Epinephrine effects on insulin-glucose dynamics: the labeled IVGTT two-compartment minimal model approach

Hypothalamus-sympathetic-liver axis mediates the early phase of stress-induced hyperglycemia in the male mice

Rapid glucose supply is crucial for animal survival during stress response. How the timescale of stress-induced glucose release precisely controlled by hypothalamic corticotropin-releasing hormone (CRH) neurons remains unclear. Here, we show that stress-induced hyperglycemia can be divided into at least two stages in male mice: the first fast stage is mediated by hypothalamus (paraventricular to ventromedial hypothalamus)-sympathetic (raphe pallidus nucleus to intermediolateral nucleus)-liver (HSL) axis activity; the second delayed stage is mediated by adrenal activity. Blocking the activity of HSL axis impairs predatory evoked flight responses, indicating that the HSL pathway activity is necessary for stress coping. We further reveal the intracellular signal cascade for CRH signal in the hypothalamus, which is mediated by GABAA receptor β3 subunit phosphorylation at S408/409, results in prevention of GABAA receptor membrane recruitment. Thus, we uncovered the precise timescale of glucose supply during stress which is mediated by adrenal independent HSL and adrenal dependent pathway respectively.

Variability in Estimated Modelled Insulin Secretion

BACKGROUND

The ability to measure insulin secretion from pancreatic beta cells and monitor glucose-insulin physiology is vital to current health needs. C-peptide has been used successfully as a surrogate for plasma insulin concentration. Quantifying the expected variability of modelled insulin secretion will improve confidence in model estimates.

METHODS

Forty-three healthy adult males of Māori or Pacific peoples ancestry living in New Zealand participated in an frequently sampled, intravenous glucose tolerance test (FS-IVGTT) with an average age of 29 years and a BMI of 33 kg/m². A 2-compartment model framework and standardized kinetic parameters were used to estimate endogenous pancreatic insulin secretion from plasma C-peptide measurements. Monte Carlo analysis (N = 10 000) was then used to independently vary parameters within ±2 standard deviations of the mean of each variable and the 5th and 95th percentiles determined the bounds of the expected range of insulin secretion. Cumulative distribution functions (CDFs) were calculated for each subject for area under the curve (AUC) total, AUC Phase 1, and AUC Phase 2. Normalizing each AUC by the participant's median value over all N = 10 000 iterations quantifies the expected model-based variability in AUC.

RESULTS

Larger variation is found in subjects with a BMI > 30 kg/m², where the interquartile range is 34.3% compared to subjects with a BMI ≤ 30 kg/m² where the interquartile range is 24.7%.

CONCLUSIONS

Use of C-peptide measurements using a 2-compartment model and standardized kinetic parameters, one can expect ~±15% variation in modelled insulin secretion estimates. The variation should be considered when applying this insulin secretion estimation method to clinical diagnostic thresholds and interpretation of model-based analyses such as insulin sensitivity.

Associations between central nervous system serotonin, fasting glucose, and hostility in African American females

BACKGROUND

Previous research has shown an association between hostility and fasting glucose in African American women. Central nervous system serotonin activity is implicated both in metabolic processes and in hostility related traits.

PURPOSE

The purpose of this study is to determine whether central nervous system serotonin influences the association between hostility and fasting glucose in African American women.

METHODS

The study consisted of 119 healthy volunteers (36 African American women, 27 White women, 21 White males, and 35 African American males, mean age 34 ± 8.5 years). Serotonin related compounds were measured in cerebrospinal fluid. Hostility was measured by the Cook-Medley Hostility Scale.

RESULTS

Hostility was associated with fasting glucose and central nervous system serotonin related compounds in African American women only. Controlling for the serotonin related compounds significantly reduced the association of hostility to glucose.

CONCLUSIONS

The positive correlation between hostility and fasting glucose in African American women can partly be explained by central nervous system serotonin function.

