Mast cell degranulation and de novo histamine formation contribute to sustained postexercise vasodilation in humans

A Wearable Electrochemical Sensor Based on a Molecularly Imprinted Polymer Integrated with a Copper Benzene-1,3,5-Tricarboxylate Metal-Organic Framework for the On-Body Monitoring of Cortisol in Sweat

Owing to their potential to transform traditional medical diagnostics and health monitoring, wearable biosensors have become an alternative evolutionary technology in the field of medical care. However, it is still necessary to overcome some key technique challenges, such as the selectivity, sensitivity, and stability of biometric identification. Herein, a novel, wearable electrochemical sensor based on a molecularly imprinted polymer (MIP) integrated with a copper benzene-1,3,5-tricarboxylate metal-organic framework (MOF) was designed for the detection of stress through the on-body monitoring of cortisol in sweat. The MOF was used as the substrate for MIP deposition to enhance the stability and sensitivity of the sensor. The sensor consisted of two layers, with a microfluidic layer as the top layer for spontaneous sweating and a modified electrode as the bottom layer for sensing. The sensor measured cortisol levels by detecting the current change that occurred when the target molecules bound to the imprinted cavities, using Prussian blue nanoparticles embedded in the MIP framework as the REDOX probe. The proposed sensor exhibited a linear detection range of 0.01-1000 nM with a detection limit of 0.0027 nM, and favorable specificity over other analogies. This facile anti-body free sensor showed excellent stability, and can be successfully applied for in situ cortisol monitoring.

History of Multiple Allergies and Gradual Onset Running-Related Injuries in Distance Runners: SAFER XXXV

OBJECTIVE

To determine if any gradual onset running-related injury (GORRI) was associated with any allergies, multiple allergies (allergies to animals, plants, medication), and allergy medication use.

DESIGN

Cross-sectional descriptive study.

SETTING

Two Oceans Marathons (56 km, 21.1 km), South Africa.

PARTICIPANTS

A total of 76 654 race entrants (2012-2015).

INDEPENDENT VARIABLES

The prevalence (%) and prevalence ratios (PR; 95% confidence intervals) for history of (1) any allergies, (2) multiple allergies to broad categories of allergens (animal material, plant material, allergies to medication, and other allergies), and (3) allergy medication use.

MAIN OUTCOME MEASURES

Using a compulsory online screening questionnaire, the outcome was a history of any GORRIs, and subcategories of GORRIs (muscle, tendon) in the past 12 months and history of GORRIs (and subtypes of GORRIs) were reported.

RESULTS

In 68 258 records with injury and allergy data, the following were significantly associated with reporting any GORRIs: a history of any allergy (PR = 2.2; P < 0.0001), a history of allergies to broad categories of allergens (animal, plant, medication allergy, other) (P < 0.0001), and the use of allergy medication (P < 0.0001). A history of any allergies (PR = 2.4; P < 0.0001), all broad categories of allergies, and allergy medication use were significantly associated with muscle (P < 0.0001) and tendon injuries (P < 0.0001). The risk of reporting a GORRI increased as the number of reported categories of allergies increased (P < 0.0001).

CONCLUSIONS

A novel finding was the cumulative risk effect with a history of multiple allergies. Further studies should aim to determine the underlying mechanism relating allergies and GORRIs.

Bioactive nanomaterials kickstart early repair processes and potentiate temporally modulated healing of healthy and diabetic wounds

Slow-healing and chronic wounds represent a major global economic and medical burden, and there is significant unmet need for novel therapies which act to both accelerate wound closure and enhance biomechanical recovery of the skin. Here, we report a new approach in which bioactives that augment early stages of wound healing can kickstart and engender effective wound closure in healthy and diabetic, obese animals, and set the stage for subsequent tissue repair processes. We demonstrate that a nanomaterial dressing made of silk fibroin and gold nanorods (GNR) stimulates a pro-neutrophilic, innate immune, and controlled inflammatory wound transcriptomic response. Further, Silk-GNR, lasered into the wound bed, in combination with exogeneous histamine, accelerates early-stage processes in tissue repair leading to effective wound closure. Silk-GNR and histamine enhanced biomechanical recovery of skin, increased transient neoangiogenesis, myofibroblast activation, epithelial-to-mesenchymal transition (EMT) of keratinocytes and a pro-resolving neutrophilic immune response, which are hitherto unknown activities for these bioactives. Predictive and temporally coordinated delivery of growth factor nanoparticles that modulate later stages of tissue repair further accelerated wound closure in healthy and diabetic, obese animals. Our approach of kickstarting healing by delivering the "right bioactive at the right time" stimulates a multifactorial, pro-reparative response by augmenting endogenous healing and immunoregulatory mechanisms and highlights new targets to promote tissue repair.

