function in RH-exposed ITD rats. Rats were exposed to five episodes of moderate hypoglycemia prior to the induction of cerebral ischemia. We also evaluated the impact of RH, both alone and in combination with cerebral ischemia, on cognitive function using the Barnes circular platform maze test. We observed that RH exposure to ITD rats leads to increased cerebral ischemic damage and decreased mitochondrial complex I activity. Exposure of ITD rats to RH impaired spatial learning and memory. Our results demonstrate that RH exposure to ITD rats potentially increases post-ischemic damage via enhanced post-ischemic mitochondrial dysfunction.

Sex-related differences in fuel utilization and hormonal response to exercise: implications for individuals with type 1 diabetes

Sex-related differences in metabolic and neuroendocrine response to exercise in individuals without diabetes have been well established. Men and women differ in fuel selection during exercise, in which women rely to a greater extent on fat oxidation, whereas males rely mostly on carbohydrate oxidation for energy production. The difference in fuel selection appears to be mediated by sex-related differences in hormonal (including catecholamines, growth hormone, and estrogen) response to different types and intensities of exercise. In general, men exhibit an amplified counter-regulatory response to exercise, with elevated levels of catecholamines compared with women. However, women exhibit greater sensitivity to the lipolytic action of the catecholamines and deplete less of their glycogen stores than men during exercise, which suggests that women may experience a greater defense in blood glucose control after exercise than men. Conversely, little is known about sex-related differences in response to exercise in individuals with type 1 diabetes (T1D). A single study investigating sex-related differences in response to moderate aerobic exercise in individuals with T1D found sex-related differences in catecholamine response and fuel selection, but changes in blood glucose were not measured. To our knowledge, there are no studies investigating sex-related differences in blood glucose responses to different types and intensities of exercise in individuals with T1D. This review summarizes sex-related differences in exercise responses that could potentially impact blood glucose levels during exercise in individuals with T1D and highlights the need for further research.

Could Age, Sex and Physical Fitness Affect Blood Glucose Responses to Exercise in Type 1 Diabetes?

Closed-loop systems for patients with type 1 diabetes are progressing rapidly. Despite these advances, current systems may struggle in dealing with the acute stress of exercise. Algorithms to predict exercise-induced blood glucose changes in current systems are mostly derived from data involving relatively young, fit males. Little is known about the magnitude of confounding variables such as sex, age, and fitness level-underlying, uncontrollable factors that might influence blood glucose control during exercise. Sex-related differences in hormonal responses to physical exercise exist in studies involving individuals without diabetes, and result in altered fuel metabolism during exercise. Increasing age is associated with attenuated catecholamine responses and lower carbohydrate oxidation during activity. Furthermore, higher fitness levels can alter hormonal and fuel selection responses to exercise. Compounding the limited research on these factors in the metabolic response to exercise in type 1 diabetes is a limited understanding of how these variables affect blood glucose levels during different types, timing and intensities of activity in individuals with type 1 diabetes (T1D). Thus, there is currently insufficient information to model a closed-loop system that can predict them accurately and consistently prevent hypoglycemia. Further, studies involving both sexes, along with a range of ages and fitness levels, are needed to create a closed-loop system that will be more precise in regulating blood glucose during exercise in a wide variety of individuals with T1D.

Exaggerated glucagon responses to hypoglycemia in women with polycystic ovary syndrome

CONTEXT

Premenopausal women have blunted counter-regulatory hormone responses (CRR) to hypoglycemia compared to men. Postmenopausal women have CRR similar to men; the premenopausal pattern can be restored by estrogen. However, glucagon and pancreatic polypeptide (PP) responses remain lower in postmenopausal women than in men. Since hyperandrogenemia contributes to the metabolic phenotype of polycystic ovary syndrome (PCOS), we hypothesize that CRR to hypoglycemia especially of glucagon and PP is exaggerated in premenopausal women with PCOS compared to premenopausal control women.

STUDY SUBJECTS AND METHODS

Ten obese women with PCOS and 9 control women of similar ethnicity, age and BMI underwent determination of CRR in response to hypoglycemia during 180-min 60mU/m²/min insulin dose hypoglycemic clamp with isotopic assessment of endogenous glucose production (EGP). To assess CRR to hypoglycemia, glucagon, cortisol, growth hormone (GH), epinephrine, norepinephrine, PP, lactate, free fatty acid (FFA), β-hydroxybutyrate, and glycerol levels were sampled at 15-min intervals throughout the clamp.

MAIN FINDINGS

Incremental glucagon levels were ~3-fold higher during hypoglycemia (P=0.03) in PCOS. Postabsorptive, steady-state and incremental GH, cortisol, epinephrine, norepinephrine, PP, FFA, glycerol and β-hydroxybutyrate did not differ. At target glucose levels of ~52mg/dL, insulin mediated glucose disposal (IMGD) was decreased by ~40% (P=0.02) in PCOS, compared to control women, despite ~20% higher steady-state insulin levels (P=0.03). Neither postabsorptive nor steady-state EGP differed. However, postabsorptive lactate levels were ~50% higher (P=0.02). PCOS status (P=0.04) and IMGD (P=0.02) predicted the differential glucagon response to hypoglycemia in separate regression models, however, neither parameter remained an independent predictor in a combined model.

PRINCIPAL CONCLUSIONS

Glucagon responses were increased in PCOS, whereas other CRR did not differ. Women with PCOS were insulin resistant under hypoglycemic conditions and higher postabsorptive lactate levels in PCOS were consistent with this finding. Insulin resistance may have contributed to exaggerated glucagon response to hypoglycemia in PCOS.

Effect of the GLP-1 Receptor Agonist Lixisenatide on Counterregulatory Responses to Hypoglycemia in Subjects With Insulin-Treated Type 2 Diabetes

OBJECTIVE

Counterregulatory responses are critical to prevent hypoglycemia in subjects with type 2 diabetes. This is particularly important in insulin-treated patients. This study explored the effect of the glucagon-like peptide 1 receptor agonist lixisenatide on the hormonal counterregulatory responses to insulin-induced hypoglycemia when added to basal insulin therapy in subjects with type 2 diabetes.

