Age and sex differences in microvascular responses during reactive hyperaemia.

Microvascular impairments are typical of several cardiovascular diseases. Near-infrared spectroscopy (NIRS) combined with a vascular occlusion test provides non-invasive insights into microvascular responses by monitoring skeletal muscle oxygenation changes during reactive hyperaemia. Despite increasing interest in the effects of sex and ageing on microvascular responses, evidence remains inconsistent. Therefore, the present study aimed to investigate the effects of sex and age on microvascular responsiveness. Twenty-seven participants (seven young men and seven young women; seven older men and six older women; aged 26 ± 1, 26 ± 4, 67 ± 3 and 69 ± 4 years, respectively) completed a vascular occlusion test consisting of 5 min of arterial occlusion followed by 5 min reperfusion. Oxygenation changes in the vastus lateralis were monitored by near-infrared spectroscopy. The findings revealed that both women (referring to young and older women) and older participants (referring to both men and women) exhibited lower microvascular responsiveness. Notably, both women and older participants demonstrated reduced desaturation (-38% and -59%, respectively) and reperfusion rates (-24% and -40%, respectively) along with a narrower range of tissue oxygenation (-39% and -39%, respectively) and higher minimal tissue oxygenation levels (+34% and +21%, respectively). Women additionally displayed higher values in resting (+12%) and time-to-peak (+15%) tissue oxygenation levels. In conclusion, this study confirmed decreased microvascular responses in women and older individuals. These results emphasize the importance of considering sex and age when studying microvascular responses. Further research is needed to uncover the underlying mechanisms and clinical relevance of these findings, enabling the development of tailored strategies for preserving vascular health in diverse populations.

Sex Differences in Test-Retest Reliability of Near-Infrared Spectroscopy During Postocclusive Reactive Hyperemia of the Vastus Lateralis.

ABSTRACT: Shoemaker, ME, Smith, CM, Gillen, ZM, and Cramer, JT. Sex differences in test-retest reliability of near-infrared spectroscopy during postocclusive reactive hyperemia of the vastus lateralis. J Strength Cond Res 38(2): e40-e48, 2024-The purpose of this study was to determine test-retest reliability for vascular reactivity measures and ranges for normalization of near-infrared spectroscopy (NIRS) variables from the vastus lateralis using postocclusive reactive hyperemia (PORH) procedure in male subjects, female subjects, and combined. Concentrations of oxygenated hemoglobin (Hb) + myoglobin (Mb) (O 2 Hb) and deoxygenated Hb + Mb (HHb) to derive total Hb + Mb (THb), difference in Hb + Mb signal (Hbdiff), and muscle tissue oxygen saturation (StO 2 ) from the vastus lateralis were measured during the PORH in 12 male subjects (age: 23.17 ± 1.77 years; stature: 180.88 ± 4.59 cm; and mass: 81.47 ± 9.68 kg) and 10 female subjects (age: 23.80 ± 2.07 years; stature: 165.95 ± 4.92 cm; and mass: 70.93 ± 10.55 kg) on 2 separate days. Adipose tissue thickness at the NIRS site was measured with ultrasonography. There were no significant differences between the mean values from visit 1 to visit 2 ( p > 0.076-0.985). In the composite sample, intraclass correlation coefficient (ICC) and coefficient of variation (CV) ranged from 0.35 to 0.91 and 4.74 to 39.18%, respectively. In male subjects, ICC and CV values ranged from 0.57 to 0.89 and 2.44 to 28.55%, respectively. In female subjects, ICC and CV values ranged from -0.05 to 0.75 and 7.83 to 61.19%, respectively. Although NIRS variables were overall reliable during PORH, when separated by sex, reliability in male subjects generally increased, whereas female subjects were not reliable, suggesting adipose tissue thickness may be a contributing factor. Understanding sex differences in reliability is important when using this technique for normalization or examining vascular reactivity during athletic performance. With greater utilization of NIRS monitoring in athletes to examine training adaptations, it is important for practitioners to understand the capabilities and potential limitations of the tool.

Glymphatic influx and clearance are accelerated by neurovascular coupling.