Effect of histamine-receptor antagonism on the circulating inflammatory cell and cytokine response to exercise: A pilot study

The purpose of this study was to gain insight into histamine's role in the exercise inflammatory response and recovery from exercise. To explore this, young healthy participants (n = 12) performed 300 eccentric leg extensions under control (Placebo) versus histamine H1 and H2 receptor antagonism (Blockade) in a randomized cross-over study. Circulating leukocytes and cytokines were measured for 72 h after exercise. Circulating leukocytes were elevated at 6 and 12 h after exercise (p < 0.05) with the peak response being a 44.1 ± 11.7% increase with Blockade versus 13.7 ± 6.6% with Placebo (both p < 0.05 vs. baseline, but also p < 0.05 between Blockade and Placebo). Of the cytokines that were measured, only MCP-1 was elevated following exercise. The response at 6 h post-exercise was a 104.0 ± 72.5% increase with Blockade versus 93.1 ± 41.9% with Placebo (both p < 0.05 vs. baseline, p = 0.82 between Blockade and Placebo). The main findings of the present investigation were that taking combined histamine H1 and H2 receptor antagonists augmented the magnitude but not the duration of the increase of circulating immune cells following exercise. This suggests histamine is not only exerting a local influence within the skeletal muscle but that it may influence the systemic inflammatory patterns.

Cyclooxygenase inhibition does not blunt thermal hyperemia in skeletal muscle of humans

Acute heat exposure increases skeletal muscle blood flow in humans. However, the mechanisms mediating this hyperemic response remain unknown. The cyclooxygenase pathway is active in skeletal muscle, is heat sensitive, and contributes to cutaneous thermal hyperemia in young healthy humans. Therefore, the purpose of this study was to test the hypothesis that cyclooxygenase inhibition would attenuate blood flow in the vastus lateralis muscle during localized heating. Twelve participants (6 women) were studied on two separate occasions: 1) time control (i.e., no ibuprofen); and 2) ingestion of 800 mg ibuprofen, a nonselective cyclooxygenase inhibitor. Experiments were randomized, counter-balanced, and separated by at least 10 days. Pulsed short-wave diathermy was used to induce unilateral deep heating of the vastus lateralis for 90 min, whereas the contralateral leg served as a thermoneutral control. Microdialysis was utilized to bypass the cutaneous circulation and directly measure local blood flow in the vastus lateralis muscle of each leg via the ethanol washout technique. Heat exposure increased muscle temperature and local blood flow (both P < 0.01 vs. baseline). However, the thermal hyperemic response did not differ between control and ibuprofen conditions (P ≥ 0.2). Muscle temperature slightly decreased for the thermoneutral leg (P < 0.01 vs. baseline), yet local blood flow remained relatively unchanged across time for control and ibuprofen conditions (both P ≥ 0.7). Taken together, our data suggest that inhibition of cyclooxygenase-derived vasodilator prostanoids does not blunt thermal hyperemia in skeletal muscle of young healthy humans.NEW & NOTEWORTHY Acute heat exposure increases skeletal muscle blood flow in humans. However, the mechanisms mediating this hyperemic response remain unknown. Using a pharmacological approach combined with microdialysis, we found that thermal hyperemia in the vastus lateralis muscle was well maintained despite the successful inhibition of cyclooxygenase. Our results suggest that cyclooxygenase-derived vasodilator prostanoids do not contribute to thermal hyperemia in skeletal muscle of young healthy humans.

Heatstroke-induced acute kidney injury and the innate immune system

Heatstroke can cause multiple organ failure and systemic inflammatory response syndrome as the body temperature rises beyond the body's ability to regulate temperature in a hot environment. Previous studies have indicated that heatstroke-induced acute kidney injury (AKI) can lead to chronic kidney disease. Therefore, there is an urgent need to elucidate the mechanism of heatstroke-induced AKI and to establish methods for its prevention and treatment. Recent reports have revealed that innate immunity, including neutrophils, macrophages, lymphocytes, and mast cells, is deeply involved in heat-induced AKI. In this review, we will discuss the roles of each immune cell in heat-induced renal injury and their potential therapeutic use.

Transcutaneous delivery of sodium bicarbonate increases intramuscular pH

Introduction: Oral bicarbonate loading improves the buffering of metabolic acidosis and may improve exercise performance but can also result in gastric distress. Momentous' PR Lotion contains a novel composition intended to provide a transdermal delivery vehicle for sodium bicarbonate which could allow the same ergogenic effect without the gastric distress. The present study explored the effect of transdermal delivery of sodium bicarbonate in a resting condition. Methods: We measured the pH from intramuscular dialysate, via microdialysis, of the vastus lateralis during a 2 h application of PR Lotion (40 g of lotion per leg) in 9 subjects (3 women, 6 men). Venous blood samples were obtained for serum pH before and after application. A placebo time control was also performed in 4 subjects (2 women, 2 men). We hypothesized that PR Lotion application would increase pH of intramuscular dialysate. Results: PR Lotion resulted in a rise in pH of 0.13 ± 0.04 units (p < 0.05), which translates to a 28% reduction in [H⁺]. Increases in serum pH were smaller (∼9%) yet consistent (p < 0.05). In contrast, placebo time control pH tended to decrease (p = 0.08). The effect of PR Lotion on pH tended to correlate with the dose per kg body weight of each individual (r = 0.70, p = 0.08). Conclusion: These observations support the idea of transdermal bicarbonate delivery impacting pH buffering both systemically and intramuscularly. Further work investigating these potential benefits in an exercising model would be critical to establishing PR Lotion's utility as an ergogenic aid.