RESEARCH DESIGN AND METHODS

The study was a single-center, double-blind, randomized, placebo-controlled crossover study involving 18 subjects with type 2 diabetes (11 males) with a mean age of 55 years, diabetes duration of 12 years, HbA1c level of 7.7%, fasting blood glucose (FBG) concentration of 9.7 mmol/L, and a BMI of 33 kg/m(2), who were treated with basal insulin (mean duration 7 years, daily dose 39 units/day) and metformin (mean daily dose 2.1 g). Subjects received treatment with lixisenatide or placebo for 6 weeks in random order, with a 4-week washout period in between. After 6 weeks of treatment, subjects underwent a two-step hyperinsulinemic hypoglycemic clamp at 3.5 and 2.8 mmol/L.

RESULTS

After 6 weeks of treatment, HbA1c and FBG levels were lower after lixisenatide therapy than after placebo therapy. At the hypoglycemic level of 3.5 mmol/L, glucagon and epinephrine levels were significantly lower during lixisenatide treatment than during placebo treatment, whereas at 2.8 mmol/L glucagon and epinephrine levels did not differ between the subjects. Cortisol, pancreatic polypeptide, and norepinephrine levels did not differ significantly between the treatments.

CONCLUSIONS

Glucagon and epinephrine levels are reduced by lixisenatide at a concentration of 3.5 mmol/L, but their counterregulatory responses to deep hypoglycemia at a concentration of 2.8 mmol/L are sustained during treatment with lixisenatide in combination with basal insulin.

Incidence and risk factors for severe and symptomatic hypoglycemia in type 1 diabetes. Results of the HYPOS-1 study

OBJECTIVE

Hypoglycemia is common in type 1 diabetes mellitus (T1DM). We aimed to update the incidence of severe and symptomatic hypoglycemia and investigate several correlated factors.

METHODS

In this multicenter, observational retrospective study, the data of 206 T1DM patients from a sample of 2,229 consecutive patients seen at 18 diabetes clinics were analyzed. Sociodemographic and clinical characteristics, severe hypoglycemia in the past 12 months, and symptomatic hypoglycemia in the past 4 weeks were recorded with a self-report questionnaire and a clinical form during a routine visit. Poisson multivariate models were applied.

RESULTS

A minority of patients accounted for the majority of both severe and symptomatic episodes. The incidence rate (IR) of severe hypoglycemia was 0.49 (0.40-0.60) events/person-years. The incidence rate ratio (IRR) was higher in patients with previous severe hypoglycemia (3.71; 2.28-6.04), neuropathy (4.16; 2.14-8.05), long duration (>20 years, 2.96; 1.60-5.45), and on polypharmacy (1.24; 1.13-1.36), but it was lower when a complication was present. The IR of symptomatic hypoglycemia was 53.3 events/person-years, with an IRR significantly higher among women or patients with better education, or shorter duration or on pumps. The IRR was lower in patients with higher BMI or neuropathy or aged more than 50 years.

CONCLUSIONS

Fewer than 20 % of T1DM patients are free from hypoglycemia, with one in six having experienced at least one severe episode in the last year. The distribution is uneven, with a tendency of episodes to cluster in some patients. Severe and symptomatic episodes have different correlates and reflect different conditions.

Albiglutide does not impair the counter-regulatory hormone response to hypoglycaemia: a randomized, double-blind, placebo-controlled, stepped glucose clamp study in subjects with type 2 diabetes mellitus

AIM

To determine if the glucagon-like peptide-1 (GLP-1) receptor agonist albiglutide, once weekly, impairs counter-regulatory responses during hypoglycaemia.

METHODS

We conducted a randomized, double-blind, parallel, placebo-controlled study in subjects with type 2 diabetes mellitus. A single dose of albiglutide 50 mg (n = 22) or placebo (n = 22) was administered on day 1. Glucose was clamped on day 4 (to coincide with the approximate albiglutide maximum plasma concentration) at 9.0, 5.0, 4.0, 3.3 and 2.8 mmol/l (162, 90, 72, 59.4 and 50.4 mg/dl), with a post-clamp recovery period to 3.9 mmol/l (70 mg/dl). Hormone measurements were made at each plateau and adverse events (AEs) were recorded.

RESULTS

The counter-regulatory hormones glucagon, epinephrine, norepinephrine, growth hormone and cortisol were appropriately suppressed when plasma glucose levels were >4.0 mmol/l (>72 mg/dl), but increased in the albiglutide and placebo groups with glucose levels <3.3 mmol/l (<59.4 mg/dl) in response to hypoglycaemia. The area under the curve geometric mean ratios (albiglutide : placebo), calculated from the clamped plateau of 4.0 mmol/l (72 mg/dl) to the glucose recovery point, were not significantly different for any of the counter-regulatory hormones. When plasma glucose levels were >5.0 mmol/l (>90 mg/dl), albiglutide increased pancreatic β-cell secretion of C-peptide in a glucose-dependent manner to a greater extent than did placebo, and it was suppressed in each group when levels were <4.0 mmol/l (<72 mg/dl). No significant difference between groups was observed in the recovery time to glucose level ≥3.9 mmol/l (≥70 mg/dl). There were no clinically relevant differences in AEs or other safety variables.

CONCLUSIONS

A single 50-mg dose of albiglutide was well tolerated and did not impair the counter-regulatory response to hypoglycaemia. These data provide mechanistic evidence supporting the low intrinsic hypoglycaemic potential of albiglutide.

