Oral Glucose Load and Human Cutaneous Microcirculation: An Insight into Flowmotion Assessed by Wavelet Transform

Microcirculation in vivo has been assessed using non-invasive technologies such as laser Doppler flowmetry (LDF). In contrast to chronic hyperglycemia, known to induce microvascular dysfunction, the effects of short-term elevations in blood glucose on microcirculation are controversial. We aimed to assess the impact of an oral glucose load (OGL) on the cutaneous microcirculation of healthy subjects, quantified by LDF and coupled with wavelet transform (WT) as an interpretation tool. On two separate occasions, sixteen subjects drank either a glucose solution (75 g in 250 mL water) or water (equal volume). LDF signals were obtained in two anatomical sites (forearm and finger pulp) before and after each load (pre-load and post-load, respectively), in resting conditions and during post-occlusive reactive hyperemia (PORH). The WT allowed decomposition of the LDF signals into their spectral components (cardiac, respiratory, myogenic, sympathetic, endothelial NO-dependent). The OGL blunted the PORH response in the forearm, which was not observed with the water load. Significant differences were found for the cardiac and sympathetic components in the glucose and water groups between the pre-load and post-load periods. These results suggest that an OGL induces a short-term subtle microvascular impairment, probably involving a modulation of the sympathetic nervous system.

Characteristics and treatment responsiveness of patients with acromegaly and a paradoxical GH increase to oral glucose load

Objectives: We aimed to investigate the clinical, biochemical, histological and radiological characteristics as well as the response to somatostatin analogs (SSA) in a large cohort of acromegaly patients with a paradoxical GH response (PR) to oral glucose tolerance test (OGTT). Design: retrospective study. Methods: Of 110 patients with acromegaly included in our study, 30 (PR+; 27%) had a paradoxical GH increase of more than 25% relative to basal GH levels during OGTT. Results : At diagnosis, PR+ patients were older than PR- patients (52 ± 16 vs 44 ± 14 years, p<0.05) and had smaller pituitary tumours (40% microadenomas vs 19%, p<0.05), which were less often invasive (17 vs 35%, p<0.05), overall more secreting (IGF-1/tumoural surface: 2.35 ULN/cm² [0.28-9.06] vs 1.08 [0.17- 7.87], p=0.011), and more often hypointense on T2-weighted MRI (92 vs 48%, p=0.001). While the rate of remission after surgery was similar in the two groups (69%), a better response to SSA treatment was observed in PR+ patients, either before (IGF-1 reduction of > 50% after 3-6 months in 77 vs 49%, p=0.023) or after surgery (normalization of IGF-1 in 100 vs 44%, p=0.011). Conclusions: Our study demonstrates that in acromegaly, a paradoxical GH increase during OGTT is associated with particular features of somatotroph adenomas and with a better prognosis in terms of response to somatostatin analogs.

The effect of serum insulin on the blood pressure responses after oral glucose load in lean and centrally obese adult male subjects

Background: The vasodilator action of insulin might contribute to the reduction of blood pressure in the postprandial state and it remains to be clarified whether this action is impaired in the insulin- resistant obese state or not. Aims and Objective: The present study aimed to determine the blood pressure responses after an oral glucose load in lean and insulin resistant centrally obese adult male subjects. Materials and Methods: This study was carried out in eleven lean and eleven centrally obese adult male subjects. After a 75 g oral glucose load, blood pressures were measured at 15-minute intervals and the serum insulin level was determined at 30-minute intervals for two hours. Blood pressure was measured by indirect sphygmomanometry and serum insulin concentration was analyzed by ELISA method. Results: All centrally obese subjects were insulin resistant (HOMA-IR≥2.6). After oral glucose load, the per cent change in glucose-stimulated insulin responses at 30 minutes (626% vs 344%, p<0.05) and at 60 minutes (756% vs 417%, p<0.01) were significantly greater in the lean group than the centrally obese group. The fall in postprandial blood pressures started at 15 minutes and returned to baseline values at 120 minutes. The per cent change in SBP at 15 minutes (-2.2% vs -1.2%, p<0.05) and at 30 minutes (-3.2% vs -2.1%, p<0.05) were significantly greater in the lean group than the centrally obese group. Conclusion: The present findings suggest that attenuation in BP responses as well as a lesser change in glucose-stimulated insulin responses in the centrally obese subjects might be attributable to the presence of insulin resistance.

Sampling insulin in different tissue compartments using microdialysis: methodological aspects