Dysregulation of Amino Acid, Lipid, and Acylpyruvate Metabolism in Idiopathic Intracranial Hypertension: A Non-targeted Case Control and Longitudinal Metabolomic Study

Background: Idiopathic intracranial hypertension (IIH) is characterized by increased intracranial pressure occurring predominantly in women with obesity. The pathogenesis is not understood. We have applied untargeted metabolomic analysis using ultrahigh-performance liquid chromatography-mass spectrometry to characterize the cerebrospinal fluid (CSF) and serum in IIH compared to control subjects. Methods and findings: Samples were collected from IIH patients (n = 66) with active disease at baseline and again at 12 months following therapeutic weight loss. Control samples were collected from gender- and weight-matched healthy controls (n = 20). We identified annotated metabolites in CSF, formylpyruvate and maleylpyruvate/fumarylpyruvate, which were present at lower concentrations in IIH compared to control subjects and returned to values observed in controls following weight loss. These metabolites showed the opposite trend in serum at baseline. Multiple amino acid metabolic pathways and lipid classes were perturbed in serum and CSF in IIH alone. Serum lipid metabolite pathways were significantly increased in IIH. Conclusions: We observed a number of differential metabolic pathways related to amino acid, lipid, and acylpyruvate metabolism, in IIH compared to controls. These pathways were associated with clinical measures and normalized with disease remission. Perturbation of these metabolic pathways provides initial understanding of disease dysregulation in IIH.

Beyond cardiomyocytes: Cellular diversity in the heart's response to exercise

Cardiomyocytes comprise ∼70% to 85% of the total volume of the adult mammalian heart but only about 25% to 35% of its total number of cells. Advances in single cell and single nuclei RNA sequencing have greatly facilitated investigation into and increased appreciation of the potential functions of non-cardiomyocytes in the heart. While much of this work has focused on the relationship between non-cardiomyocytes, disease, and the heart's response to pathological stress, it will also be important to understand the roles that these cells play in the healthy heart, cardiac homeostasis, and the response to physiological stress such as exercise. The present review summarizes recent research highlighting dynamic changes in non-cardiomyocytes in response to the physiological stress of exercise. Of particular interest are changes in fibrotic pathways, the cardiac vasculature, and immune or inflammatory cells. In many instances, limited data are available about how specific lineages change in response to exercise or whether the changes observed are functionally important, underscoring the need for further research.

Metabolome and transcriptome analysis on muscle of sporadic inclusion body myositis

Objective

Methods

Results

Interpretation

Physical Activity and Hypertension

Hypertension and physical inactivity are leading causes of premature mortality. While both are modifiable risk factors for cardiovascular disease, their prevalence remains high. As populations grow older, they are more likely to develop hypertension and to become less physically active. Scientific advances have contributed to understanding of how physical activity improves blood pressure and the clinically relevant ambulatory blood pressure, but this is not reflected in hypertension guidelines for clinical management of hypertension. The aim of this paper is to clearly present up to date knowledge from scientific studies that underpin the role of physical activity in hypertension management. Longitudinal studies in this review demonstrate a protective effect of higher physical activity levels as well as higher levels of cardiorespiratory fitness. Interventional studies report improvements in blood pressure associated with aerobic, resistance and concurrent exercise; the improvements in some studies were greatest among participant groups with established hypertensions; the effect was observed for groups with treatment-resistant hypertension also, a clinically important subgroup. The most recent research provides evidence for the synergy between physical activity and pharmacotherapy for the treatment of hypertension, providing an opportunity for clinicians to promote physical activity as an adjunctive treatment for hypertension as well as a preventative strategy. This review critiques the evidence and summarises the most up to date literature in the field of physical activity and hypertension.

Acute heat exposure improves microvascular function in skeletal muscle of aged adults