Functional hyperemia, also known as neurovascular coupling, is a phenomenon that occurs when neural activity increases local cerebral blood flow. Because all biological activity produces metabolic waste, we here sought to investigate the relationship between functional hyperemia and waste clearance via the glymphatic system. The analysis showed that whisker stimulation increased both glymphatic influx and clearance in the mouse somatosensory cortex with a 1.6-fold increase in periarterial cerebrospinal fluid (CSF) influx velocity in the activated hemisphere. Particle tracking velocimetry revealed a direct coupling between arterial dilation/constriction and periarterial CSF flow velocity. Optogenetic manipulation of vascular smooth muscle cells enhanced glymphatic influx in the absence of neural activation. We propose that impedance pumping allows arterial pulsatility to drive CSF in the same direction as blood flow, and we present a simulation that supports this idea. Thus, functional hyperemia boosts not only the supply of metabolites but also the removal of metabolic waste.

Reactive hyperemia half-time response is associated with skeletal muscle oxygen saturation changes during cycling exercise.

We investigated the relationship between muscle microvascular responses during reactive hyperemia as assessed using near-infrared spectroscopy (NIRS) with changes in skeletal muscle oxygen saturation during exercise. Thirty young untrained adults (M/W: 20/10; 23 ± 5 years) completed a maximal cycling exercise test to determine exercise intensities performed on a subsequent visit separated by seven days. At the second visit, post-occlusive reactive hyperemia was measured as changes in NIRS-derived tissue saturation index (TSI) at the left vastus lateralis muscle. Variables of interest included desaturation magnitude, resaturation rate, resaturation half-time, and hyperemic area under the curve. Afterwards, two 4-minute bouts of moderate intensity cycling followed by one bout of severe intensity cycling to fatigue took place while TSI was measured at the vastus lateralis muscle. TSI was averaged across the last 60-s of each moderate intensity bout then averaged together for analysis, and at 60-s into severe exercise. The change in TSI (∆TSI) during exercise is expressed relative to a 20 W cycling baseline. On average, the ΔTSI was -3.4 ± 2.4 % and -7.2 ± 2.8 % during moderate and severe intensity cycling, respectively. Resaturation half-time was correlated with the ΔTSI during moderate (r = -0.42, P = 0.01) and severe (r = -0.53, P = 0.002) intensity exercise. No other reactive hyperemia variable was found to correlate with ΔTSI. These results indicate that resaturation half-time during reactive hyperemia represents a resting muscle microvascular measure that associates with the degree of skeletal muscle desaturation during exercise in young adults.

Developmental toxicity of a pymetrozine photo-metabolite, 3-pyridinecarboxaldehyde, in zebrafish (Danio rerio) embryos: Abnormal cardiac development and occurrence of heart dysfunction via differential expression of heart formation-related genes.

Pymetrozine (PYM) is worldwide used to control sucking insect pests in rice-cultivated fields and it is degraded into various metabolites including 3-pyridinecarboxaldehyde (3-PCA). These two pyridine compounds were used to determine their impacts on aquatic environments, particularly on the aquatic animal model zebrafish (Danio rerio). PYM did not show acute toxicities in terms of lethality, hatching rate, and phenotypic changes in zebrafish embryos in the tested ranges up to a concentration of 20 mg/L. 3-PCA exhibited acute toxicity with LC50 and EC50 values of 10.7 and 2.07 mg/L, respectively. 3-PCA treatment caused phenotypic changes including pericardial edema, yolk sac edema, hyperemia, and curved spine, at a concentration of 10 mg/L after 48 h of exposure. Abnormal cardiac development was observed in 3-PCA-treated zebrafish embryos at a concentration of 5 mg/L with reduced heart function. In a molecular analysis, cacna1c, encoding a voltage-dependent calcium channel, was significantly down-regulated in the 3-PCA-treated embryos, indicating synaptic and behavioral defects. Hyperemia and incomplete intersegmental vessels were observed in 3-PCA-treated embryos. Based on these results, it is necessary to generate scientific information on the acute and chronic toxicity of PYM and its metabolites with regular monitoring of their residues in aquatic environments.

Mechanisms that underlie blood flow regulation at rest and during exercise.