Type 2 diabetes mellitus: a disease of the governance of the glucose-insulin system: an experimental metabolic control analysis study

BACKGROUND AND AIMS

The relatives role of each component of the glucose-insulin system in determining hyperglycemia in type 2 diabetes is still under debate. Metabolic Control Analysis (MCA) quantifies the control exerted by each component of a system on a variable of interest, by computing the relevant coefficients of control (CCs), which are systemic properties. We applied MCA to the intravenous glucose tolerance test (IVGTT) to quantify the CCs of the main components of the glucose-insulin system on intravenous glucose tolerance.

METHODS AND RESULTS

We combined in vivo phenotyping (IVGTT/euglycaemic insulin clamp) and in silico modeling (GLUKINSLOOP.1) to compute the CCs of intravenous glucose tolerance in healthy insulin-sensitive (n = 9, NGR-IS), healthy insulin-resistant (n = 7, NGR-IR) and subdiabetic hyperglycemic (n = 8, PreT2DM) individuals and in patients with newly diagnosed type 2 diabetes (n = 7, T2DM). Altered insulin secretion and action were documented in NGR-IR and PreT2DM groups, but only 1st phase insulin secretion was significantly lower in T2DM than in PreT2DM (p < 0.05). The CCs changed little in the nondiabetic groups. However, several CCs were significantly altered in the patients (e.g. CCs of beta cell: -0.75 ± 0.10, -0.64 ± 0.15, -0.56 ± 0.09 and -0.19 ± 0.04 in NGR-IS, NGR-IR, PreT2DM and T2DM, respectively; p < 0.01 by MANOVA), and they could not be corrected by matching in silico nondiabetic and T2DM groups for 1st phase secretion.

CONCLUSIONS

Type 2 diabetes is characterized not only by loss of function of the elements of the glucose-insulin system, but also by changes in systemic properties (CCs). As such, it could be considered a disease of the governance of the glucose-insulin system.

Sympathetic inhibition attenuates hypoxia induced insulin resistance in healthy adult humans

Acute exposure to hypoxia decreases insulin sensitivity in healthy adult humans; the mechanism is unclear, but increased activation of the sympathetic nervous system may be involved. We have investigated the hypothesis that short-term sympathetic inhibition attenuates hypoxia induced insulin resistance. Insulin sensitivity (via the hyperinsulinaemic euglycaemic clamp) was determined in 10 healthy men (age 23 ± 1 years, body mass index 24.2 ± 0.8 kg m⁻² (means ± SEM)), in a random order, during normoxia (FIO₂ =0.21), hypoxia (FIO₂ =0.11), normoxia and sympathetic inhibition (via 48 h transdermal administration of the centrally acting α2-adrenergic receptor agonist, clonidine), and hypoxia and sympathetic inhibition.Oxyhaemoglobin saturation (pulse oximetry) was decreased (P<0.001) with hypoxia (63 ± 2%) compared with normoxia (96 ± 0%), and was unaffected by sympathetic inhibition (P>0.25). The area under the noradrenaline curve (relative to the normoxia response) was increased with hypoxia (137 ± 13%; P =0.02); clonidine prevented the hypoxia induced increase (94 ± 14%; P =0.43). The glucose infusion rate (adjusted for fat free mass and circulating insulin concentration) required to maintain blood glucose concentration at 5 mmol l⁻¹ during administration of insulin was decreased in hypoxia compared with normoxia (225 ± 23 vs. 128 ± 30 nmol (kg fat free mass)⁻¹ pmol l⁻¹ min⁻¹; P =0.03), and unchanged during normoxia and sympathetic inhibition (219 ± 19; P =0.86) and hypoxia and sympathetic inhibition (169 ± 23; P =0.23). We conclude that short-term sympathetic inhibition attenuates hypoxia induced insulin resistance.

Glucoregulatory consequences and cardiorespiratory parameters in rats exposed to chronic-intermittent hypoxia: effects of the duration of exposure and losartan

BACKGROUND

Obstructive sleep apnea (OSA) is associated with glucose intolerance. Both chronic sleep disruption and recurrent blood oxygen desaturations (chronic-intermittent hypoxia, CIH) may cause, or exacerbate, metabolic derangements.