Acute heat exposure improves microvascular function in aged adults as assessed using reactive hyperemia. The cutaneous and skeletal muscle microcirculations are thought to contribute to this response, but this has never been confirmed due to the methodological challenges associated with differentiating blood flow between these vascular beds. We hypothesized that acute hot water immersion would improve endothelial-dependent, but not endothelial-independent vasodilation in the microcirculation of the vastus lateralis muscle in healthy aged adults. Participants (70 ± 5 yr) were immersed for 60 min in thermoneutral (36°C) or hot (40°C) water. Ninety minutes following immersion, skeletal muscle microdialysis was used to bypass the cutaneous circulation and directly assess endothelial-dependent and endothelial-independent vasodilation by measuring the local hyperemic response to graded infusions of acetylcholine (ACh, 27.5 and 55.0 mM) and sodium nitroprusside (SNP, 21 and 42 mM), respectively. The hyperemic response to 27.5 mM ACh did not differ between thermal conditions (P = 0.9). However, the hyperemic response to 55.0 mM ACh was increased with prior hot water immersion (thermoneutral immersion, 43.9 ± 23.2 mL/min/100 g vs. hot water immersion, 66.5 ± 25.5 mL/min/100 g; P < 0.01). Similarly, the hyperemic response to 21 mM SNP did not differ between thermal conditions (P = 0.3) but was increased following hot water immersion with the infusion of 42 mM SNP (thermoneutral immersion, 48.8 ± 25.6 mL/min/100 g vs. hot water immersion, 90.7 ± 53.5 mL/min/100 g; P < 0.01). These data suggest that acute heat exposure improves microvascular function in skeletal muscle of aged humans.NEW & NOTEWORTHY Acute heat exposure improves microvascular function in aged adults as assessed using reactive hyperemia. The cutaneous and skeletal muscle microcirculations are thought to contribute to this response, but this has never been confirmed due to the methodological challenges associated with differentiating blood flow between these vascular beds. Using the microdialysis technique to bypass the cutaneous circulation, we demonstrated that heat exposure improves endothelial-dependent and endothelial-independent vasodilation in the microcirculation of skeletal muscle in aged humans.

The effect of local passive heating on skeletal muscle histamine concentration: implications for exercise-induced histamine release

Aerobic exercise induces mast cell degranulation and increases histamine formation by histidine decarboxylase, resulting in an ∼150% increase in intramuscular histamine. The purpose of this study was to determine if the increase in skeletal muscle temperature associated with exercise is sufficient to explain this histamine response. Specifically, we hypothesized that local passive heating that mimics the magnitude and time course of changes in skeletal muscle temperature observed during exercise would result in increased intramuscular histamine concentrations comparable to exercising values. Seven subjects participated in the main study in which pulsed short-wave diathermy was used to passively raise the temperature of the vastus lateralis over 60 min. Heating increased intramuscular temperature from 32.6°C [95% confidence interval (CI) 32.0°C to 33.2°C] to 38.9°C (38.7°C to 39.2°C) (P < 0.05) and increased intramuscular histamine concentration from 2.14 ng/mL (1.92 to 2.36 ng/mL) to 2.97 ng/mL (2.57 to 3.36 ng/mL) (P < 0.05), an increase of 41%. In a follow-up in vitro experiment using human-derived cultured mast cells, heating to comparable temperatures did not activate mast cell degranulation. Therefore, it appears that exercise-associated changes in skeletal muscle temperature are sufficient to generate elevations in intramuscular histamine concentration. However, this thermal effect is most likely due to changes in de novo histamine formation via histidine decarboxylase and not due to degranulation of mast cells. In conclusion, physiologically relevant increases in skeletal muscle temperature explain part, but not all, of the histamine response to aerobic exercise. This thermal effect may be important in generating positive adaptations to exercise training.NEW & NOTEWORTHY The "exercise signal" that triggers histamine release within active skeletal muscle during aerobic exercise is unknown. By mimicking the magnitude and time course of increasing skeletal muscle temperature observed during aerobic exercise, we demonstrate that part of the exercise-induced rise in histamine is explained by a thermal effect, with in vitro experiments suggesting this is most likely via de novo histamine formation. This thermal effect may be important in generating positive adaptations to exercise training.

The Role of the Skeletal Muscle Secretome in Mediating Endurance and Resistance Training Adaptations

Exercise, in the form of endurance or resistance training, leads to specific molecular and cellular adaptions not only in skeletal muscles, but also in many other organs such as the brain, liver, fat or bone. In addition to direct effects of exercise on these organs, the production and release of a plethora of different signaling molecules from skeletal muscle are a centerpiece of systemic plasticity. Most studies have so far focused on the regulation and function of such myokines in acute exercise bouts. In contrast, the secretome of long-term training adaptation remains less well understood, and the contribution of non-myokine factors, including metabolites, enzymes, microRNAs or mitochondrial DNA transported in extracellular vesicles or by other means, is underappreciated. In this review, we therefore provide an overview on the current knowledge of endurance and resistance exercise-induced factors of the skeletal muscle secretome that mediate muscular and systemic adaptations to long-term training. Targeting these factors and leveraging their functions could not only have broad implications for athletic performance, but also for the prevention and therapy in diseased and elderly populations.