Sampling the concentration of insulin in human skin using microdialysis is challenging because of low intracutaneous concentrations and low recovery, presumably due to adsorption of insulin to the microdialysis system. In this study, we aimed to (1) measure how the concentration of insulin varies in three different tissue compartments (intracutaneous, subcutaneous and intravenous) and (2) to study how much insulin is adsorbed to the microdialysis catheter membranes and tubing during a typical microdialysis experiment, both in vivo and in vitro. We hypothesized that (1) the concentration of insulin decreases from the intravenous compartment to the intracutaneous and subcutaneous tissue, and that (2) adsorption of insulin to the microdialysis membrane and tubing impairs the recovery of insulin from the tissue. In this experimental study, microdialysis catheters were inserted intracutaneously, subcutaneously and intravenously in 11 healthy subjects. Systemic endogenous hyperinsulinemia was induced by intake of an oral glucose load. Insulin concentration was measured in the dialysate and in the extracted samples from the catheter membrane and tubings. In vitro microdialysis was performed to investigate the temporal resolution of the adsorption. After an oral glucose load insulin concentration increased intravenously, but not in the intracutaneous or subcutaneous compartments, while glucose, lactate and pyruvate concentrations increased in all compartments. The adsorption of insulin to the microdialysis membrane in vivo was highest in the intravenous compartment (p = 0.01), compared to the intracutaneous and subcutaneous compartments. In vitro, the adsorption to the microdialysis membrane was highest one hour after sampling, then the concentration gradually decreased after three and five hours of sampling. The concentration of insulin in peripheral tissues is low, probably due to decreasing tissue vascularity. Adsorption of insulin to the microdialysis membrane is modest but time-dependent. This finding highlights the importance of a stabilization time for the microdialysis system before sampling tissue analytes.

Physical Exercise and Glucose Tolerance in Nigerian University Students

Background: Studying post-prandial fluctuations in blood glucose has high physiological and clinical relevance. Physical exercise is known to influence this fluctuation. Objectives: To determine the gender difference in glucose tolerance following physical exercise in a population of university students. Methods: A total of 146 students were randomly selected from the Olabisi Onabanjo University, Sagamu, Ogun State, southwest Nigeria. Following overnight fast, Oral Glucose Tolerance Test (OGTT) was carried out. Pre-exercise, fasting blood glucose (FBG) was measured at 0 mins, and after oral glucose load of 75 grams at 30 minutes intervals for 2 hours. The physical exercise involved cycling using a bicycle ergometer for an hour. Thereafter, OGTT was conducted again 1 hour post-exercise. Results: The ages of the subjects ranged from 20 years to 49 years. There were 73 (50.0%) females. The mean Body Mass Index (BMI) of 23.5±1.1 kg/m2 for females was comparable to 22.8±0.3 kg/m2 for the males (p = 0.571). Seven (9.6%) females were obese compared to 2 (2.7%) males. The mean post-prandial blood glucose increased from 71.6±1.6 mg/dl to 90.8±1.8 mg/dl after oral glucose load and thereafter to 88.0±4.2 mg/dl at 120 minutes among males. The post-exercise blood glucose patterns included a significant reduction in the mean FBS for males compared to females (64.5±1.9 mg/dl vs. 71.7±1.9 mg/dl; p = 0.001) Conclusions: Glucose tolerance with exercise is better in females than males. The clinical importance of physical exercise lies in its effect on glucose tolerance.

Relation of Diet-Induced Thermogenesis to Brown Adipose Tissue Activity in Healthy Men

Objective Human brown adipose tissue (BAT) is a thermogenic tissue activated by the sympathetic nervous system in response to cold. It contributes to energy expenditure (EE) and takes up glucose and lipids from the circulation. Studies in rodents suggest that BAT contributes to the transient rise in EE after food intake, so called diet-induced thermogenesis (DIT). We investigated the relationship between human BAT activity and DIT in response to glucose intake in 17 healthy volunteers. Methods We assessed DIT, cold induced thermogenesis (CIT) and maximum BAT activity at three separate study visits within two weeks. DIT was measured by indirect calorimetry during an oral glucose tolerance-test. CIT was assessed as the difference in EE after cold exposure of two hours duration as compared to warm conditions. Maximal activity of BAT was assessed by 18F-FDG-PET/MRI after cold exposure and concomitant pharmacological stimulation with Mirabegron. Results 17 healthy men (mean age 23.4 years, mean BMI 23.2 kg/m2) participated in the study. EE increased from 1908 (±181) kcal/24 hours to 2128 (±277) kcal/24 hours (p<0.0001, +11.5%) after mild cold exposure. An oral glucose load increased EE from 1911 (±165) kcal/24 hours to 2096 (±167) kcal/24 hours at 60 minutes (p<0.0001, +9.7%). The increase in EE in response to cold was significantly associated with BAT activity (R2=0.43, p=0.004). However, DIT was not associated with BAT activity (R2=0.015, p=0.64). Conclusion DIT after an oral glucose load was not associated with stimulated 18F-FDG uptake into BAT suggesting that DIT is independent from BAT activity in humans.

Acute Effect of Chili Consumption on Thermogenesis and Glycemic Response Following Oral Glucose Load in Men

Hypoglycemic and thermogenic effects are attributed to the capsaicinoid compounds (capsaicin). The aim of this study was to evaluate the acute effect of the consumption of 5g of chili pepper on thermogenesis and the glycemic response. In a pretest-post-test quasi-experimental study, the energy expenditure (EE) of 15 healthy men was evaluated by using indirect calorimetry at rest and with the consumption of 5g of Capsicum annum. In addition, the glycemic response after an oral glucose load was evaluated. After the consumption of C. annum, there was a significant increase in the EE of all the participants during the first few seconds postchili consumption. In sedentary participants, the consumption of chili pepper caused a significant decrease of blood glucose levels. The consumption of chili pepper has a potential immediate thermogenic effect during the first few seconds and, in sedentary people, it has a potential hypoglycemic effect.