Hypoglycemia In Healthy Men Research Articles

Lactate infusion increases brain energy content during euglycemia but not hypoglycemia in healthy men.

A special characteristic of the brain is the usage of lactate as alternative fuel instead of glucose to preserve its energy homeostasis. This physiological function is valid for sufficient cerebral glucose supply, as well as presumably during hypoglycemia, given that exogenous lactate infusion suppresses hormonal counterregulation. However, it is not yet clarified whether this effect is mediated by the use of lactate as an alternative cerebral energy substrate or any other mechanism. We hypothesized that under conditions of limited access to glucose (ie, during experimental hypoglycemia) lactate infusion would prevent hypoglycemia-induced neuroenergetic deficits in a neuroprotective way. In a randomized, double-blind, crossover study, lactate vs placebo infusion was compared during hyperinsulinemic-hypoglycemic clamps in 16 healthy young men. We measured the cerebral high-energy phosphate content-ie, adenosine triphosphate (ATP), phosphocreatine (PCr) and inorganic phosphate (Pi) levels-by 31 P-magnetic resonance spectroscopy as well as the neuroendocrine stress response. During euglycemia, lactate infusion increased ATP/Pi as well as PCr/Pi ratios compared with baseline values and placebo infusion. During hypoglycemia, there were no differences between the lactate and the placebo condition in both ratios. Hormonal counterregulation was significantly diminished upon lactate infusion. Our data demonstrate an elevated cerebral high-energy phosphate content upon lactate infusion during euglycemia, whereas there was no such effect during experimental hypoglycemia. Nevertheless, lactate infusion suppressed hypoglycemic hormonal counterregulation. Lactate thus adds to cerebral energy provision during euglycemia and may contribute to an increase in ATP reserves, which in turn protects the brain against neuroglucopenia under recurrent hypopglycemic conditions, eg, in diabetic patients.

Role of γ-aminobutyric acid signalling in the attenuation of counter-regulatory hormonal responses after antecedent hypoglycaemia in healthy men.

The attenuated counter-regulatory response to hypoglycaemia after antecedent hypoglycaemic episodes has been observed in animals to be associated with an increase in γ-aminobutyric acid (GABA) signalling. We therefore tested the hypothesis that the pharmacological suppression of GABAergic activity during a repeated hypoglycaemic episode enhances counter-regulatory responses. Fourteen healthy men participated in two experimental sessions each comprising three insulin-induced hypoglycaemic episodes. Before the third hypoglycaemic episode, participants received the GABA-antagonistic drug modafinil (200 mg orally) and placebo, respectively. In the placebo condition, the secretion of norepinephrine, adrenocorticotropic hormone, cortisol and growth hormone, and the perception of neuroglycopenic symptoms were attenuated during the third as compared with the first hypoglycaemic episode (each p < 0.05). Modafinil reversed this effect for the noradrenergic response (p < 0.05), while not significantly altering the attenuation of other hormonal responses and symptom perception (p > 0.3). Our findings indicate that increased GABAergic transmission could contribute to aspects of the attenuated counter-regulatory response after recurrent hypoglycaemia in humans.

NMDA receptor blockade by memantine does not prevent adaptation to recurrent hypoglycaemia in healthy men

Recurrent hypoglycaemia leads to an attenuation of hypoglycaemic symptoms and hormonal counterregulatory responses. This phenomenon poses a severe problem in the treatment of patients with diabetes mellitus, but the underlying neuroendocrine mechanisms are unclear. On the basis of animal experimental findings, we hypothesized that counterregulatory attenuation represents a basic adaptive learning process relying on synaptic long-term potentiation or depression. If so, attenuation should be prevented by blocking glutamatergic N-methyl-D-aspartate (NMDA) receptors. Sixteen healthy young men participated in two conditions, separated by 4 weeks. Participants received the NMDA antagonist memantine over 5 days (15 mg/day) in one condition and placebo in the other one. After 3 days of drug administration, participants underwent two hypoglycaemic clamps on day 4 and another one on day 5. We assessed blood concentrations of counterregulatory hormones (cortisol, ACTH, epinephrine, norepinephrine, growth hormone and glucagon) as well as subjective symptoms of hypoglycaemia and word-list recall as an indicator of short-term memory. Counterregulatory responses of all hormones as well as neuroglycopenic and autonomic symptom ratings showed robust attenuation following the third as compared to the first hypoglycaemia (p < 0.05). NMDA receptor antagonization by memantine impaired memory function but did not alter any neuroendocrine measure of counterregulatory attenuation (p > 0.17). Attenuation of the endocrine as well as symptomatic counterregulatory response to recurrent hypoglycaemia is not prevented by the NMDA receptor blocker memantine. Our results do not support the view that adaptation to repeated hypoglycaemia relies on NMDA receptor-mediated plastic processes involving long-term potentiation or depression.