Pulsatile load and wasted pressure effort are reduced following an acute bout of aerobic exercise

Following aerobic exercise, sustained vasodilation and concomitant reductions in total peripheral resistance (TPR) result in a reduction in blood pressure that is maintained for two or more hours. However, the time course for postexercise changes in reflected wave amplitude and other indices of pulsatile load on the left ventricle have not been thoroughly described. Therefore, we tested the hypothesis that reflected wave amplitude is reduced beyond an hour after cycling at 60% V̇o_2peak for 60 min. Aortic pressure waveforms were derived in 14 healthy adults (7 men, 7 women; 26 ± 3 yr) from radial pulse waves acquired via high-fidelity applanation tonometry at baseline and every 20 min for 120 min postexercise. Concurrently, left ventricle outflow velocities were acquired via Doppler echocardiography and pressure-flow analyses were performed. Aortic characteristic impedance (Zc), forward (Pf) and backward (Pb) pulse wave amplitude, reflected wave travel time (RWTT), and wasted pressure effort (WPE) were derived. Reductions in aortic blood pressure, Zc, Pf, and Pb were all sustained postexercise whereas increases in RWTT emerged from 60 to 100 min post exercise (all P < 0.05). WPE was reduced by ∼40% from 40 to 100 min post exercise (all P < 0.02). Stepwise multiple regression analysis revealed that the peak ΔWPE was associated with ΔRWTT (β = -0.57, P = 0.003) and ΔPb (β = 0.52, P = 0.006), but not Δcardiac output, ΔTPR, ΔZc, or ΔPf. These results suggest that changes in pulsatile hemodynamics are sustained for ≥100 min following moderate intensity aerobic exercise. Moreover, decreased and delayed reflected pressure waves are associated with decreased left ventricular wasted effort after exercise.NEW & NOTEWORTHY We demonstrate that pulsatile load on the left ventricle is diminished following 60 min of moderate intensity aerobic exercise. During recovery from exercise, the amplitude of the forward and backward traveling pressure waves are attenuated and the arrival of reflected waves is delayed. Thus, the work imposed upon the left ventricle by reflected pressure waves, wasted pressure effort, is decreased after exercise.

Histamine, mast cell tryptase and post-exercise hypotension in healthy and collapsed marathon runners

PURPOSE

Heat stress exacerbates post-exercise hypotension (PEH) and cardiovascular disturbances from elevated body temperature may contribute to exertion-related incapacity. Mast cell degranulation and muscle mass are possible modifiers, though these hypotheses lack practical evidence. This study had three aims: (1) to characterise pre-post-responses in histamine and mast cell tryptase (MCT), (2) to investigate relationships between whole body muscle mass (WBMM) and changes in blood pressure post-marathon, (3) to identify any differences in incapacitated runners.

METHODS

24 recreational runners were recruited and successfully completed the 2019 Brighton Marathon (COMPLETION). WBMM was measured at baseline. A further eight participants were recruited from incapacitated runners (COLLAPSE). Histamine, MCT, blood pressure, heart rate, body temperature and echocardiographic measures were taken before and after exercise (COMPLETION) and upon incapacitation (COLLAPSE).

RESULTS

In completion, MCT increased by nearly 50% from baseline (p = 0.0049), whereas histamine and body temperature did not vary (p > 0.946). Systolic (SBP), diastolic (DBP) and mean (MAP) arterial blood pressures and systemic vascular resistance (SVR) declined (p < 0.019). WBMM negatively correlated with Δ SBP (r = - 0.43, p = 0.046). For collapse versus completion, there were significant elevations in MCT (1.77 ± 0.25 μg/L vs 1.18 ± 0.43 μg/L, p = 0.001) and body temperature (39.8 ± 1.3 °C vs 36.2 ± 0.8 °C, p < 0.0001) with a non-significant rise in histamine (9.6 ± 17.9 μg/L vs 13.7 ± 33.9 μg/L, p = 0.107) and significantly lower MAP, DBP and SVR (p < 0.033).

CONCLUSION

These data support the hypothesis that mast cell degranulation is a vasodilatory mechanism underlying PEH and exercise associated collapse. The magnitude of PEH is inversely proportional to the muscle mass and enhanced by concomitant body heating.

The acute and chronic effects of high-intensity exercise in hypoxia on blood pressure and post-exercise hypotension: A randomized cross-over trial

BACKGROUND

Acute exercise leads to an immediate drop in blood pressure (BP), also called post-exercise hypotension (PEH). Exercise in hypoxia is related to additional vasodilation, potentially contributing to more profound PEH. Therefore, we investigated the impact of hypoxia versus normoxia on the magnitude of PEH. Second, we examined whether these changes in PEH relate to the BP-lowering effects of 12-week exercise training under hypoxia.

METHODS

In this prospective study, 21 healthy individuals (age 22.2 ± 3.0 years, 14 male) performed a 45-minute high-intensity running exercise on 2 different days in a random order, under hypoxia (fraction of inspired oxygen 14.5%) and normoxia (fraction of inspired oxygen 20.9%). BP was examined pre-exercise (t = 0) and at t = 15, t = 30, t = 45, and t = 60 minutes post-exercise. Afterward, subjects took part in a 12-week hypoxic running exercise training program. Resting BP was measured before and after the 12-week training program.

RESULTS

Acute exercise induced a significant decrease in systolic BP (systolic blood pressure [SBP], P = .001), but not in diastolic BP (diastolic blood pressure [DBP], P = .113). No significant differences were observed in post-exercise BP between hypoxic and normoxic conditions (SBP, P = .324 and DBP, P = .204). Post-exercise changes in SBP, DBP, and mean arterial pressure significantly correlated to the 12-week exercise training-induced changes in SBP (r = 0.557, P = .001), DBP (r = 0.615, P < .001), and mean arterial pressure (r = 0.458, P = .011).