The cardiovascular system must distribute oxygen and nutrients to the body while maintaining appropriate blood pressure. This is achieved through a combination of central and peripheral mechanisms that influence cardiac output and vasomotor tone throughout the vascular system. Furthermore, the capability to preferentially direct blood to tissues with increased metabolic demand (i.e., active hyperemia) is crucial to exercise tolerance. However, the interaction between these systems is difficult to understand without real-life examples. Fortunately, monitoring blood flow, blood pressure, and heart rate during a series of laboratory protocols will allow students to partition the contributions of these central and peripheral factors. The three protocols include 1) reactive hyperemia in the forearm, 2) small muscle mass handgrip exercise, and 3) large muscle mass cycling exercise. In addition to providing a detailed description of the required equipment, specific protocols, and expected outcomes, this report also reviews some of the common student misconceptions that are associated with the observed physiological responses.NEW & NOTEWORTHY Blood flow regulation during exercise is a complicated process that involves many overlapping mechanisms. This laboratory will help students better understand how the body regulates blood flow to the active muscles using three separate protocols: 1) reactive hyperemia, 2) small muscle mass exercise, and 3) large muscle mass exercise.

PECULIARITIES OF VASOR-REGULATING FUNCTIONS OF THE VASCULAR ENDOTHELIUM IN ADAPTATION OF THE YOUTH BODY TO SYSTEMATIC PHYSICAL LOADS.

OBJECTIVE: The aim: To analyze the features of changes in the functional state of the vascular endothelium of handball players in the dynamics of the training process, at different levels of the body's hypoxic state. PATIENTS AND METHODS: Materials and methods: Theoretical methods, the method of Corretti et al. with the use of high-resolution ultrasound, Fisher test with the calculation of the Fisher criterion and the Bland-Altman method. The study of the vasomotor function of the vascular endothelium was carried out of young men 18-20 y.o., who did not go in for sports and which were systematically played handball. The brachial artery diameter, maximum linear blood flow velocity, volumetric blood flow velocity were registered in the state of relative rest after artificially created reactive hyperemia. RESULTS: Results: The primary results obtained showed that in the process of long-term adaptation to systematic muscular work, a pronounced vasodilation effect was observed. Subsequent analyze of changes in the functional state of the vascular endothelium of young sportsmen during the macrocycle preparation different levels of the body's hypoxic state manifested the following. The young men-athletes had more pronounced vasodilation effect, the values of the linear and volumetric blood flow velocity both in the state of relative rest and at the peak of the artificially created hyperemia were significantly higher than in the young men, who did not go in for sports. CONCLUSION: Conclusions: Suggested that the systematic muscular work contributes to a significant intensification of the oxidation pathway of nitric oxide formation from L-arginine with the participation of endothelial NO-synthase.

Neurovascular coupling: motive unknown.

In the brain, increases in neural activity drive changes in local blood flow via neurovascular coupling. The common explanation for increased blood flow (known as functional hyperemia) is that it supplies the metabolic needs of active neurons. However, there is a large body of evidence that is inconsistent with this idea. Baseline blood flow is adequate to supply oxygen needs even with elevated neural activity. Neurovascular coupling is irregular, absent, or inverted in many brain regions, behavioral states, and conditions. Increases in respiration can increase brain oxygenation without flow changes. Simulations show that given the architecture of the brain vasculature, areas of low blood flow are inescapable and cannot be removed by functional hyperemia. As discussed in this article, potential alternative functions of neurovascular coupling include supplying oxygen for neuromodulator synthesis, brain temperature regulation, signaling to neurons, stabilizing and optimizing the cerebral vascular structure, accommodating the non-Newtonian nature of blood, and driving the production and circulation of cerebrospinal fluid (CSF).

Global REACH 2018: increased adrenergic restraint of blood flow preserves coupling of oxygen delivery and demand during exercise at high-altitude.