Effects of Antecedent GABAA Activation With Alprazolam on Counterregulatory Responses to Hypoglycemia in Healthy Humans

OBJECTIVETo date, there are no data investigating the effects of GABAA activation on counterregulatory responses during repeated hypoglycemia in humans. The aim of this study was to determine the effects of prior GABAA activation using the benzodiazepine alprazolam on the neuroendocrine and autonomic nervous system (ANS) and metabolic counterregulatory responses during next-day hypoglycemia in healthy humans.RESEARCH DESIGN AND METHODSTwenty-eight healthy individuals (14 male and 14 female, age 27 ± 6 years, BMI 24 ± 3 kg/m2, and A1C 5.2 ± 0.1%) participated in four randomized, double-blind, 2-day studies. Day 1 consisted of either morning and afternoon 2-h hyperinsulinemic euglycemia or 2-h hyperinsulinemic hypoglycemia (2.9 mmol/l) with either 1 mg alprazolam or placebo administered 30 min before the start of each clamp. Day 2 consisted of a single-step hyperinsulinemic-hypoglycemic clamp of 2.9 mmol/l.RESULTSDespite similar hypoglycemia (2.9 ± 1 mmol/l) and insulinemia (672 ± 108 pmol/l) during day 2 studies, GABAA activation with alprazolam during day 1 euglycemia resulted in significant blunting (P < 0.05) of ANS (epinephrine, norepinephrine, muscle sympathetic nerve activity, and pancreatic polypeptide), neuroendocrine (glucagon and growth hormone), and metabolic (glucose kinetics, lipolysis, and glycogenolysis) counterregulatory responses. GABAA activation with alprazolam during prior hypoglycemia caused further significant (P < 0.05) decrements in subsequent glucagon, growth hormone, pancreatic polypeptide, and muscle sympathetic nerve activity counterregulatory responses.CONCLUSIONSAlprazolam activation of GABAA pathways during day 1 hypoglycemia can play an important role in regulating a spectrum of key physiologic responses during subsequent (day 2) hypoglycemia in healthy man.

Blocking AMPA receptor signalling by caroverine infusion does not affect counter-regulation of hypoglycaemia in healthy men

Glutamatergic pathways are assumed to play a critical role in the hormonal stress response to hypoglycaemia. In rats, glutamate signalling at the amino-3-hydroxy-5-methyl-4-isoxazol propionate (AMPA) receptor contributes to hormone release induced by behavioural stressors. We hypothesised that blocking the AMPA receptor by caroverine in healthy men would impair their perception of neuroglycopenia and thereby diminish hormonal counter-regulation as well as symptoms of hypoglycaemia, as a model of stress. In a balanced double-blind study, two hypoglycaemic clamp sessions (mean blood glucose 2.4 mmol/l for 50 min) were performed in ten healthy men during intravenous administration of 80 mg caroverine or placebo. We assessed concentrations of counter-regulatory hormones as well as subjective symptoms related to hypoglycaemia. AMPA receptor antagonisation by caroverine did not influence the perception of neuroglycopenic and autonomic hypoglycaemia-associated symptoms (p > 0.39 for all). Notwithstanding, caroverine did increase basal and counter-regulatory glucagon secretion (p < 0.002) and slightly enhanced counter-regulatory growth hormone concentrations (p = 0.07). Counter-regulatory release of ACTH, cortisol, adrenaline (epinephrine) and noradrenaline (norepinephrine) did not differ between conditions (p > 0.11 for all). Antagonising AMPA receptor signalling by caroverine infusion failed to diminish and even slightly amplified counter-regulatory hormone release during hypoglycaemia in healthy men. The discrepancy with previous findings in rats may be due to different dosages or administration routes and calls for further investigations on the role of AMPA receptor signalling in hypoglycaemia counter-regulation in humans.