Sexual Dimorphism in Glucose and Lipid Metabolism during Fasting, Hypoglycemia, and Exercise

Sexually dimorphic physiologic responses occur during fasting, hypoglycemia, and exercise. The areas covered in this mini review include studies that have used isotopic tracer methods and/or euglycemic clamp studies to investigate substrate metabolism during the above common physiologic stress. Women have greater reliance on lipid metabolism during fasting, hypoglycemia, and exercise while men exhibit preference of carbohydrate utilization. Plasma glucose concentrations were shown to be lower, while free fatty acids (FFA) and lipolysis higher in women compared to men after fasting. Hypoglycemia resulted in significantly reduced epinephrine, norepinephrine, glucagon, growth hormone, pancreatic polypeptide, and hepatic glucose production responses in females as compared to males. Sexual dimorphism during exercise was demonstrated by higher glycerol and FFA responses in women compared to men and higher carbohydrate oxidation rate in men. Mechanisms that can increase lipolytic rates in women include higher total fat mass, enhanced lipolytic sensitivity to epinephrine, and increased activation of β adrenergic receptors.

Female rats are relatively more sensitive to reduced lipid versus reduced carbohydrate availability

Objectives:

Because females have blunted counterregulatory responses to hypoglycemia relative to males, we hypothesized that females would have greater sensitivity to changes in lipid availability.

Design and subjects:

To assess this, we examined the feeding response to glucoprivation (2-deoxyglucose; 2DG) and lipoprivation (mercaptoacetate; MA) in age-matched male and female Long-Evans rats.

Results:

Males versus females had significantly greater food intake after 250 mg kg⁻¹ of 2DG, but there were no sex differences with the 750 mg kg⁻¹ dose of 2DG. Glucose responses to 250 mg kg⁻¹ of 2DG were also significantly greater in males versus females. In contrast, females had a significant increase in food intake with all doses of MA versus saline, and had significantly greater food intake compared with males at the lowest and highest doses of MA with a trend towards significance with the intermediate dose. To determine whether estradiol (E2) is the mechanism underlying this sexual dimorphism, ovariectomized females were injected with vehicle or 2 μg of E2 every fourth day to mimic the variations in across the estrous cycle. Ovariectomized females significantly increased feeding and glucose after 250 mg kg⁻¹ of 2DG over intact females and E2 had no effect on these responses. Although the feeding response to 2DG was not different, the glucose response to 2DG was still significantly greater in males versus ovariectomies females. However, ovariectomized females also did not increase food intake after MA, regardless of E2 treatment.

Conclusions:

These data collectively suggest that males are relatively more sensitive to glucose deprivation and females are relatively more sensitive to lipid deprivation. Further, these data rule out a role for cyclic changes in E2 in these sex differences.

Modeling the consistency of hypoglycemic symptoms: high variability in diabetes

BACKGROUND

The aim of the present study was to examine symptoms of hypoglycemia, to develop a method to quantify individual differences in the consistency of symptom reporting, and to investigate which factors affect these differences.

METHODS

Participants recorded their symptoms with every episode of hypoglycemia over a 9-12-month period. A novel logistic-type latent variable model was developed to quantify the consistency of each individual's symptom complex and was used to analyze data from 59 subjects (median age, 57.5 years [range, 22-74 years], 65% male, 77% type 1 diabetes) who had experienced 19 or more hypoglycemic episodes. The association between the calculated consistency parameter and age, sex, type and duration of diabetes, and C-peptide and serum angiotensin converting enzyme concentration was examined using a generalized linear model. Analyses were performed under a Bayesian framework, using Markov chain Monte-Carlo methodology.

RESULTS

Individuals exhibited substantial differences in between-episode consistency of their symptom reports, with only a small number of individuals exhibiting high levels of consistency. Men were more consistent than women. No other factors affected consistency in patients with normal hypoglycemia awareness.

CONCLUSIONS

By using a novel stochastic model as a quantitative tool to compare the consistency of hypoglycemic symptom reporting, much greater intra-individual variability in symptom reporting was identified than has been recognized previously. This is relevant when instructing patients on identification of hypoglycemic symptoms and in interpreting symptomatic responses during experimentally induced hypoglycemia.

Exercise-related hypoglycemia in diabetes mellitus

Current recommendations are that people with Type 1 and Type 2 diabetes mellitus exercise regularly. However, in cases in which insulin or insulin secretagogues are used to manage diabetes, patients have an increased risk of developing hypoglycemia, which is amplified during and after exercise. Repeated episodes of hypoglycemia blunt autonomic nervous system, neuroendocrine and metabolic defenses (counter-regulatory responses) against subsequent episodes of falling blood glucose levels during exercise. Likewise, antecedent exercise blunts counter-regulatory responses to subsequent hypoglycemia. This can lead to a vicious cycle, by which each episode of either exercise or hypoglycemia further blunts counter-regulatory responses. Although contemporary insulin therapies cannot fully mimic physiologic changes in insulin secretion, people with diabetes have several management options to avoid hypoglycemia during and after exercise, including regularly monitoring blood glucose, reducing basal and/or bolus insulin, and consuming supplemental carbohydrates.

Free fatty acids are associated with pulse pressure in women, but not men, with type 1 diabetes mellitus