METHODS

To assess the impact of CIH alone, without accompanying upper airway obstructions, on the counter-regulatory response to glucose load and cardiorespiratory parameters, we exposed adult male Sprague-Dawley rats to CIH or sham room air exchanges for 10 h/day for 7, 21, or 35 days and then, 1 day after conclusion of CIH exposure, conducted intravenous glucose-tolerance tests (ivgtt) under urethane anesthesia. Additional rats underwent 35 days of CIH followed by 35 days of regular housing, or had 35 day-long CIH exposure combined with daily administration of the type 1 angiotensin II receptor antagonist, losartan (15 mg/kg, p.o.), and then were also subjected to ivgtt.

RESULTS

Compared with the corresponding control groups, CIH rats had progressively reduced glucose-stimulated insulin release and impaired glucose clearance, only mildly elevated heart rate and/or arterial blood pressure and slightly reduced respiratory rate. The differences in insulin release between the CIH and sham-treated rats disappeared in the rats normally housed for 35 days after 35 days of CIH/sham exposure. The losartan-treated rats had improved insulin sensitivity, with no evidence of suppressed insulin release in the CIH group.

CONCLUSION

In adult rats, the glucose-stimulated insulin release is gradually suppressed with the duration of exposure to CIH, but the effect is reversible. Elimination of the detrimental effect of CIH on insulin release by losartan suggests that CIH disrupts glucoregulation through angiotensin/catecholaminergic pathways. Accordingly, treatment with continuous positive airway pressure may ameliorate pre-diabetic conditions in OSA patients, in part, by reducing sympathoexcitatory effects of recurrent nocturnal hypoxia.

Citalopram improves metabolic risk factors among high hostile adults: results of a placebo-controlled intervention

Hostility is associated with a number of metabolic risk factors for cardiovascular disease, including waist-hip ratio, glucose, and triglycerides. Along with hostility, many of these measures have also been shown to be associated with reduced central serotonergic function. We have previously reported that a citalopram intervention was successful in reducing hostility by self-report assessment (Kamarck et al., 2009). Here we examine the effects of this serotonergic intervention on metabolic risk factors in the same sample. 159 healthy adults with elevated hostility scores were randomized to citalopram or placebo for a 2-month period. Citalopram favorably changed metabolic risk factors, including waist circumference (p=.003), glucose (p=.02), HDL cholesterol (p=.04), triglycerides (p=.03), insulin sensitivity (p=.045) and diastolic blood pressure by automated assessment (p=.0021). All of these metabolic changes were significantly mediated by treatment-related changes in body mass index (in most cases, p<.01). In addition, the changes in blood glucose were significantly mediated by treatment-related changes in hostility (p<.05). Mechanisms accounting for these associations remain to be explored.

Plasma epinephrine predicts fasting glucose in centrally obese African-American women

The high prevalence of diabetes in African-American (AA) women has been widely assumed to be related to the greater prevalence of obesity in this group. Catecholamine release acting on central adipose tissue has been proposed to be a contributing factor. The aim of this article was to examine the interaction of plasma catecholamines and central adiposity on fasting and nonfasting glucose levels in two separate samples. In both studies, the women were healthy, nondiabetic of similar age. In addition, both studies assessed plasma epinephrine (EPI) and norepinephrine (NOREPI) levels collected at three time points. In study 1, catecholamines were measured during a standardized laboratory mental stress task and in study 2, they were measured during the initial phase (10 min) of an intravenous glucose tolerance test (IVGTT). Results from both studies revealed significant effects of EPI on fasting glucose in the obese women. In study 1, mean EPI levels were significantly related to fasting glucose in AA women with high trunk fat (beta = 0.60, P < 0.001). Because high BMI was associated with high trunk fat in women, we used BMI >30 as a proxy for high trunk fat (>32%) in study 2. In study 2, EPI response to the glucose bolus was a strong predictor of fasting glucose in AA women with BMI >30 (beta = 0.75, P < 0.003). We conclude that the effect of central adiposity on fasting glucose may be moderated by plasma EPI. This suggests that adrenal medullary activity could play a role in the pathophysiology of type 2 diabetes.