Chronic exposure to hypoxia (high-altitude, HA; >4000 m) attenuates the vasodilatory response to exercise and is associated with a persistent increase in basal sympathetic nerve activity (SNA). The mechanism(s) responsible for the reduced vasodilatation and exercise hyperaemia at HA remains unknown. We hypothesized that heightened adrenergic signalling restrains skeletal muscle blood flow during handgrip exercise in lowlanders acclimatizing to HA. We tested nine adult males (n = 9) at sea-level (SL; 344 m) and following 21-28 days at HA (∼4300 m). Forearm blood flow (FBF; duplex ultrasonography), mean arterial pressure (MAP; brachial artery catheter), forearm vascular conductance (FVC; FBF/MAP), and arterial and venous blood sampling (O2 delivery ( DO2${D}_{{{\rm{O}}}_{\rm{2}}}$ ) and uptake ( V̇O2${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ )) were measured at rest and during graded rhythmic handgrip exercise (5%, 15% and 25% of maximum voluntary isometric contraction; MVC) before and after local α- and ß-adrenergic blockade (intra-arterial phentolamine and propranolol). HA reduced ΔFBF (25% MVC: SL: 138.3 ± 47.6 vs. HA: 113.4 ± 37.1 ml min-1 ; P = 0.022) and Δ V̇O2${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ (25% MVC: SL: 20.3 ± 7.5 vs. HA: 14.3 ± 6.2 ml min-1 ; P = 0.014) during exercise. Local adrenoreceptor blockade at HA restored FBF during exercise (25% MVC: SLα-ß blockade : 164.1 ± 71.7 vs. HAα-ß blockade : 185.4 ± 66.6 ml min-1 ; P = 0.947) but resulted in an exaggerated relationship between DO2${D}_{{{\rm{O}}}_{\rm{2}}}$ and V̇O2${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ ( DO2${D}_{{{\rm{O}}}_{\rm{2}}}$ / V̇O2${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ slope: SL: 1.32; HA: slope: 1.86; P = 0.037). These results indicate that tonic adrenergic signalling restrains exercise hyperaemia in lowlanders acclimatizing to HA. The increase in adrenergic restraint is necessary to match oxygen delivery to demand and prevent over perfusion of contracting muscle at HA. KEY POINTS: In exercising skeletal muscle, local vasodilatory signalling and sympathetic vasoconstriction integrate to match oxygen delivery to demand and maintain arterial blood pressure. Exposure to chronic hypoxia (altitude, >4000 m) causes a persistent increase in sympathetic nervous system activity that is associated with impaired functional capacity and diminished vasodilatation during exercise. In healthy male lowlanders exposed to chronic hypoxia (21-28 days; ∼4300 m), local adrenoreceptor blockade (combined α- and ß-adrenergic blockade) restored skeletal muscle blood flow during handgrip exercise. However, removal of tonic adrenergic restraint at high altitude caused an excessive rise in blood flow and subsequently oxygen delivery for any given metabolic demand. This investigation is the first to identify greater adrenergic restraint of blood flow during acclimatization to high altitude and provides evidence of a functional role for this adaptive response in regulating oxygen delivery and demand.

Crosstalk between adenosine receptors and CYP450-derived oxylipins in the modulation of cardiovascular, including coronary reactive hyperemic response.