Cardiovascular disease (CVD) is the leading cause of death in type 1 diabetes mellitus (T1D). Pulse pressure, a measure of arterial stiffness, is elevated in T1D and associated with CVD. Free fatty acids (FFAs), elevated in women and abdominal adiposity, are also elevated in T1D and CVD. We thus examined the association of fasting FFAs with pulse pressure and coronary artery calcification (CAC, a marker of coronary atherosclerotic burden) in an adult population (n = 150) of childhood-onset T1D and whether any such associations varied by abdominal adiposity and sex. Mean age and diabetes duration were 42 and 33 years, respectively, when CAC, visceral abdominal adiposity (VAT), and subcutaneous abdominal adiposity (SAT) were determined by electron beam tomography. Free fatty acids were determined by in vitro colorimetry. Pulse pressure was calculated as systolic blood pressure minus diastolic blood pressure. Free fatty acids were log transformed before analyses, and all analyses were controlled for serum albumin. Free fatty acids were associated with pulse pressure in women (r = 0.24, P = .04), but not in men (r = 0.07, P = .55). An interaction for the prediction of pulse pressure was noted between FFAs and both VAT (P = .03) and SAT (P = .008) in women, but only a marginal interaction with SAT (P = .09) and no interaction for VAT (P = .40) with FFAs were observed in men. In multivariable linear regression analysis allowing for serum albumin, age, height, heart rate, albumin excretion rate, hemoglobin A(1c), high-density lipoprotein cholesterol, hypertension medication use, FFAs, SAT, and the interaction between FFAs and SAT, the interaction between FFAs and SAT remained associated with pulse pressure in women (FFAs, P = .04; interaction term, P = .03), but not men (FFAs, P = .32; interaction term, P = .32). FFAs showed no association with log-transformed CAC. Although FFAs were not associated with CAC in either sex, they were associated with pulse pressure in women and their effect appeared to vary by abdominal adiposity, particularly SAT. This finding might help explain the loss of the sex difference in CVD in T1D.

Diabetes: Hypoglycemia-a new approach to an old problem

Hypoglycemia is the major barrier to good glycemic control in patients with diabetes mellitus. Furthermore, randomized controlled trials have emphasized the grave risks associated with severe hypoglycemia in patients with long-standing type 2 diabetes mellitus, and hypoglycemia has also been recognized as a complication of bariatric surgery. New endocrine society guidelines on adult hypoglycemic disorders are, therefore, extremely pertinent.

Greater systemic lipolysis in women compared with men during moderate-dose infusion of epinephrine and/or norepinephrine

Women have lower circulating catecholamine levels during metabolic perturbations, such as exercise or hypoglycemia, but similar rates of systemic lipolysis. This suggests women may be more sensitive to the lipolytic action of catecholamines, while maintaining similar glucoregulatory effects. The aim of the present study, therefore, was to determine whether women have higher rates of systemic lipolysis compared with men in response to matched peripheral infusion of catecholamines, but similar rates of glucose turnover. Healthy, nonobese women (n = 11) and men (n = 10) were recruited and studied on 3 separate days with the following infusions: epinephrine (Epi), norepinephrine (NE), or the two combined. Tracer infusions of glycerol and glucose were used to determine systemic lipolysis and glucose turnover, respectively. Following basal measurements of substrate kinetics, the catecholamine infusion commenced, and measures of substrate kinetics continued for 60 min. Catecholamine concentrations were similarly elevated in women and men during each infusion: Epi, 182-197 pg/ml and NE, 417-507 pg/ml. There was a significant sex difference in glycerol rate of appearance and rate of disappearance with the catecholamine infusions (P < 0.0001), mainly due to a significantly greater glycerol turnover during the first 30 min of each infusion: glycerol rate of appearance during Epi was only 268 +/- 18 vs. 206 +/- 21 micromol/min in women and men, respectively; during NE, only 173 +/- 13 vs. 153 +/- 17 micromol/min, and during Epi+NE, 303 +/- 24 vs. 257 +/- 21 micromol/min. No sex differences were observed in glucose kinetics under any condition. In conclusion, these data suggest that women are more sensitive to the lipolytic action of catecholamines, but have no difference in their glucoregulatory response. Thus the lower catcholamine levels observed in women vs. men during exercise and other metabolic perturbations may allow women to maintain a similar or greater level of lipid mobilization while minimizing changes in glucose turnover.

Effects of acute insulin-induced hypoglycaemia on psychomotor function: people with type 1 diabetes are less affected than non-diabetic adults

AIMS/HYPOTHESIS

We examined the effects of acute insulin-induced hypoglycaemia on psychomotor function in non-diabetic volunteers and in adults with type 1 diabetes.

METHODS

Non-diabetic adults (n = 20) and adults with type 1 diabetes mellitus (n = 16) each underwent a euglycaemic-hyperinsulinaemic glucose clamp on two separate occasions. Arterialised blood glucose was maintained for 1 h at either 4.5 mmol/l (euglycaemia) or 2.5 mmol/l (hypoglycaemia). During this time participants underwent neuropsychological tests to assess psychomotor function.

RESULTS

During hypoglycaemia the non-diabetic participants showed a significant deterioration in the following: (1) four-choice reaction time (p = 0.008); (2) grooved pegboard (a test of manual dexterity; p = 0.004); (3) hand steadiness (p = 0.003); (4) pursuit rotor (a test of fine motor function, attention and coordination; p = 0.018); and (5) test of total body coordination (p = 0.004). No significant differences were observed between euglycaemia and hypoglycaemia in hand-grip (p = 0.897) and line tracing time (p = 0.480) tests. In type 1 diabetes mellitus patients, only four-choice reaction time (p = 0.023) and pursuit rotor (p = 0.045) were impaired significantly during hypoglycaemia.

CONCLUSIONS/INTERPRETATION

Although acute hypoglycaemia caused significant impairment of several psychomotor functions in non-diabetic adults, a lower magnitude of impairment was observed in those with type 1 diabetes. The mechanism underlying this discrepant effect of hypoglycaemia on psychomotor function remains unknown, but may be related to the difference in sympathoadrenal activation observed between the groups. People with type 1 diabetes may also have had a behavioural advantage of over non-diabetic participants derived from their previous exposure to hypoglycaemia or potentially the disparate results arose from hypoglycaemia-induced cerebral adaptation.