Hostility and fasting glucose in African American women

OBJECTIVE

To examine whether the relationship of hostility (HOST) to fasting glucose indices is moderated by sex and race. HOST has been associated with abnormalities in glucose metabolism. Prior studies suggested that this association may be more prevalent in women and in African American (AA) individuals.

METHODS

A total of 565 healthy AA and white (W) men and women (mean age = 33 +/- 6 years) were assessed. HOST was measured by the 27-item version of the Cook Medley HOST Scale. The moderating effects of sex and race were evaluated for the associations of HOST to fasting glucose, insulin, and insulin sensitivity (HOMA-IR).

RESULTS

Analysis showed a moderating effect of sex and race on the association of HOST to fasting glucose (p = .03), but not for insulin (p = .12). Analysis of HOMA-IR revealed a trend (p = .06) for the interaction. Stratified analyses by race and sex revealed a positive association between HOST and fasting glucose only in AA women, which remained significant after controlling for age and body mass index.

CONCLUSION

A relationship between HOST and fasting glucose was evident in AA women only, a group that has twice the risk of developing Type 2 diabetes compared with W women. Further studies are needed to elucidate the mechanisms by which HOST may affect glucose metabolism in AA women.

Effects of an intravenous endotoxin challenge on glucose and insulin dynamics in horses

OBJECTIVE

To evaluate the effects of endotoxin administered IV on glucose and insulin dynamics in horses.

ANIMALS

16 healthy adult mares.

PROCEDURES

Each week of a 2-week randomized crossover study, each horse received an IV injection (duration, 30 minutes) of Escherichia coli O55:B5 lipopolysaccharide (LPS) in 60 mL of sterile saline (0.9% NaCl) solution (20 ng/kg) or sterile saline solution alone (control treatment). Frequently sampled IV glucose tolerance test procedures were performed at 24 hours before (baseline) and 24 and 48 hours after injection; glucose and insulin dynamics were assessed via minimal model analysis.

RESULTS

13 of 16 horses had a clinical response to LPS, which was characterized by mild colic and leukopenia. Before treatment, mean +/- SD insulin sensitivity was 2.9 +/- 1.9 x 10(4) L x min(1) x mU(1); this significantly decreased to 0.9 +/- 0.9 x 10(4) L x min(1) x mU(1) 24 hours after treatment (69% reduction) and was 1.5 +/- 0.9 x 10(4) L x min(1) x mU(1) 48 hours after treatment. At baseline, mean +/- SD acute insulin response to glucose was 520 +/- 196 mU x min x L(1); this significantly increased to 938 +/- 620 mU x min x L(1) (80% increase) and 755 +/- 400 mU x min x L(1) (45% increase) at 24 and 48 hours after LPS treatment, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Compared with baseline values, insulin sensitivity was decreased for 24 hours after IV injection of LPS, and affected horses had a compensatory pancreatic response. These disturbances in glucose and insulin dynamics may contribute to development of laminitis in horses.

Effects of glucose on responsiveness to change in young adult and middle-aged rats

After a 0.5-, 15-, or 30-min intertrial interval, first entries of a novel Y-maze arm that had changed in brightness, percent entries of the arm, and percent time spent in this arm during a 1-min period were recorded in 4-month-old hooded rats following 6 or 30 min of free exploration of both arms. From the results, it was concluded that maximal responsiveness to the changed (or novel) arm occurred after 6 min of exploration and a 30-min intertrial interval. In a second experiment, responsiveness to change was assessed in young adult (4 months) and middle-aged (18 months) rats after 6 min of free exploration followed by an intraperitoneal injection of distilled water, or 50 or 100 mg/kg d-glucose before testing 20 min later. While glucose increased first entries of the changed arm in all rats, longer-term responsiveness in the form of percent entries of the novel arm and time spent in the novel arm was increased only for young adults. Although the results suggested age-specific glucose-enhanced consolidation or retrieval of change-related information, it was also possible that the treatment had differentially increased preferences for novelty in the two age groups. This possibility should be addressed in future research.