OBJECTIVERecent large randomized trials have linked adverse cardiovascular and cerebrovascular events with hypoglycemia. However, the integrated physiological and vascular biological mechanisms occurring during hypoglycemia have not been extensively examined. Therefore, the aim of this study was to determine whether 2 h of moderate clamped hypoglycemia could decrease fibrinolytic balance and activate pro-atherothrombotic mechanisms in individuals with type 1 diabetes and healthy individuals.RESEARCH DESIGN AND METHODSThirty-five healthy volunteers (19 male and 16 female subjects age 32 ± 2 years, BMI 26 ± 2 kg/m2, A1C 5.1 ± 0.1%) and twenty-four with type 1 diabetes (12 male and 12 female subjects age 33 ± 3 years, BMI 24 ± 2 kg/m2, A1C 7.7 ± 0.2%) were studied during either a 2-h hyperinsulinemic (9 pmol · kg−1 · min−1) euglycemic or hypoglycemic (2.9 ± 0.1 mmol/l) clamp or both protocols. Plasma glucose levels were normalized overnight in type 1 diabetic subjects prior to each study.RESULTSInsulin levels were similar (602 ± 44 pmol/l) in all four protocols. Glycemia was equivalent in both euglycemic protocols (5.2 ± 0.1 mmol/l), and the level of hypoglycemia was also equivalent in both type 1 diabetic subjects and healthy control subjects (2.9 ± 0.1 mmol/l). Using repeated ANOVA, it was determined that plasminogen activator inhibitor (PAI-1), vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM), E-selectin, P-selectin, interleukin-6 (IL-6), vascular endothelial growth factor (VEGF), and adiponectin responses were all significantly increased (P < 0.05) during the 2 h of hyperinsulinemic hypoglycemia as compared with euglycemia in healthy control subjects. All measures except PAI-1 were also found to be increased during hypoglycemia compared with euglycemia in type 1 diabetes.CONCLUSIONSIn summary, moderate hypoglycemia acutely increases circulating levels of PAI-1, VEGF, vascular adhesion molecules (VCAM, ICAM, E-selectin), IL-6, and markers of platelet activation (P-selectin) in individuals with type 1 diabetes and healthy individuals. We conclude that acute hypoglycemia can result in complex vascular effects including activation of prothrombotic, proinflammatory, and pro-atherogenic mechanisms in individuals with type 1 diabetes and healthy individuals.

In the present study the hypothesis tested was that prior exercise may blunt counterregulatory responses to subsequent hypoglycemia. Healthy subjects [15 females (f)/15 males (m), age 27 +/- 1 yr, body mass index 22 +/- 1 kg/m(2), hemoglobin A(Ic) 5.6 +/- 0.5%] were studied during 2-day experiments. Day 1 involved either 90-min morning and afternoon cycle exercise at 50% maximal O2 uptake (VO2(max)) (priorEXE, n = 16, 8 m/8 f) or equivalent rest periods (priorREST, n = 14, 7 m/7 f). Day 2 consisted of a 2-h hypoglycemic clamp in all subjects. Endogenous glucose production (EGP) was measured using [3-3H]glucose. Muscle sympathetic nerve activity (MSNA) was measured using microneurography. Day 2 insulin (87 +/- 6 microU/ml) and plasma glucose levels (54 +/- 2 mg/dl) were equivalent after priorEXE and priorREST. Significant blunting (P < 0.01) of day 2 norepinephrine (-30 +/- 4%), epinephrine (-37 +/- 6%), glucagon (-60 +/- 4%), growth hormone (-61 +/- 5%), pancreatic polypeptide (-47 +/- 4%), and MSNA (-90 +/- 8%) responses to hypoglycemia occurred after priorEXE vs. priorREST. EGP during day 2 hypoglycemia was also suppressed significantly (P < 0.01) after priorEXE compared with priorREST. In summary, two bouts of exercise (90 min at 50% VO2(max)) significantly reduced glucagon, catecholamines, growth hormone, pancreatic polypeptide, and EGP responses to subsequent hypoglycemia. We conclude that, in normal humans, antecedent prolonged moderate exercise blunts neuroendocrine and metabolic counterregulatory responses to subsequent hypoglycemia.

Exercise-related hypoglycemia is common in intensively treated patients with type 1 diabetes. The underlying mechanisms are not clearly defined. In nondiabetic subjects, hypoglycemia blunts counterregulatory responses to subsequent exercise. It is unknown whether this also occurs in type 1 diabetes. Therefore, the goal of this study was to test the hypothesis that prior hypoglycemia could result in acute counterregulatory failure during subsequent exercise in type 1 diabetes. A total of 16 type 1 diabetic patients (8 men and 8 women, HbA 1c 7.8 ؎ 0.3%) were investigated during 90 min of euglycemic cycling exercise, following either two 2-h periods of previous-day hypoglycemia (2.9 mmol/l) or previous-day euglycemia. Patients' counterregulatory responses (circulating levels of counterregulatory hormones, intermediary metabolites, substrate flux via indirect calorimetry, tracer-determined glucose kinetics, and cardiovascular measurements) were comprehensively assessed during exercise. Identical euglycemia and basal insulin levels were successfully maintained during all exercise studies, regardless of blood glucose levels during the previous day. After resting euglycemia, patients displayed normal counterregulatory responses to exercise. Conversely, when identical exercise was repeated after hypoglycemia, the glucagon response to exercise was abolished, and the epinephrine, norepinephrine, cortisol, endogenous glucose production, and lipolytic responses were reduced by 40 -80%. This resulted in a threefold increase in the amount of exogenous glucose needed to maintain euglycemia during exercise. Our results demonstrate that antecedent hypoglycemia, in type 1 diabetes, can produce acute counterregulatory failure during a subsequent episode of prolonged moderate-intensity exercise. The metabolic consequence of the blunted neuroendocrine and autonomic nervous system counterregulatory responses was an acute failure of endogenous glucose production to match the increased glucose requirements during exercise. These data indicate that counterregulatory failure may be a significant in vivo mechanism responsible for exercise-associated hypoglycemia in type 1 diabetes.

