Influence of physical inactivity on arterial compliance during a glucose challenge

The impact of preconditioning exercise on the vascular response to an oral glucose challenge

Exercise elicits direct benefits to insulin sensitivity but may also indirectly improve glucose uptake by hemodynamic conditioning of the vasculature. The purpose of this study was to examine the modifying effect of 3 different types of exercise on the vascular response to an oral glucose challenge. Twenty healthy adults (9 women, 11 men; aged 23 ± 3 years) completed a standard oral glucose tolerance test (OGTT) at rest, as well as 1.5 hours after moderate continuous cycling exercise (30 min; 65% peak oxygen consumption), high-intensity interval cycling exercise (10 × 1 min at 90% peak heart rate), and lower-load higher-repetition resistance exercise (25-35 repetitions/set, 3 sets). Brachial and superficial femoral artery blood flow, conductance, and oscillatory shear index were measured throughout the OGTT. Regardless of rested state or exercise preconditioning, the OGTT induced reductions in brachial artery blood flow and conductance (p < 0.001), and transient increases in brachial and superficial femoral artery oscillatory shear index and retrograde blood flow (p < 0.01). Continuous cycling and resistance exercise were followed with a small degree of protection against prolonged periods of oscillatory flow. Our findings imply transient peripheral vasoconstriction and decreased limb blood flow during a standard OGTT, for which prior exercise was unable to prevent in healthy adults. Novelty: We investigated the impact of continuous, interval, and resistance exercise on the hemodynamic response to an OGTT. Our findings suggest decreased upper-limb blood flow during an OGTT is not prevented by prior exercise in healthy adults.

Quantification of Mitochondrial Oxidative Phosphorylation in Metabolic Disease: Application to Type 2 Diabetes

Type 2 diabetes (T2D) is a growing health concern with nearly 400 million affected worldwide as of 2014. T2D presents with hyperglycemia and insulin resistance resulting in increased risk for blindness, renal failure, nerve damage, and premature death. Skeletal muscle is a major site for insulin resistance and is responsible for up to 80% of glucose uptake during euglycemic hyperglycemic clamps. Glucose uptake in skeletal muscle is driven by mitochondrial oxidative phosphorylation and for this reason mitochondrial dysfunction has been implicated in T2D. In this review we integrate mitochondrial function with physiologic function to present a broader understanding of mitochondrial functional status in T2D utilizing studies from both human and rodent models. Quantification of mitochondrial function is explained both in vitro and in vivo highlighting the use of proper controls and the complications imposed by obesity and sedentary lifestyle. This review suggests that skeletal muscle mitochondria are not necessarily dysfunctional but limited oxygen supply to working muscle creates this misperception. Finally, we propose changes in experimental design to address this question unequivocally. If mitochondrial function is not impaired it suggests that therapeutic interventions and drug development must move away from the organelle and toward the cardiovascular system.

An accumulation of muscle macrophages is accompanied by altered insulin sensitivity after reduced activity and recovery

BACKGROUND

Mechanisms underlying physical inactivity-induced insulin resistance are not well understood. In addition to a role in muscle repair, immune cell populations such as macrophages may regulate insulin sensitivity.

AIM

The aim of this study was to examine if the dynamic changes in insulin sensitivity during and after recovery from reduced physical activity corresponded to changes in skeletal muscle macrophages.

METHODS

In this prospective clinical study, we collected muscle biopsies from healthy older adults (70 ± 2 years, n = 12) before and during a hyperinsulinaemic-euglycaemic clamp and this occurred before (PRE) and after 2-week reduced physical activity (RA), and following 2-week of recovery (REC). Insulin sensitivity (hyperinsulinaemic-euglycaemic clamp), skeletal muscle mRNA expression of inflammatory markers, and immunofluorescent quantification of skeletal muscle macrophages, myofibre-specific satellite cell and capillary content were assessed.