Stimulation of both type I and type II corticosteroid receptors blunts counterregulatory responses to subsequent hypoglycemia in healthy man

Antecedent increases of corticosteroids can blunt counterregulatory responses to subsequent stress. Our aim was to determine whether prior activation of type I corticosteroid (mineralocorticoid) or type II corticosteroid (glucocorticoid) receptors blunts counterregulatory responses to subsequent hypoglycemia. Healthy volunteers participated in five randomized 2-day protocols. Day 1 involved morning and afternoon 2-h hyperinsulinemic (9 pmol.kg(-1).min(-1)) euglycemic clamps (PE; n = 14), hypoglycemic clamps (PH; n = 14), or euglycemic clamps with oral fludrocortisone (PE + F; type I agonist, 0.2 mg, n = 14), oral dexamethasone (PE + D; type II agonist, 0.75 mg, n = 13), or both (PE + F + D; n = 14). Day 2 was identical in all protocols and consisted of a 2-h hyperinsulinemic hypoglycemic clamp. Day 2 insulin (625 +/- 40 pmol/l) and glucose (2.9 +/- 0.1 mmol/l) levels were similar among groups. Levels of epinephrine, norepinephrine, glucagon, growth hormone, and MSNA were significantly blunted by prior activation of both type I and type II corticosteroid receptors to PE. Prior activation of both corticosteroid receptors also significantly blunted NEFA during subsequent hypoglycemia. Thus, levels of a wide spectrum of key counterregulatory mechanisms (neuroendocrine, ANS, and metabolic) were blunted by antecedent pharmacological stimulation of either type I or type II corticosteroid receptors in healthy man. These data suggest that activation of type I corticosteroid receptors in man can have acute and profound regulating effects on physiological stress in man. Both type I and type II corticosteroid receptors may be involved in the multiple mechanisms controlling counterregulatory responses to hypoglycemia in healthy man.

Antecedent hypoglycaemia attenuates vascular endothelial growth factor response to subsequent hypoglycaemia in healthy men

The plasma concentration of vascular endothelial growth factor (VEGF) has recently been shown to increase sharply in response to hypoglycaemia and, thus, has been proposed as having a role in hypoglycaemia counter-regulation. Many counter-regulatory hormones show a reduced response after antecedent hypoglycaemia. We therefore investigated whether this decrease in responsiveness with repetitive hypoglycaemia also pertains to VEGF. Three hypoglycaemic clamp experiments were performed on two consecutive days in 15 healthy men. VEGF response was assessed during the first and last hypoglycaemic period. As expected, plasma VEGF concentrations rose markedly during the clamps (P < 0.001). The increase was distinctly blunted during the third (+13 +/- 8 pg/ml) as compared with the first (+54 +/- 18 pg/ml) hypoglycaemic clamp (P = 0.046). This data confirms that circulating VEGF concentrations increase acutely during hypoglycaemia. Like the counter-regulatory hormones, the hypoglycaemia-induced rise in VEGF is attenuated after antecedent hypoglycaemia. The origin of increased systemic VEGF concentration during hypoglycaemia and its physiological role remains to be defined.

Processing of food stimuli is selectively enhanced during insulin-induced hypoglycemia in healthy men