Adaptation of glucokinase gene expression in the rat dorsal vagal complex in a model for recurrent intermediate insulin-induced hypoglycemia: impact of gender

Standard therapeutic management of insulin-dependent diabetes mellitus with intermediate-acting insulin poses a significant risk for iatrogenic hypoglycemia and associated hypoglycemia-associated autonomic failure. Gender differences in preservation of counterregulatory function during recurring hypoglycemia have been documented in the clinical setting. In rats, repeated induction of prolonged hypoglycemia by neutral protamine Hagadorn insulin (NPH) results in diminished neuronal transcriptional activation in several key metabolic loci in male, but not female rat brain, including the hindbrain dorsal vagal complex (DVC). Glucose is committed to glycolytic catabolism by hexokinase-mediated phosphorylation. The low-affinity, high K (m) hexokinase, glucokinase (GCK), monitors intracellular glucose levels in pancreatic beta cells, and is purported to fulfill a similar function in the CNS. GCK is expressed in the rat DVC, where mRNA is localized to neurons that exhibit electrophysiological sensitivity to glucose imbalance. The current study investigated the hypothesis that DVC GCK gene expression acclimates to RIIH in a gender-dependent manner. Quantitative real-time RT-PCR was used to evaluate GCK mRNA levels in microdissected DVC tissue obtained from male and female rats before or after one or serial doses of NPH. Basal DVC GCK transcripts were equal between ovariectomized (OVX) female rats implanted with estradiol benzoate (EB) or oil (O). Tissue mRNA levels were increased following a single NPH injection in both groups, but this response was greater in the presence of estrogen. Basal GCK gene expression was elevated by precedent insulin dosing in both O- and EB-implanted rats; however, transcripts were not modified relative to this adjusted baseline during subsequent NPH treatment in either group of females. While acute NPH treatment did not modify tissue transcript levels in orchidectomized (ORDX) or sham-ORDX rats, precedent NPH dosing increased basal GCK mRNA levels and further enhanced gene expression during ensuring hypoglycemia in sham males. These studies provide novel evidence for gender-dimorphic DVC GCK gene responses to single and serial intermediate-acting insulin administration. Further research is required to determine if and how stimulatory versus inhibitory transcriptional adaptation of this gene profile in male and female rats, respectively, impacts glucose-sensing functions in the DVC, and whether such adjustments may contribute to gender differences in magnitude of precedent hypoglycemic impairment of counterregulation.

Type 1 diabetes: exercise and hypoglycemia

The Diabetes Control and Complications Trial demonstrated that tight control of diabetes management greatly reduces the risk of microvascular complications of diabetes. Unfortunately, tight control of blood glucose can also result in hypoglycemia, especially in patients with type 1 diabetes mellitus (T1DM). It is now widely recognized that antecedent hypoglycemia can blunt neuroendocrine, autonomic nervous system (ANS), and metabolic counterregulatory responses to subsequent hypoglycemia. Thus, blunted counterregulatory defenses against falling plasma glucose levels are a major risk factor for hypoglycemia in people with diabetes. This risk is also complicated by a difference in responses between males and females. Because of the qualitative similarity of neuroendocrine, ANS, and metabolic responses to hypoglycemia and exercise, we developed studies to determine whether neuroendocrine and ANS counterregulatory dysfunction play a role in the pathogenesis of exercise-related hypoglycemia in T1DM. Results from these studies have shown that neuroendocrine (catecholamine and glucagon), ANS (muscle sympathetic nerve activity), and metabolic (lipolysis and glucose kinetics) responses are blunted during exercise after antecedent hypoglycemia, and that there is a sexual dimorphism in responses. Similarly, antecedent episodes of exercise can blunt counterregulatory responses during subsequent hypoglycemia, thereby creating reciprocal feed-forward vicious cycles that increase the risk of hypoglycemia during either stress.

Forearm vasoconstrictor response in uncomplicated type 1 diabetes mellitus

BACKGROUND

According to the 'haemodynamic hypothesis', increased tissue perfusion predisposes to microangiopathy in diabetic patients. We hypothesized that the typical haemodynamic changes underlying the increased tissue perfusion can be explained by a decreased sympathetic nerve activity caused by chronic hyperglycaemia. In this study we investigated sympathetic activity in patients with uncomplicated type 1 diabetes mellitus (DM).

MATERIALS AND METHODS

In 15 DM patients (DM duration 6.3 +/- 3.8 year; HbA1c 7.9 +/- 1.3%) and 16 age- and sex-matched healthy volunteers (Control), sympathetic nervous system activity was measured at rest (baseline) and during sympathoneural stimulation (lower body negative pressure (LBNP)) by means of interstitial and plasma noradrenaline (NA) sampling and power spectral analysis. Muscle sympathetic nerve activity (MSNA) was measured before (baseline) and during a cold pressure test. Forearm blood flow was measured during forearm vascular alpha- and beta-adrenergic receptor blockade.

RESULTS

At baseline, forearm vascular resistance (FVR), plasma NA concentrations, MSNA and heart rate variability were similar in both groups. LBNP-induced vasoconstriction was significantly attenuated in the DM group compared with the Control group (DeltaFVR: 12 +/- 4 vs. 19 +/- 3 arbitrary units, P < 0.05). The responses of plasma NA and heart rate variability did not differ.

CONCLUSIONS

Baseline FVR and sympathetic nerve activity are normal in patients with uncomplicated type 1 diabetes. However, the forearm vasoconstrictor response to sympathetic stimulation is attenuated, which cannot be attributed to an impaired sympathetic responsiveness.