CONCLUSION

Our findings show that hypoxia does not alter the magnitude of PEH in healthy individuals, whilst PEH relates to the BP-lowering effects of exercise. These data highlight the strong link between acute and chronic changes in BP.

Postural Tachycardia Syndrome in Children and Adolescents: Pathophysiology and Clinical Management

Postural tachycardia syndrome (POTS), characterized by chronic (≥6 months) orthostatic intolerance symptoms with a sustained and excessive heart rate increase while standing without postural hypotension, is common in children and adolescents. Despite the unclear pathogenesis of POTS, the present opinion is that POTS is a heterogeneous and multifactorial disorder that includes altered central blood volume, abnormal autonomic reflexes, "hyperadrenergic" status, damaged skeletal muscle pump activity, abnormal local vascular tension and vasoactive factor release, mast cell activation, iron insufficiency, and autoimmune dysfunction. A number of pediatric POTS patients are affected by more than one of these pathophysiological mechanisms. Therefore, individualized treatment strategies are initiated in the management of POTS, including basal non-pharmacological approaches (e.g., health education, the avoidance of triggers, exercise, or supplementation with water and salt) and special pharmacological therapies (e.g., oral rehydration salts, midodrine hydrochloride, and metoprolol). As such, the recent progress in the pathogenesis, management strategies, and therapeutic response predictors of pediatric POTS are reviewed here.

Effect of histamine-receptor antagonism on leg blood flow during exercise

Histamine mediates vasodilation during inflammatory and immune responses, as well as following endurance exercise. During exercise, intramuscular histamine concentration increases, and its production, appears related to exercise intensity and duration. However, whether histamine contributes to exercise hyperemia and promotes exercise blood flow in an intensity- or duration-dependent pattern is unknown. The purpose of this study was to compare leg blood flow across a range of exercise intensities, before and after prolonged exercise, with and without histamine-receptor antagonism. It was hypothesized that combined oral histamine H₁/H₂-receptor antagonism would decrease leg blood flow, and the effect would be greater at higher intensities and following prolonged exercise. Sixteen (7F, 9M) volunteers performed single-leg knee-extension exercise after consuming either placebo or combined histamine H₁/H₂-receptor antagonists (Blockade). Exercise consisted of two graded protocols at 20, 40, 60, and 80% of peak power, separated by 60 min of knee-extension exercise at 60% of peak power. Femoral artery blood flow was measured by ultrasonography. Femoral artery blood flow increased with exercise intensity up to 2,660 ± 97 mL/min at 80% of peak power during Placebo (P < 0.05). Blood flow was further elevated with Blockade to 2,836 ± 124 mL/min (P < 0.05) at 80% peak power (9.1 ± 4.8% higher than placebo). These patterns were not affected by prolonged exercise (P = 0.13). On average, femoral blood flow during prolonged exercise was 12.7 ± 2.8% higher with Blockade vs. Placebo (P < 0.05). Contrary to the hypothesis, these results suggest that histamine receptor antagonism during exercise, regardless of intensity or duration, increases leg blood flow measured by ultrasonography.NEW & NOTEWORTHY Leg blood flow during exercise was increased by taking antihistamines, which block the receptors for histamine, a molecule often associated with inflammatory and immune responses. The elevated blood flow occurred over exercise intensities ranging from 20 to 80% of peak capacity and during exercise of 60 min duration. These results suggest that exercise-induced elevations in histamine concentrations are involved in novel, poorly understood, and perhaps complex ways in the exercise response.

Amelioration of Large Bile Duct Damage by Histamine-2 Receptor Vivo-Morpholino Treatment

Histamine binds to one of the four G-protein-coupled receptors expressed by large cholangiocytes and increases large cholangiocyte proliferation via histamine-2 receptor (H2HR), which is increased in patients with primary sclerosing cholangitis (PSC). Ranitidine decreases liver damage in Mdr2^-/- (ATP binding cassette subfamily B member 4 null) mice. We targeted hepatic H2HR in Mdr2^-/- mice using vivo-morpholino. Wild-type and Mdr2^-/- mice were treated with mismatch or H2HR vivo-morpholino by tail vein injection for 1 week. Liver damage, mast cell (MC) activation, biliary H2HR, and histamine serum levels were studied. MC markers were determined by quantitative real-time PCR for chymase and c-kit. Intrahepatic biliary mass was detected by cytokeratin-19 and F4/80 to evaluate inflammation. Biliary senescence was determined by immunofluorescence and senescence-associated β-galactosidase staining. Hepatic fibrosis was evaluated by staining for desmin, Sirius Red/Fast Green, and vimentin. Immunofluorescence for transforming growth factor-β₁, vascular endothelial growth factor-A/C, and cAMP/ERK expression was performed. Transforming growth factor-β₁ and vascular endothelial growth factor-A secretion was measured in serum and/or cholangiocyte supernatant. Treatment with H2HR vivo-morpholino in Mdr2^-/--mice decreased hepatic damage; H2HR protein expression and MC presence or activation; large intrahepatic bile duct mass, inflammation and senescence; and fibrosis, angiogenesis, and cAMP/phospho-ERK expression. Inhibition of H2HR signaling ameliorates large ductal PSC-induced damage. The H2HR axis may be targeted in treating PSC.