Recently it has been reported that during insulin-induced hypoglycemia selective attention is directed to food stimuli suggesting an adaptive cognitive strategy to escape from this potentially dangerous metabolic state. Here, we tested this hypothesis using a short-term memory task. We also aimed to define a hypoglycemic threshold level at which such an adaptive cognitive strategy first occurs. Fifteen healthy men underwent stepwise hypoglycemic (plasma glucose: 4.1-3.6-3.1-2.6 mmol/l) and euglycemic clamp experiments. Clamps were performed in a single blind fashion within a cross-over design with the order balanced across subjects. During the clamps cognitive function tests (short-term recall of food-related and non-food-related words; Stroop task) were applied at baseline and each hypoglycemic plateau, and at the corresponding time intervals of the euglycemic clamp. Performance on all cognitive function tests applied deteriorated during the hypoglycemic as compared to the euglcemic clamp (all P<0.02). Separate analyses at each hypoglycemic plateau revealed that food and non-food related short-term memory was similar during baseline and mild hypoglycemia. However, at the hypoglycemic target level of 2.6 mmol/l recall of food related words was higher than non-food related words when compared to the euglycemic control clamp condition (p=0.024). Performance on the word-color conflict Stroop task became significantly impaired first at the lowest hypoglycemic plateau (2.6 mmol/l), while performance on the Stroop subtests 'color naming' and 'word reading' were already impaired at higher plasma glucose levels (3.6 and 3.1 mmol/l; respectively). Collectively, data of the Stroop task indicate that the control of attention via executive mechanisms is less sensitive to insulin-induced hypoglycemia than pre-attentive automated stimulus processing (reading, naming). If executive control of attention becomes affected by hypoglycemia, cognitive resources appear to be preferentially allocated to the processing of food stimuli.

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.

The effects of KATP channel modulators on counterregulatory responses and cognitive function during acute controlled hypoglycaemia in healthy men: a pilot study.

To examine the effects of agents that alter potassium adenosine triphosphate (KATP) channel activity in beta-cells on cognitive function and counterregulatory hormone responses during acute hypoglycaemia, given the physiological similarities between the pancreatic beta-cell and the hypothalamic glucose-sensitive neurones (GSN) and the widespread distribution of sulphonylurea receptors in neuronal cells throughout the brain. Ten healthy males were studied on four occasions and in random order underwent three stepped hypoglycaemic (plasma glucose aims: 3.4, 2.8, 2.4 mmol/l) and one euglycaemic (plasma glucose aim: 5 mmol/l) insulin clamps. Prior to each hypoglycaemic study, volunteers received either 10 mg glibenclamide, or 5 mg/kg diazoxide or placebo orally. Cognitive function, symptom scores and counterregulatory hormone responses were measured at each glycaemic level. There was no statistically significant effect of either drug on the symptoms generated or the counterregulatory hormonal response during hypoglycaemia. However, cognitive function was better preserved during hypoglycaemia in the glibenclamide-treated arm, particularly four-choice reaction time which deteriorated at a plasma glucose 2.5 mmol/l compared with 3.0 mmol/l with diazoxide (P = 0.015) and 2.9 mmol/l with placebo (P = 0.114). Single doses of pharmacological agents which alter membrane KATP channel activity do not affect the counterregulatory response to hypoglycaemia but may modify cognitive function during cerebral glucopenia. The unexpected effects of glibenclamide on cortical function suggest a novel action of sulphonylureas that warrants further investigation.

Adaptation of cognitive function to hypoglycemia in healthy men.

Antecedent hypoglycemia reduces hypoglycemic counterregulation and symptoms, thereby provoking the hypoglycemia unawareness syndrome. The effects of antecedent hypoglycemia on hypoglycemia-induced cognitive dysfunction are less well established. To determine whether antecedent hypoglycemia also reduces hypoglycemic cognitive dysfunction, we performed stepwise hypoglycemic clamp experiments (4.1, 3.6, 3.1, and 2.6 mmol/l) during a 6-h period in 30 young healthy men. A total of 15 subjects additionally received a 2.5-h antecedent hypoglycemic clamp (3.1 mmol/l) on the preceding day (prior-hypo group), whereas the other 15 subjects did not (control group). Cognitive function was assessed by auditory-evoked brain potentials (AEBPs) and reaction time during a vigilance task and short-term memory recall. Tests were performed during the stepwise hypoglycemic clamp at baseline and at each hypoglycemic plateau. In both groups, performance on all measures of cognitive function deteriorated during stepwise hypoglycemia (all P < 0.01). However, after antecedent hypoglycemia, the hypoglycemia-induced decrease in the amplitude of the P3 of the AEBP was distinctly reduced compared with the control condition (P < 0.05). Also, short-term memory performance was less impaired in the prior-hypo group than in the control group (P < 0.005), and a minor hypoglycemic impairment of reaction time (P < 0.05) was evident in the prior-hypo group. Data provide evidence that a single episode of mild antecedent hypoglycemia (3.1 mmol/l) attenuates several aspects of cognitive dysfunction during subsequent hypoglycemia 18-24 h later.