Adenosine is a ubiquitous endogenous nucleoside or autacoid that affects the cardiovascular system through the activation of four G-protein coupled receptors: adenosine A1 receptor (A1AR), adenosine A2A receptor (A2AAR), adenosine A2B receptor (A2BAR), and adenosine A3 receptor (A3AR). With the rapid generation of this nucleoside from cellular metabolism and the widespread distribution of its four G-protein coupled receptors in almost all organs and tissues of the body, this autacoid induces multiple physiological as well as pathological effects, not only regulating the cardiovascular system but also the central nervous system, peripheral vascular system, and immune system. Mounting evidence shows the role of CYP450-enzymes in cardiovascular physiology and pathology, and the genetic polymorphisms in CYP450s can increase susceptibility to cardiovascular diseases (CVDs). One of the most important physiological roles of CYP450-epoxygenases (CYP450-2C & CYP2J2) is the metabolism of arachidonic acid (AA) and linoleic acid (LA) into epoxyeicosatrienoic acids (EETs) and epoxyoctadecaenoic acid (EpOMEs) which generally involve in vasodilation. Like an increase in coronary reactive hyperemia (CRH), an increase in anti-inflammation, and cardioprotective effects. Moreover, the genetic polymorphisms in CYP450-epoxygenases will change the beneficial cardiovascular effects of metabolites or oxylipins into detrimental effects. The soluble epoxide hydrolase (sEH) is another crucial enzyme ubiquitously expressed in all living organisms and almost all organs and tissues. However, in contrast to CYP450-epoxygenases, sEH converts EETs into dihydroxyeicosatrienoic acid (DHETs), EpOMEs into dihydroxyoctadecaenoic acid (DiHOMEs), and others and reverses the beneficial effects of epoxy-fatty acids leading to vasoconstriction, reducing CRH, increase in pro-inflammation, increase in pro-thrombotic and become less cardioprotective. Therefore, polymorphisms in the sEH gene (Ephx2) cause the enzyme to become overactive, making it more vulnerable to CVDs, including hypertension. Besides the sEH, ω-hydroxylases (CYP450-4A11 & CYP450-4F2) derived metabolites from AA, ω terminal-hydroxyeicosatetraenoic acids (19-, 20-HETE), lipoxygenase-derived mid-chain hydroxyeicosatetraenoic acids (5-, 11-, 12-, 15-HETEs), and the cyclooxygenase-derived prostanoids (prostaglandins: PGD2, PGF2α; thromboxane: Txs, oxylipins) are involved in vasoconstriction, hypertension, reduction in CRH, pro-inflammation and cardiac toxicity. Interestingly, the interactions of adenosine receptors (A2AAR, A1AR) with CYP450-epoxygenases, ω-hydroxylases, sEH, and their derived metabolites or oxygenated polyunsaturated fatty acids (PUFAs or oxylipins) is shown in the regulation of the cardiovascular functions. In addition, much evidence demonstrates polymorphisms in CYP450-epoxygenases, ω-hydroxylases, and sEH genes (Ephx2) and adenosine receptor genes (ADORA1 & ADORA2) in the human population with the susceptibility to CVDs, including hypertension. CVDs are the number one cause of death globally, coronary artery disease (CAD) was the leading cause of death in the US in 2019, and hypertension is one of the most potent causes of CVDs. This review summarizes the articles related to the crosstalk between adenosine receptors and CYP450-derived oxylipins in vascular, including the CRH response in regular salt-diet fed and high salt-diet fed mice with the correlation of heart perfusate/plasma oxylipins. By using A2AAR-/-, A1AR-/-, eNOS-/-, sEH-/- or Ephx2-/-, vascular sEH-overexpressed (Tie2-sEH Tr), vascular CYP2J2-overexpressed (Tie2-CYP2J2 Tr), and wild-type (WT) mice. This review article also summarizes the role of pro-and anti-inflammatory oxylipins in cardiovascular function/dysfunction in mice and humans. Therefore, more studies are needed better to understand the crosstalk between the adenosine receptors and eicosanoids to develop diagnostic and therapeutic tools by using plasma oxylipins profiles in CVDs, including hypertensive cases in the future.

Topical Porphyrin Antioxidant Protects Against Ocular Surface Pathology in a Novel Rabbit Model for Particulate Matter-Induced Dry Eye Disease.

Purpose: Particulate matter (PM) is a primary cause for the development of acute and chronic dry eye disease, especially irritant-induced conjunctivitis. The purpose of the present study was to determine the effects of fine atmospheric PM on the rabbit ocular surface, and determine the protective effects of a synthetic antioxidant, manganese(III) tetrakis(1-methyl-4-pyridyl) porphyrin (Mn-TM-2-PyP), in vitro and in vivo. Methods: Rabbit corneal epithelial cells (SIRC) were exposed to increasing concentrations of PM to determine the effects on cell motility and viability. The in vivo effects of topically instilled PM were tested in New Zealand White rabbits. Comprehensive ophthalmic exams and corneal fluorescein staining were performed. Results: Exposure to PM resulted in dose-dependent cell death and impaired cellular motility; Mn-TM-2-PyP protected against PM-induced cytotoxicity and significantly increased SIRC cell motility. In vivo, exposure to PM (5 mg/ml, topical, 3 times daily for 7 days) resulted in signs of dry eye, notably hyperemia, increased corneal fluorescein staining, and decreased tear volumes. Mn-TM-2-PyP significantly improved hyperemia and corneal fluorescein readouts but had no effect on tear production. Lifitegrast (Xiidra®) showed similar pharmacologic efficacy to Mn-TM-2-PyP. Conclusion: Overall, these data provide evidence that PM induces phenotypes of ocular surface disease responsive to antioxidant and immunosuppressant therapy. To our knowledge this is the first report of a large animal model to study PM-induced ocular surface disease. The present work provides standardized experimental paradigms for the comprehensive in vitro and in vivo testing of novel therapeutic approaches targeting PM-induced conjunctivitis and dry-eye.