Hormonal, subjective, and neurocognitive responses to brief hypoglycemia in postmenopausal women and age-matched men with type 2 diabetes mellitus

Sexual dimorphisms in hypoglycemic counterregulation are well documented in young healthy and type 1 diabetic subjects. Here, we questioned whether sex differences in counterregulation are present also in type 2 diabetic patients who are in a postmenopausal state. In an attempt to answer this question, we examined hormonal responses to a single-step hypoglycemic clamp (50 mg/dL) in 15 postmenopausal women and 15 age-matched men. Patients were also matched for body mass index, HbA(1c), diabetes duration, and diabetes therapy. In addition to hormonal counterregulation, perception of symptoms as well as aspects of neurocognitive function (short-term memory of words and reaction time on an auditory vigilance task) was assessed at baseline and during the hypoglycemic clamp. Hypoglycemia induced a profound rise in almost all counterregulatory hormones, that is, epinephrine, norepinephrine, corticotropin, cortisol, and growth hormone (all P < .007), except for glucagon, which slightly decreased (P = .014). However, none of the responses differed between sexes (all P > .256). In addition, perceived symptoms (P < .001) as well as reaction time on the vigilance task (P < .001) increased, and short-term memory performance tended to deteriorate (P = .091) during hypoglycemia. Again these changes did not differ between the sexes (all P > .370). In sum, data suggest that, in contrast to previous observations in young, healthy, and type 1 diabetic subjects, sex does not represent an important determinant of hormonal, subjective, and neurocognitive responses to hypoglycemia in postmenopausal type 2 diabetic patients. However, the women in our study were all postmenopausal and not receiving hormone replacement therapy. Therefore, our results cannot be generalized to female patients with type 2 diabetes who are premenopausal or on hormone replacement therapy, that is, conditions characterized by increased blood estrogen levels.

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.

Effect of Sex on the Cardiovascular Response to Adrenaline in Humans

Cardiovascular responsiveness to stress conditions differs between men and women. It is not known to what extent this observation is explained by differences in the release of stress hormones like adrenaline, or by differences in the response to adrenaline. Therefore, we quantified the hemodynamic response to infusion of adrenaline (0.04, 0.06, and 0.08 microg x kg(-1) x min(-1) for 20 minutes each) in 8 healthy men and 8 healthy premenopausal women. Arterial plasma adrenaline levels were measured before and after infusion. Heart rate and intra-arterial blood pressure were monitored throughout the experiment. Arterial plasma adrenaline levels increased similarly in both sexes. There was a larger increase in systolic blood pressure in women compared with men (17.6 +/- 2.8 versus 5.1 +/- 3.1 mm Hg, P < 0.01). In contrast, men showed a larger increase in heart rate compared with women (20.3 +/- 1.4 versus 11.2 +/- 2.8 bpm, P < 0.01). In conclusion, these data suggest that the cardiovascular response to adrenaline is predominantly alpha-adrenergic in premenopausal women, and predominantly beta-adrenergic in age-matched men.

Frequency, severity, and morbidity of hypoglycemia occurring in the workplace in people with insulin-treated diabetes

OBJECTIVE

Hypoglycemia was examined in regularly employed people with insulin-treated diabetes to ascertain the frequency and consequences of this problem in the workplace.

RESEARCH DESIGN AND METHODS

A prospective 12-month survey of 243 employed people (age range 20-69 years) with insulin-treated diabetes was performed to record the frequency, severity, and morbidity of hypoglycemia occurring at work. Details of hypoglycemic episodes included time of day, place, activity, causation, blood glucose, treatment, and morbidity. Serial HbA(1c) measurements were recorded.

RESULTS

A total of 1,955 mild (self-treated) episodes of hypoglycemia (8 per person per annum) and 238 severe (requiring external help) episodes (0.98 per person per annum) were recorded. Of the severe hypoglycemic episodes, 148 (62%) occurred at home, 35 (15%) occurred at work in 27 (11%) people (0.14 episodes per person per annum), and 54 (23%) occurred elsewhere; 52% of severe episodes occurred during sleep. Of the severe hypoglycemic episodes reported, adverse events were described in 54 (23%), with 29 losing consciousness (14%), 21 having a seizure (9%), 4 (2%) sustaining a head injury, 5 (2%) suffering another injury, 3 (1%) injuring someone else, and 2 (1%) damaging property. Severe hypoglycemia in the workplace was associated with six episodes of minor soft-tissue injuries.

CONCLUSIONS

In this cohort, severe hypoglycemia in the workplace was uncommon and seldom caused disruption or serious morbidity. On the basis of the frequency and severity of hypoglycemia observed in the present study, restriction of employment opportunities for most people with insulin-treated diabetes may be difficult to justify.

Differential adaptation of neurocognitive brain functions to recurrent hypoglycemia in healthy men

Antecedent hypoglycemia is known to attenuate hormonal and symptomatic responses to subsequent hypoglycemia. Whether this pertains also to hypoglycemia-induced cognitive dysfunction is controversially discussed. Neurocognitive adaptation might essentially depend on the type of function. Here, we compared the influence of recurrent hypoglycemia in 15 healthy men on counterregulatory hormones, subjective symptoms of hypoglycemia, short-term memory performance (word recall), and performance on an auditory attention task (oddball). The attention task was also used to record event-related brain potential (ERP) indicators of stimulus processing. In each subject, three consecutive hypoglycemic clamps were performed, two on day 1 and the third on day 2. Neurocognitive testing was performed during baseline and at two different hypoglycemic plateaus (2.8 and 2.5 mmol/l) during the first and last clamp. As expected, hormonal responses were significantly reduced to the last as compared to the first hypoglycemia indicating adaptation. Subjective symptoms also decreased in response to recurrent hypoglycemia. Short-term memory performance deteriorated distinctly on the first hypoglycemic clamp, but maintained the normal level on the last clamp (P=0.006). Likewise, the impairment in reaction time (P=0.022) and response accuracy (P=0.005) was distinctly smaller on the last than first hypoglycemia. In parallel, the hypoglycemia-induced decrease in P3 amplitude (P=0.019) and the increase in P3 latency (P=0.049) were diminished with recurrent hypoglycemia, indicating that late stages of controlled stimulus processing likewise adapted. In contrast, the distinct decrease in amplitudes of the N1 and P2 components of the ERP (preceding the P3) was closely comparable in response to the first and last hypoglycemia (P>0.3). Together results indicate an adaptation to recurrent hypoglycemia for signs of controlled stimulus processing presumably involving hippocampo-prefrontocortical circuitry, while earlier automatic stages of processing appear to be spared.

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.