Hypoglycaemia leads to an increased QT interval in normal men.

Hypoglycaemia is presumed to be the cause of death in about 3% of insulin-treated diabetic patients. Some of these patients suffer from hypoglycaemic brain damage, but the majority have no evident brain damage and are supposed to have died from other causes such as a cardiac arrhythmia. The putative mechanism is a hypoglycaemia-induced prolongation of the QT interval which increases the risk of malignant ventricular tachycardia. The aim of the present study was to examine the electrocardiogram during and after hypoglycaemia in healthy men. To that end, hypoglycaemia was induced by an intravenous infusion of insulin (2.5 mU kg-1 min-1) in 10 healthy men to reach a venous blood glucose level of 2.1 +/- 0.3 mmol l-1 for 65 +/- 9 min. Before hypoglycaemia, after 20 and 50 min of hypoglycaemia and 20 and 45 min after normalization of the blood glucose, the QT interval was measured by a ruler and corrected for the heart rate. Results are given as mean +/- SD and comparisons were made with an ANOVA, except for symptom scores and plasma adrenaline where non-parametric tests were used. When this indicated significance, further analysis was performed with a two-tailed t-test. During hypoglycaemia the corrected QT interval increased from 380 +/- 20 ms1/2 to 440 +/- 30 ms1/2 (P < 0.001), and the amplitude of the T wave decreased (P = 0.002). The serum potassium level decreased from 4.3 +/- 0.3 mmol l-1 to 3.5 +/- 0.2 mmol l-1 (P < 0.001) and the plasma adrenaline concentration increased from 0.20 +/- 0.04 nmol l-1 to 2.46 +/- 2.58 nmol l-1 (P < 0.01). The results of this study confirm that a prolongation of the QT interval occurs during hypoglycaemia, but the significance of this finding still has to be proven.

Theophylline enhances glucose recovery after hypoglycemia in healthy man and in type I diabetic patients

The principal mediators of glucose counterregulation (glucagon and epinephrine) use intracellular cyclic adenosine monophosphate (cAMP) to mediate glucose release. Since theophylline increases cAMP (by inhibiting its decomposition), we investigated the effect of theophylline on glucose recovery after insulin-induced hypoglycemia. Eleven healthy subjects and nine type I (insulin-dependent) diabetic patients each participated in two experiments in randomized order, receiving on both days an insulin bolus of 0.15 IU/kg soluble insulin. On one day, theophylline (intravenous [IV] bolus of 220 mg followed by IV infusion of 1 mg/kg/h) was administered from 1 hour before induction of hypoglycemia until the end of the study period. On the other day, NaCl was administered. Plasma glucose before induction of hypoglycemia was equal on the 2 study days. The plasma glucose area under the curve (AUC) was larger with theophylline than with NaCl ( P = .04 for diabetic patients and P = .003 for healthy subjects). During the most active phase of glucose counterregulation, the rate of increase of plasma glucose was larger with theophylline ( P = .003 for diabetic patients and P = .03 for healthy subjects). The incremental AUC for cAMP was larger with theophylline for diabetic patients ( P = .01). For healthy subjects, cAMP was greater with theophylline 30 minutes after insulin ( P = .03). In conclusion, glucose recovery after hypoglycemia is significantly increased when theophylline is administered in an asthma dosage before hypoglycemia is indeced. This may be due to a significant enhancement of the cAMP response.

Plasma glucagon and glucose recovery after hypoglycemia: the effect of total autonomic blockade.

The role of the autonomic nervous system in the glucagon response to hypoglycemia has not been fully clarified. We have studied the effect of total pharmacological blockade of the autonomic nervous system (concomitant alpha- and beta-adrenergic blockade with simultaneous atropine injection) and of isolated alpha-adrenergic blockade on hormonal responses to hypoglycemia and on blood glucose recovery after hypoglycemia in healthy subjects. Neither of the pharmacological blockades had any significant effects on plasma glucagon responses to hypoglycemia nor had they any effect on the rate of blood glucose recovery after hypoglycemia. We conclude that the autonomic nervous system has no major influence on the glucagon response to hypoglycemia in healthy man. Changes in autonomic nervous activity are not essential for blood glucose recovery after hypoglycemia in healthy man.