The cholinergic system modulates negative BOLD responses in the prefrontal cortex once electrical perforant pathway stimulation triggers neuronal afterdischarges in the hippocampus.

Repeated high-frequency pulse-burst stimulations of the rat perforant pathway elicited positive BOLD responses in the right hippocampus, septum and prefrontal cortex. However, when the first stimulation period also triggered neuronal afterdischarges in the hippocampus, then a delayed negative BOLD response in the prefrontal cortex was generated. While neuronal activity and cerebral blood volume (CBV) increased in the hippocampus during the period of hippocampal neuronal afterdischarges (h-nAD), CBV decreased in the prefrontal cortex, although neuronal activity did not decrease. Only after termination of h-nAD did CBV in the prefrontal cortex increase again. Thus, h-nAD triggered neuronal activity in the prefrontal cortex that counteracted the usual neuronal activity-related functional hyperemia. This process was significantly enhanced by pilocarpine, a mACh receptor agonist, and completely blocked when pilocarpine was co-administered with scopolamine, a mACh receptor antagonist. Scopolamine did not prevent the formation of the negative BOLD response, thus mACh receptors modulate the strength of the negative BOLD response.

Influence of dietary intervention on microvascular endothelial function in coronary patients and atherothrombotic risk of recurrence.

Endothelial dysfunction is a key player in both the onset and development of atherosclerosis. No study has examined whether healthy dietary patterns can improve microvascular endothelial function in patients with coronary heart disease (CHD) in the long-term and whether this relationship can affect patient's risk of CHD recurrence. In the CORDIOPREV study, a randomized, double-blind, controlled trial, dietary intervention with either the Mediterranean diet or a low-fat diet was implemented in 1,002 CHD patients. A laser-doppler flowmetry was performed at baseline and after 6 years of follow up in 664 patients, evaluating the effects of this dietary intervention on microvascular basal flow and reactive hyperaemia area, as well as on the risk of CHD recurrence, based on the TRS2P risk score. Basal flow (97.78 ± 2.79 vs. 179.31 ± 5.06 arbitrary perfusion units, 83.38% increase, p < 0.001) and reactive hyperaemia area (4233.3 ± 127.73 vs. 9695.9 ± 205.23 arbitrary perfusion units per time, 129.04% increase, p < 0.001) improved after the dietary intervention in the cohort, without finding differences due to the diet (p > 0.05 for the diet-effect). When patients were stratified to low, moderate or high-risk of recurrence, basal flow was similarly increased in all three groups. However, reactive hyperaemia area was improved to a greater extent in patients at the low-risk group compared with those at moderate or high-risk. No differences were observed between diets. Healthy dietary patterns can improve microvascular endothelial function and this improvement persists in the long-term. Patients with a low-risk of CHD recurrence show a greater improvement in reactive vasodilation to ischemia than patients in the moderate or high-risk groups.

MicroRNAs targeting VEGF are related to vascular dysfunction in preeclampsia.