Effects of low and moderate antecedent exercise on counterregulatory responses to subsequent hypoglycemia in type 1 diabetes

Antecedent moderate-intensity exercise has been shown to blunt autonomic, neuroendocrine, and metabolic counterregulatory responses to subsequent hypoglycemia in nondiabetic individuals. The aims of the current study were to determine 1) whether this occurs in type 1 diabetic patients and 2) whether the degree of blunting is dependent on exercise intensity. Twenty-seven type 1 diabetic patients (13 women and 14 men) were studied during a single-step, 2-h hyperinsulinemic (9 pmol x kg(-1) x min(-1))-hypoglycemic (approximately 2.8 mmol/l) clamp 1 day after two 90-min exercise bouts at 30% (n = 11) or at 50% (n = 11) Vo(2max) or after no prior stress (control subjects, n = 25). After prior exercise at both 30 and 50% Vo(2max), epinephrine (1,959 +/- 553 and 1,528 +/- 424 vs. 3,420 +/- 424 pmol/l, respectively; P < 0.05) and pancreatic polypeptide (97 +/- 32 and 98 +/- 8 vs. 223 +/- 32 pmol/l, respectively; P < 0.05) responses to subsequent hypoglycemia were significantly lower compared with those of control subjects. Endogenous glucose production was significantly lower, while glucose utilization and, consequently, the exogenous glucose infusion rate needed to maintain hypoglycemia were significantly greater after both exercise intensities compared with that of control subjects. Muscle sympathetic nerve activity was significantly reduced by prior exercise of both intensities at baseline (16 +/- 4 and 22 +/- 4 vs. 31 +/- 3 bursts/min) and during hypoglycemia (22 +/- 4 and 27 +/- 5 vs. 41 +/- 3 bursts/min) compared with that of control subjects (P < 0.05). Total hypoglycemic symptoms were also significantly lower (P < 0.05) in both exercise groups compared with the control group. In summary, repeated episodes of prolonged exercise of both low and moderate intensities blunted key autonomic (epinephrine and pancreatic polypeptide) and metabolic (endogenous glucose production and peripheral glucose uptake) counterregulatory responses to next-day hypoglycemia in type 1 diabetes.

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.

Effects of dexamethasone on the metabolic responses to mental stress in humans

The haemodynamic effects of the sympathetic nervous system (SNS) activations elicited by hypoglycaemia, acute alcohol administration, or insulin can be prevented by a pretreatment with dexamethasone in humans. This suggests a possible role of central corticotropin releasing hormone (GRIT) release. Mental stress activates the SNS, and decreases systemic vascular resistances though a beta-adrenergic-mediated vasodilation thought to involve vascular nitric oxide release. It also increases insulin-mediated glucose disposal, an effect presumably related to vasodilation. In order to evaluate whether activation of SNS by mental stress is glucocorticoid-sensitive, we monitored the haemodynamic and metabolic effects of mental stress during hyperinsulinaemia in healthy humans with and without a 2-day treatment with 8 mg day(-1) dexamethasone. Mental stress decreased systemic vascular resistances by 21.9% and increased insulin-mediated glucose disposal by 2 8.4% without dexamethasone pretreatment. After 2 days of dexamethasone treatment, whole body insulin-mediated glucose disposal was decreased by 40.8%. The haemodynainic effects of mental stress were however, not affected. Mental stress acutely increased insulin-mediated glucose disposal by 28.0%. This indicates that mental stress elicits a stimulation of SNS through dexamethasone-insensitive pathway, distinct of those activated by insulin, alcohol, or hyperglycaemia.

Maternal hypoglycemia during pregnancy in type 1 diabetes: maternal and fetal consequences

There is strong evidence that the avoidance of hyperglycemia is essential inoptimizing pregnancy outcome in type 1 diabetes. The price to pay is a striking increase in severe hypoglycemia (SH), defined as episodes requiring help from another person. During type 1 diabetic pregnancy, occurrence rates of SH up to 15 times higher as in the intensively treated group of the Diabetes Control and Complications Trial (DCCT) are reported. Blood glucose (BG) treatment targets differ considerably between clinics; some authors advocate lower limits as low as 3.3 mmol/l. Improved glycemic control and/or recurrent hypoglycemia (i.e. BG <3.9 mmol/l) may result in impairment of glucose counterregulatory responses. Also, glucose counterregulation may be altered by pregnancy itself. Short-acting insulin analogs may help reduce hypoglycemia with preservation of good glycemic control, but their use during pregnancy has yet to be proven safe.Several clinical studies did not establish an association between maternal hypoglycemia and diabetic embryopathy. However, animal studies clearly indicate that hypoglycemia is potentially teratogenic during organogenesis. Increased rates of macrosomia continue to be observed despite near normal HbA(1c) levels. This may, at least in part, be the result of rebound hyperglycemia elicited by hypoglycemia. Exposure to hypoglycemia in utero may have long-term effects on offspring including neuropsychological defects. It is yet unclear to what extent the benefits of tight glycemic control balance with the increased risk of (severe) hypoglycemia during type 1 diabetic pregnancy. Efforts must be made to avoid low BG, i.e. <3.9 mmol/l, when tightening glycemic control.