The aim of this study was to determine the effects of single and repeated episodes of clamped hypoglycemia on fibrinolytic balance, proinflammatory biomarkers, proatherothrombotic mechanisms, and endothelial function. Twenty healthy individuals (12 male and 8 female) were studied during separate 2-day randomized protocols. Day 1 consisted of either two 2-h hyperinsulinemic (812 ± 50 pmol/L)-euglycemic (5 ± 0.1 mmol/L) or hyperinsulinemic (812 ± 50 pmol/L)-hypoglycemic (2.9 ± 0.1 mmol/L) clamps. Day 2 consisted of a single 2-h hyperinsulinemic-hypoglycemic clamp. Two-dimensional Doppler ultrasound was used to determine brachial arterial endothelial function. Plasminogen activator inhibitor 1, vascular cell adhesion molecule-1, intracellular adhesion molecule-1, E-selectin, P-selectin, TAT (thrombin/antithrombin complex), tumor necrosis factor-α, and interleukin-6 responses were increased (P < 0.05) during single or repeated hypoglycemia compared with euglycemia. Endogenous and exogenous nitric oxide (NO)-mediated vasodilation were both impaired by repeated hypoglycemia. Neuroendocrine and autonomic nervous system (ANS) responses were also blunted by repeated hypoglycemia (P < 0.05). In summary, acute moderate hypoglycemia impairs fibrinolytic balance; increases proinflammatory responses, platelet activation, and coagulation biomarkers; and reduces NO-mediated endothelial function in healthy individuals. Repeated episodes of hypoglycemia further impair vascular function by additionally reducing exogenously NO-mediated endothelial function and increasing coagulation biomarkers. We conclude that despite reduced neuroendocrine and ANS responses, antecedent hypoglycemia results in greater endothelial dysfunction and an increased proatherothrombotic state compared with a single acute episode of hypoglycemia.

The aim of this study was to determine whether the duration of antecedent hypoglycemia regulates the magnitude of subsequent counterregulatory failure. A total of 31 lean healthy overnight-fasted individuals (16 men/15 women) were studied. There were 15 subjects (8 men/7 women) who underwent two separate 2-day randomized experiments separated by at least 2 months. On day 1, 2-h hyperinsulinemic (9 pmol · kg -1 · min -1 ) euglycemic (5.2 ± 0.1 mmol/l) or hypoglycemic (2.9 ± 0.1 mmol/l) glucose clamps (prolonged hypoglycemia) were carried out in the morning and afternoon. Of the other subjects, 16 participated in a 2-day study in which day 1 consisted of morning and afternoon short-duration hypoglycemia experiments (hypoglycemic nadir of 2.9 ± 0.1 mmol for 5 min), and 10 of these individuals underwent an additional 2-day study in which day 1 consisted of morning and afternoon intermediate-duration hypoglycemia (hypoglycemic nadir of 2.9 ± 0.1 mmol for 30 min). The next morning (day 2) all subjects underwent an additional 2-h hyperinsulinemic-hypoglycemic clamp (2.9 ± 0.1 mmol/l). The rate of fall of glucose (0.07 mmol/min) was carefully controlled during all hypoglycemic studies so that the glucose nadir was reached at 30 min. Despite equivalent day 2 plasma glucose and insulin levels, there were significant differences in counterregulatory physiological responses. Steady-state epinephrine, glucagon, growth hormone, cortisol, and pancreatic polypeptide levels were similarly significantly blunted (P < 0.01) by the differing duration day 1 hypoglycemia compared with day 1 euglycemia. Muscle sympathetic nerve activity and endogenous glucose production were also similarly blunted (P < 0.01) by day 1 hypoglycemia (relative to day 1 euglycemia). Day 2 hypoglycemic symptoms were significantly reduced (P < 0.01) after day 1 prolonged intermediate-but not short-duration hypoglycemia. In summary, two episodes of short-duration moderate hypoglycemia can produce significant blunting of key neuroendocrine and metabolic counterregulatory responses. Hypoglycemic symptom scores are reduced by prolonged but not short-duration prior hypoglycemia. We conclude that in healthy overnight fasted humans, 1) neuroendocrine, autonomic nervous system, and metabolic counterregulatory responses are sensitive to the blunting effects of even short-duration prior hypoglycemia, and 2) the duration of antecedent hypoglycemia results in a hierarchy of blunted physiological responses with hypoglycemic symptom awareness less vulnerable than neuroendocrine responses. Diabetes 49: [1897][1898][1899][1900][1901][1902][1903] 2000 N umerous studies have demonstrated that antecedent hypoglycemia can blunt subsequent counterregulatory responses to hypoglycemia (1-7). Recent work has focused on determining the in vivo factors and mechanisms responsible for this finding. Depth of antecedent hypoglycemia (8), number of prior episodes of hypoglycemia (2,4,8), and sex (9) can all independently regulate the magnitude of subsequent counterregulatory failure.To ...