In preeclampsia (PE), pre-existent maternal endothelial dysfunction leads to impaired placentation and vascular maladaptation. The vascular endothelial growth factor (VEGF) pathway is essential in the placentation process and VEGF expression is regulated through post-transcriptional modification by microRNAs (miRNAs). We investigated the expression of VEGF-related circulating miR-16, miR-29b, miR-126, miR-155 and miR-200c in PE vs healthy pregnancies (HPs), and their relation with vascular function, oxidative stress (OS) and systemic inflammation. In this case-control study, 24 women with early PE (<34 weeks) were compared with 30 women with HP. Circulating microRNA levels (RT-qPCR), OS and systemic inflammation were assessed in plasma samples (PE 29.5 vs HP 25.8 weeks) and related to extensive in vivo vascular function (flow-mediated dilatation (FMD), modified FMD (mFMD), carotid-femoral pulse wave velocity (CF-PWV), heart rate corrected augmentation index (AIx75) and reactive hyperemia index (RHI)). FMD, CF-PWV, AIx75 and RHI were all significantly impaired in PE (P<0.05). PE patients had reduced levels of miR-16 (5.53 ± 0.36 vs 5.84 ± 0.61) and increased levels of miR-200c (1.34 ± 0.57 vs 0.97 ± 0.68) (P<0.05). Independent of age and parity, miR-16 was related to impaired FMD (ß 2.771, 95% C.I.: 0.023-5.519, P=0.048) and mFMD (ß 3.401, 95% C.I.: 0.201-6.602, P=0.038). Likewise, miR-200c was independently associated with CF-PWV (ß 0.513, 95% C.I.: 0.034-0.992, P=0.036). In conclusion, circulating levels of miR-16 were lower in PE, which correlated with impaired endothelial function. Circulating miR-200c was increased in PE and correlated with higher arterial stiffness. These findings suggest a post-transcriptional dysregulation of the VEGF pathway in PE and identify miR-16 and miR-200c as possible diagnostic biomarkers for PE.

Detection of blood flow perfusion and post - occlusive reactive hyperemia in the skeletal muscle of rats.

AIMS: Post-occlusive reactive hyperemia (PORH) remains poorly understood in the skeletal muscle system. This study was designed to validate an alternative strategy of PORH detection in rodents. Additionally, we explored the hypothesis that PORH is influenced by experimental models associated with impaired function of the skeletal muscle. MATERIALS AND METHODS: Wistar rats were anesthetized, and blood flow was assessed by laser Doppler in the anterior tibialis muscle, before and immediately after 5 s, 30 s, 3 min, or 5 min of flow occlusion, obtained through a cuff inflated to 300 mmHg around the thigh of the animals. KEY FINDINGS: In healthy animals, deflating the cuff resulted in a fast increment of local blood flow, characterizing the PORH after 5 s to 5 min of cuff occlusion and its dependence on flow occlusion duration. Importantly, we found different profiles of PORH in animals pretreated with reserpine (accelerated peak and reduced half recovery time), streptozotocin (increased peak), or subjected to muscle contraction in stretching (delayed peak), approaches used as experimental models to study fibromyalgia, type II diabetes mellitus, and soreness induced by unaccustomed eccentric exercise, respectively. SIGNIFICANCE: We demonstrated that the profile of PORH in the anterior tibialis muscle of rats is sensitive to a variety of experimental models often associated with the skeletal muscle functionality, providing a useful strategy to explore how and whether changes in local regulation of blood flow can contribute to the development of skeletal muscle associated symptoms in clinically relevant conditions.

PIP2 corrects cerebral blood flow deficits in small vessel disease by rescuing capillary Kir2.1 activity.

Cerebral small vessel diseases (SVDs) are a central link between stroke and dementia-two comorbidities without specific treatments. Despite the emerging consensus that SVDs are initiated in the endothelium, the early mechanisms remain largely unknown. Deficits in on-demand delivery of blood to active brain regions (functional hyperemia) are early manifestations of the underlying pathogenesis. The capillary endothelial cell strong inward-rectifier K+ channel Kir2.1, which senses neuronal activity and initiates a propagating electrical signal that dilates upstream arterioles, is a cornerstone of functional hyperemia. Here, using a genetic SVD mouse model, we show that impaired functional hyperemia is caused by diminished Kir2.1 channel activity. We link Kir2.1 deactivation to depletion of phosphatidylinositol 4,5-bisphosphate (PIP2), a membrane phospholipid essential for Kir2.1 activity. Systemic injection of soluble PIP2 rapidly restored functional hyperemia in SVD mice, suggesting a possible strategy for rescuing functional hyperemia in brain disorders in which blood flow is disturbed.