Effects of antecedent hypoglycemia, hyperinsulinemia, and excess corticosterone on hypoglycemic counterregulation

This study aimed to differentiate the effects of repeated antecedent hypoglycemia, antecedent marked hyperinsulinemia, and antecedent increases in corticosterone on counterregulation to subsequent hypoglycemia in normal rats. Specifically, we examined whether exposure to hyperinsulinemia or elevated corticosterone per se could impair subsequent counterregulation. Four groups of male Sprague-Dawley rats were used: 1) normal controls (N) had 4 days of sham antecedent treatment; 2) an antecedent hypoglycemia group (AH) had 7 episodes of hyperinsulinemic hypoglycemia over 4 days; 3) an antecedent hyperinsulinemia group (AE) had 7 episodes of hyperinsulinemic euglycemia; and 4) an antecedent corticosterone group (AC) had 7 episodes of intravenous corticosterone to simulate the hypoglycemic corticosterone levels in AH rats. On day 5, hyperinsulinemic euglycemic-hypoglycemic clamps were performed. Epinephrine responses to hypoglycemia were impaired (P < 0.05 vs. N) after antecedent hypoglycemia and hyperinsulinemia. This correlated with diminished (P < 0.05 vs. N) absolute glucose production responses in AH rats and diminished incremental glucose production responses in AE rats. Paradoxically, norepinephrine responses were increased (P < 0.05 vs. N) after antecedent hypoglycemia. Glucagon and corticosterone responses were unaffected by antecedent hypoglycemia and hyperinsulinemia. In AC rats, incremental but not absolute glucose production responses were decreased (P < 0.05 vs. N). However, neuroendocrine counterregulation was unaltered. We conclude that both antecedent hypoglycemia and hyperinsulinemia impair epinephrine and glucose production responses to subsequent hypoglycemia, suggesting that severe recurrent hyperinsulinemia may contribute to the development of hypoglycemia-associated autonomic failure.

Abnormal glucose handling by the kidney in response to hypoglycemia in type 1 diabetes

The frequent occurrence of hypoglycemia in people with type 1 diabetes is attributed to abnormalities in the blood glucose counterregulatory response. In view of recent findings indicating that the kidney contributes to prevent and correct hypoglycemia in healthy subjects, we decided to investigate the role of renal glucose handling in hypoglycemia in type 1 diabetes. Twelve type 1 diabetic patients and 14 age-matched normal individuals were randomized to hyperinsulinemic-euglycemic (n = 6 diabetic subjects and n = 8 control subjects) or hypoglycemic (n = 6 each) clamps with blood glucose maintained either stable near 100 mg/dl (5.6 mmol/l) or reduced to 54 mg/dl (3.0 mmol/l). All study subjects had their renal vein catheterized under fluoroscopy, and net renal glucose balance and renal glucose production and utilization rates were measured using a combination of arteriovenous concentration difference with stable isotope dilution technique. Blood glucose and insulin were comparable in both groups in all studies. In patients with diabetes, elevations in plasma glucagon, epinephrine, and norepinephrine were blunted, and both the compensatory rise in endogenous glucose production and in the net glucose output by the kidney seen in normal subjects with equivalent hypoglycemia were absent. Renal glucose balance switched from a mean +/- SE baseline net uptake of 0.6 +/- 0.4 to a net output of 4.5 +/- 1.3 micromol x kg(-1) x min(-1) in normal subjects, but in patients with diabetes there was no net renal contribution to blood glucose during similar hypoglycemia (mean +/- SE net glucose uptake [baseline 0.7 +/- 0.4] remained at 0.4 +/- 0.3 micromol x kg(-1) x min(-1) in the final 40 min of hypoglycemia; P < 0.01 between groups). We conclude that adrenergic stimulation of glucose output by the kidney, which represents an additional defense mechanism against hypoglycemia in normal subjects, is impaired in patients with type 1 diabetes and contributes to defective glucose counterregulation.

Gender-related differences in counterregulatory responses to antecedent hypoglycemia in normal humans

Compared to men, inherent counterregulatory responses are reduced in healthy and type 1 diabetic women. Despite this, the prevalence of hypoglycemia in patients with type 1 diabetes (type 1 DM) is gender neutral. The aim of this study was to determine the in vivo mechanism(s) responsible for this apparent clinical paradox. The central importance of antecedent hypoglycemia in causing subsequent counterregulatory failure is now established. We, therefore, hypothesized that a gender-related difference to the blunting effects of prior hypoglycemia may exist, and this could explain why type 1 DM women do not have an increased prevalence of hypoglycemia despite reduced counterregulatory responses. Fifteen healthy male and female individuals (eight men and seven women) underwent four separate 2-day experimental protocols in a randomized fashion. Day 1 involved identical morning and afternoon 2-h hyperinsulinemic (9 pmol/kg x min) glucose clamp studies with 5.1 +/- 0.1, 3.9 +/- 0.1, 3.3 +/- 0.1, or 2.9 +/- 0.1 mmol/L. Day 2 consisted of a single 2-h hypoglycemic clamp of 2.9 +/- 0.1 mmol/L. Insulin levels were similar on both days of each protocol in men and women. After day 1 euglycemia (5.1 +/- 0.1 mmol/L), day 2 counterregulatory responses were significantly increased (P < 0.01) in men relative to women. In women, counterregulatory responses were resistant to the effects of day 1 hypoglycemia. Antecedent hypoglycemia of 3.9, 3.3, and 2.9 +/- 0.1 mmol/L produced 3 +/- 2%, 5 +/- 2%, and 25 +/- 4% aggregate reductions in day 2 neuroendocrine, muscle sympathetic nerve activity, and metabolic counterregulatory responses. In marked contrast, identical day 1 hypoglycemia of 3.9, 3.3, and 2.9 +/- 0.1 mmol/L in men produced significantly greater reductions in day 2 counterregulatory responses of 30 +/- 6%, 39 +/- 6%, and 52 +/- 6%, respectively. The net effect of the differential gender effects of antecedent hypoglycemia was to overcome the usually increased (50%) sympathetic nervous system (SNS) counterregulatory responses to hypoglycemia found in men. We conclude that 1) antecedent hypoglycemia produces less blunting of counterregulatory responses to subsequent hypoglycemia in women relative to men; 2) two episodes of antecedent hypoglycemia can overcome the greater SNS response to hypoglycemia usually found in men; and 3) the reduced susceptibility of women to the blunting effects of antecedent hypoglycemia may be the mechanism explaining why, despite inherently reduced SNS counterregulatory responses, female type 1 DM patients have a similar prevalence of hypoglycemia compared to men.