Inhibitory function of Shikonin on MRGPRX2-mediated pseudo-allergic reactions induced by the secretagogue

BACKGROUND

Mast cells (MCs) are crucial effectors in allergic disorders by secreting inflammatory mediators. The Mas-related G-protein-coupled receptor X2 (Mrgprx2) was shown to have a key role in IgE-independent allergic reactions. Therefore, potential drug candidates that directly target Mrgprx2 could be used to treat pseudo-allergic diseases. Shikonin, an active ingredient derived from Lithospermum erythrorhizon Sieb. et Zucc has been used for its anti-inflammatory properties since ancient China.

PURPOSE

To investigate the inhibitory effects of Shikonin on IgE-independent allergy both in vitro and in vivo, as well as the mechanism underlying its effects.

METHODS/STUDY DESIGNS

The anti-anaphylactoid activity of Shikonin was evaluated in PCA and systemic anaphylaxis models, Calcium imaging was used to assess intracellular Ca²⁺ mobilization. The release of cytokines and chemokines was measured using enzyme immunoassay kits. Western blot analysis was conducted to investigate the molecules of PLCγ-PKC-IP3 signaling pathway. The analytical method of surface plasmon resonance was employed to study the interaction between Shikonin and potential target protein Mrgprx2.

RESULTS

Shikonin can suppress compound 48/80 (C48/80)-induced PCA, active systemic anaphylaxis, and MCs degranulation in mice in a dose-dependent manner. In addition, Shikonin reduced C48/80-induced calcium flux and suppressed LAD2 cell degranulation via PLCγ-PKC-IP3 signaling pathway. Moreover, Shikonin was found to inhibit C48/80-induced Mrgprx2 expression in HEK cells, displaying specific interactions with the Mrgprx2 protein.

CONCLUSION

Shikonin could be a potential antagonist of Mrgprx2, thereby inhibiting pseudo-allergic reactions through Ca²⁺ mobilization.

Besides Photothermal Effects, Low-Level CO2 Laser Irradiation Can Potentiate Skin Microcirculation Through Photobiomodulation Mechanisms

Background: Improvement of microcirculation is one of the important mechanisms of low-level laser therapy (LLLT) to treat some diseases such as wound healing. Most previous studies have been carried out with multiple lasers other than the 10,600-nm CO₂ laser. Recently, the CO₂ laser has been used not only as a tool for excision of soft tissues but also for therapeutic applications. Objective: To study whether low-level CO₂ laser irradiation can influence microcirculation and further explore the underlying mechanisms. Methods: Seventy-milliwatt (70-mW) CO₂ lasers irradiated the forearms of 12 participants and skin blood perfusion (SkBP) was measured with a laser speckle imager. The thermal effect of irradiation was evaluated by measuring the irradiated skin in vivo and the exposed cell suspensions in vitro. Extracellular adenosine triphosphate (eATP) of the human mast cell line (HMC-1) is assessed by luciferin-luciferase assay to explore the potential mechanisms. Results: Irradiation caused dose-dependent increase in SkBP. At a medium dose of 262 J/cm², SkBP reached its maximum value at 195.8% ± 18.6% of the baseline (n = 12, p < 0.01). Such laser irradiation had a mild thermal effect, heating local skin temperature (SkT) by 6.1°C ± 0.3°C (n = 10) and warming cell suspensions by 4.5°C ± 0.8°C (n = 6). Irradiation dose-dependently lowered eATP levels of HMC-1 cells in vitro. At a medium dose of 262 J/cm², eATP levels declined to the minimum at 74.8% ± 5.5% of the baseline (n = 12, p < 0.01). This downregulation effect could be significantly inhibited by 100-μM ARL67156, a nonspecific ecto-ATPase inhibitor. On the contrary, heating itself slightly raised the level of eATP. Conclusions: Low-level CO₂ laser irradiation can improve microcirculation. Besides the thermal effect, regulation of extravascular eATP by the photobiomodulation mechanism may be involved. This implies that CO₂ lasers might be used in LLLT.

Histamine-Receptor Antagonists Slow 10-km Cycling Performance in Competitive Cyclists

Histamine is released within skeletal muscle during exercise. In humans, antihistamines have no effect on speed, power output, or time-to-completion of short-duration high-intensity exercise. In mice, blocking histamine's actions decreases speed and duration of endurance tasks. It is unknown if these opposing outcomes are the result of differences in histamine's actions between species or are related to duration and/or intensity of exercise, as blocking histamine during endurance exercise has not been examined in humans.