RESULTS

Insulin sensitivity was decreased following reduced activity and rebounded following recovery above PRE levels. We observed an increase (P < 0.01) in muscle macrophages (CD68⁺ CD206⁺ : 190 [55, 324]; CD11b⁺ CD206⁺ : 117 [28, 205]% change from PRE) and CD68 (2.4 [1.4, 3.4]-fold) and CCL2 (1.9 [1.3, 2.5]-fold) mRNA following RA concurrent with increased (P < 0.03) satellite cells (55 [6, 104]%) in slow-twitch myofibres. Moreover, the distance of satellite cells to the nearest capillary was increased 7.7 (1.7, 13.7) µm in fast-twitch myofibres at RA (P = 0.007). Changes in macrophages were positively associated with increased insulin sensitivity following RA (R > 0.57, P < 0.05).

CONCLUSION

These findings suggested that a dynamic response of skeletal muscle macrophages following acute changes in physical activity in healthy older adults is related to insulin sensitivity.

Effects of exercise intensity on vascular and autonomic components of the baroreflex following glucose ingestion in adolescents

Purpose

To investigate the effects of an oral glucose tolerance test (OGTT) on baroreflex sensitivity (BRS) in a sample of healthy adolescents, and how acute exercise bouts of different intensities alter the effects of the OGTT on BRS.

Methods

Thirteen male adolescents (14.0 ± 0.5 years) completed three conditions on separate days in a counterbalanced order: (1) high-intensity interval exercise (HIIE); (2) moderate-intensity interval exercise (MIIE); and (3) resting control (CON). At ~ 90 min following the conditions, participants performed an OGTT. Supine heart rate and blood pressure were monitored continuously at baseline, 60 min following the conditions, and 60 min following the OGTT. A cross-spectral method (LFgain) was used to determine BRS gain. Arterial compliance (AC) was assessed as the BRS vascular component. LFgain divided by AC (LFgain/AC) was used as the autonomic component.

Results

Although non-significant, LFgain moderately decreased post-OGTT when no exercise was performed (pre-OGTT = 24.4 ± 8.2 ms mmHg^− 1; post-OGTT = 19.9 ± 5.6 ms mmHg^− 1; ES = 0.64, P > 0.05). This was attributed to the decrease in LFgain/AC (pre-OGTT = 1.19 ± 0.5 ms µm^− 1; post-OGTT = 0.92 ± 0.24 ms µm^− 1; ES = 0.69, P > 0.05). Compared to CON (Δ = − 4.4 ± 8.7 ms mmHg^− 1), there were no differences for the pre–post-OGTT delta changes in LF/gain for HIIE (Δ = − 3.5 ± 8.2 ms mmHg^− 1) and MIIE (Δ = 1.3 ± 9.9 ms mmHg^− 1) had no effects on BRS following the OGTT (all ES < 0.5). Similarly, compared to CON (Δ = − 0.23 ± 0.40 ms µm^− 1) there were no differences for the pre–post-OGTT delta changes in LF/gain for HIIE (Δ = − 0.22 ± 0.49 ms µm^− 1) and MIIE (Δ = 0.13 ± 0.36 ms µm^− 1).

Conclusion

A moderate non-significant decrease in BRS was observed in adolescents following a glucose challenge with no apparent effects of exercise.

Postprandial augmentation index is reduced in adults with prediabetes following continuous and interval exercise training

NEW FINDINGS

What is the central question of this study? We compared high-intensity interval versus continuous training on fasting and postprandial arterial stiffness in people with prediabetes. What is the main finding and its importance? We show, for the first time, that exercise improves the augmentation index during the postprandial state, but not the fasted state, in adults with prediabetes. However, the fasted augmentation index improved in relationship to exercise dose, as assessed by kilocalories per session. Collectively, these findings suggest that short-term exercise can improve arterial compliance in adults with prediabetes. Therefore, lifestyle interventions designed to reduce arterial stiffness could have considerable clinical impact.

ABSTRACT

People with prediabetes have elevated risk for cardiovascular disease, in part, owing to arterial stiffness mediated by low insulin sensitivity. However, the effect the intensity and/or amount (i.e. kilocalories per session) of short-term exercise training on fasting and postprandial arterial stiffness is unknown. We tested the hypothesis that increased intensity and dose (i.e. amount) of exercise would be correlated with reduced fasting and postprandial arterial stiffness in obese adults with prediabetes. After randomization, 31 adults (age 61.4 ± 8.3 years, body mass index 32.1 ± 5.4 kg m-2 ) with prediabetes performed supervised continuous (CONT; n = 17; 70% of peak heart rate) or interval (INT; n = 14; 3 min at 50% of peak heart rate and 3 min at 90% of peak heart rate) cycling training for 60 min day-1 over 2 weeks. The amount of exercise was calculated using regression equations derived from oxygen uptake (V ̇ O 2 ) and heart rate. Arterial stiffness [augmentation index (AI) and cartoid-femoral pulse wave velocity], insulin and glucose were determined during a 180 min 75 g oral glucose tolerance test (OGTT) and analysed by the total area under the curve (tAUC) pre- versus post-training. The simple index of insulin sensitivity, (SIIS )OGTT, was calculated; aerobic fitness (peakV ̇ O 2 ) and body mass were also assessed. Short-term training had no effect on weight but did improve peakV ̇ O 2 (P = 0.003), glucose tAUC180min (P = 0.01) and insulin sensitivity (P = 0.002), independent of intensity. The CONT and INT exercise significantly reduced AI 2 h postprandial (P = 0.008) and tAUC180min (P = 0.03). Reductions in fasted AI were related to exercise dose (trend: r = -0.37, P = 0.055). Increased peakV ̇ O 2 was linked to reduced fasted (r = -0.47, P = 0.01) and tAUC180min AI (r = -0.39, P = 0.05). Decreased AI tAUC180min was correlated with increased insulin sensitivity (r = -0.50, P = 0.009). Short-term CONT and INT training reduced postprandial arterial stiffness comparably in adults with prediabetes.

Early vascular parameters in the micro- and macrocirculation in type 2 diabetes

BACKGROUND

Diabetes converts from a metabolic disorder into a predominantly vascular disease, once its duration extends over several years or/and when additional cardiovascular risk factors such as hypertension coexist. In a cross-sectional analysis we analyzed various vascular parameters in the renal, retinal and systemic circulation, with the goal to identify which vascular parameter of early organ damage is the earliest that can be clinically detected.

METHODS

In 111 patients with type 2 diabetes (T2DM) (off any anti-diabetic medication for at least 4 weeks) and 54 subjects without T2DM we compared various parameters of early vascular remodeling in the same patient: urinary albumin creatinine ratio ([UACR], early morning spot urine) and estimated glomerular filtration rate (eGFR), retinal capillary flow (RCF) and intercapillary distance (ICD) as parameters of capillary rarefaction, wall-to-lumen ratio (WLR) of the retinal arterioles [all assessed by Scanning Laser Doppler Flowmetry], and central systolic pressure (cSBP) and central pulse pressure (cPP) [measured by pulse wave analysis, Syphygmocor] both reflecting vascular stiffness of large arteries.

RESULTS

Compared to subjects without T2DM, patients with T2DM (diabetes duration: median 48 months, interquartile range 24-88 months) were older (59.8 ± 7.3 vs 43.4 ± 12.9 years, p < 0.001), more females (33.3 vs 20.4%, p < 0.001), but 24-h systolic and diastolic blood pressure did not differ between the two groups. The analysis adjusted for age, gender and cardiovascular risk factors revealed that ICD (23.9 ± 5.1 vs 20.8 ± 3.5 µm, p value = 0.001) and cPP (41.8 ± 11.7 vs 34.8 ± 10.6 mmHg, p value < 0.001) were significantly higher and eGFR (91.7 ± 9.9 vs 95.9 ± 17.3 ml/min/1.73 m², p value < 0.001) was significantly lower in patients with T2DM than in subjects without T2DM.

CONCLUSION

These data suggest that at similar blood pressure capillary rarefaction in the retinal circulation (ICD), decreased eGFR in the renal circulation and increased central pulse pressure (cPP) of large arteries are earlier detectable than other vascular remodeling parameters of the micro- (WLR, RCF, UACR) and macrocirculation (cSBP) in patients with T2DM. Trial registration Trial registration number: NCT02471963, Date of registration: June 15, 2015, retrospectively registered; Trial registration number: NCT01319357, Date of registration: March 21, 2011, retrospectively registered; Trial registration number: NCT02383238, Date of registration: March 9, 2015, retrospectively registered; Trial registration number: NCT00152698, Date of registration: September 9, 2005, prospectively registered; Trial registration number: NCT00136188, Date of registration: August 26, 2005, prospectively registered.