PURPOSE

Determine the effects of histamine-receptor antagonism on cycling time trial performance in humans, with and without a preceding bout of sustained steady-state exercise.

METHODS

Eleven (3F) competitive cyclists performed six 10-km time trials on separate days. The first two time trials served as familiarization. The next four time trials were performed in randomized-block order, where two were preceded by 120 min of seated rest (rest) and two by 120 min of cycling exercise (Exercise) at 50% V˙O2peak. Within each block, subjects consumed either combined histamine H1 and H2 receptor antagonists (Blockade) or Placebo, before the start of the 120-min Rest/Exercise.

RESULTS

Blockade had no discernible effects on hemodynamic or metabolic variables during Rest or Exercise. However, Blockade increased time-to-completion of the 10-km time trial compared with Placebo (+10.5 ± 3.7 s, P < 0.05). Slowing from placebo to blockade was not different between rest (+8.7 ± 5.2 s) and Exercise (+12.3 ± 5.8 s, P = 0.716).

CONCLUSIONS

Exercise-related histaminergic signaling appears inherent to endurance exercise and may play a role in facilitating optimal function during high-intensity endurance exercise.

Postural orthostatic tachycardia syndrome and the potential role of mast cell activation

Though a sizeable amount of data connects mast cell activity to the neurologic system, less is known about the true clinical implications of this relationship. Even less is understood about treatment strategies in those with both allergic and neurologic complaints. This is particularly true in postural orthostatic tachycardia syndrome (POTS), a common type of dysautonomia, where patients are burdened by symptoms of orthostatic cerebral hypoperfusion and several other comorbidities that are likely influenced by autonomic tone. Some patients describe characteristic allergic symptoms, in the absence of typical IgE mediated triggers, and also improvement with traditional mast cell directed medications. Further work is necessary to determine whether these anecdotal observations are valid. The answer to this question will likely be addressed as the mechanisms of POTS are better characterized, which may include a phenotype with distinct mast cell involvement.

Induction of the Histamine-Forming Enzyme Histidine Decarboxylase in Skeletal Muscles by Prolonged Muscular Work: Histological Demonstration and Mediation by Cytokines

Recent studies suggest that histamine-a regulator of the microcirculation-may play important roles in exercise. We have shown that the histamine-forming enzyme histidine decarboxylase (HDC) is induced in skeletal muscles by prolonged muscular work (PMW). However, histological analysis of such HDC induction is lacking due to appropriate anti-HDC antibodies being unavailable. We also showed that the inflammatory cytokines interleukin (IL)-1 and tumor necrosis factor (TNF)-α can induce HDC, and that PMW increases both IL-1α and IL-1β in skeletal muscles. Here, we examined the effects (a) of PMW on the histological evidence of HDC induction and (b) of IL-1β and TNF-α on HDC activity in skeletal muscles. By immunostaining using a recently introduced commercial polyclonal anti-HDC antibody, we found that cells in the endomysium and around blood vessels, and also some muscle fibers themselves, became HDC-positive after PMW. After PMW, TNF-α, but not IL-1α or IL-1β, was detected in the blood serum. The minimum intravenous dose of IL-1β that would induce HDC activity was about 1/10 that of TNF-α, while in combination they synergistically augmented HDC activity. These results suggest that PMW induces HDC in skeletal muscles, including cells in the endomysium and around blood vessels, and also some muscle fibers themselves, and that IL-1β and TNF-α may cooperatively mediate this induction.

The Intriguing Role of Histamine in Exercise Responses

In humans, histamine is a molecular transducer of physical activity responses, and antihistamines modify more than 25% of the genes responding to exercise. Although the upstream signal that results in release of histamine within exercising skeletal muscle remains to be identified, it is likely a fundamental exercise response and not an allergic reaction.

The cardiovascular system after exercise

Recovery from exercise refers to the time period between the end of a bout of exercise and the subsequent return to a resting or recovered state. It also refers to specific physiological processes or states occurring after exercise that are distinct from the physiology of either the exercising or the resting states. In this context, recovery of the cardiovascular system after exercise occurs across a period of minutes to hours, during which many characteristics of the system, even how it is controlled, change over time. Some of these changes may be necessary for long-term adaptation to exercise training, yet some can lead to cardiovascular instability during recovery. Furthermore, some of these changes may provide insight into when the cardiovascular system has recovered from prior training and is physiologically ready for additional training stress. This review focuses on the most consistently observed hemodynamic adjustments and the underlying causes that drive cardiovascular recovery and will highlight how they differ following resistance and aerobic exercise. Primary emphasis will be placed on the hypotensive effect of aerobic and resistance exercise and associated mechanisms that have clinical relevance, but if left unchecked, can progress to symptomatic hypotension and syncope. Finally, we focus on the practical application of this information to strategies to maximize the benefits of cardiovascular recovery, or minimize the vulnerabilities of this state. We will explore appropriate field measures, and discuss to what extent these can guide an athlete's training.