PIP2 Improves Cerebral Blood Flow in a Mouse Model of Alzheimer's Disease.

Alzheimer's disease (AD) is a leading cause of dementia and a substantial healthcare burden. Despite this, few treatment options are available for controlling AD symptoms. Notably, neuronal activity-dependent increases in cortical cerebral blood flow (CBF; functional hyperemia) are attenuated in AD patients, but the associated pathological mechanisms are not fully understood at the molecular level. A fundamental mechanism underlying functional hyperemia is activation of capillary endothelial inward-rectifying K+ (Kir2.1) channels by neuronally derived potassium (K+), which evokes a retrograde capillary-to-arteriole electrical signal that dilates upstream arterioles, increasing blood delivery to downstream active regions. Here, using a mouse model of familial AD (5xFAD), we tested whether this impairment in functional hyperemia is attributable to reduced activity of capillary Kir2.1 channels. In vivo CBF measurements revealed significant reductions in whisker stimulation (WS)-induced and K+-induced hyperemic responses in 5xFAD mice compared with age-matched controls. Notably, measurements of whole-cell currents in freshly isolated 5xFAD capillary endothelial cells showed that Kir2.1 current density was profoundly reduced, suggesting a defect in Kir2.1 function. Because Kir2.1 activity absolutely depends on binding of phosphatidylinositol 4,5-bisphosphate (PIP2) to the channel, we hypothesized that capillary Kir2.1 channel impairment could be corrected by exogenously supplying PIP2. As predicted, a PIP2 analog restored Kir2.1 current density to control levels. More importantly, systemic administration of PIP2 restored K+-induced CBF increases and WS-induced functional hyperemic responses in 5xFAD mice. Collectively, these data provide evidence that PIP2-mediated restoration of capillary endothelial Kir2.1 function improves neurovascular coupling and CBF in the setting of AD.

TRPV4 channel blockade does not modulate skin vasodilation and sweating during hyperthermia or cutaneous postocclusive reactive and thermal hyperemia.

Transient receptor potential vanilloid 4 (TRPV4) channels exist on vascular endothelial cells and eccrine sweat gland secretory cells in human skin. Here, we assessed whether TRPV4 channels contribute to cutaneous vasodilation and sweating during whole body passive heat stress (protocol 1) and to cutaneous vasodilation during postocclusive reactive hyperemia and local thermal hyperemia (protocol 2). Intradermal microdialysis was employed to locally deliver pharmacological agents to forearm skin sites, where cutaneous vascular conductance (CVC) and sweat rate were assessed. In protocol 1 (12 young adults), CVC and sweat rate were increased by passive whole body heating, resulting in a body core temperature elevation of 1.2 ± 0.1°C. The elevated CVC and sweat rate assessed at sites treated with TRPV4 channel antagonist (either 200 µM HC-067047 or 125 µM GSK2193874) were not different from the vehicle control site (5% dimethyl sulfoxide). After whole body heating, the TRPV4 channel agonist (100 µM GSK1016790A) was administered to each skin site, eliciting elevations in CVC. Relative to control, this response was partly attenuated by both TRPV4 channel antagonists, confirming drug efficacy. In protocol 2 (10 young adults), CVC was increased following a 5-min arterial occlusion and during local heating from 33 to 42°C. These responses did not differ between the control and the TRPV4 channel antagonist sites (200 µM HC-067047). We show that TRPV4 channels are not required for regulating cutaneous vasodilation or sweating during a whole body passive heat stress. Furthermore, they are not required for regulating cutaneous vasodilation during postocclusive reactive hyperemia and local thermal hyperemia.

Greater α1-adrenergic-mediated vasoconstriction in contracting skeletal muscle of patients with type 2 diabetes.

Patients with type 2 diabetes mellitus (T2DM) exhibit diminished exercise capacity likely attributable to reduced skeletal muscle blood flow (i.e., exercise hyperemia). A potential underlying mechanism of the impaired hyperemic response to exercise could be inadequate blunting of sympathetic-mediated vasoconstriction (i.e., poor functional sympatholysis). Therefore, we studied the hyperemic and vasodilatory responses to handgrip exercise in patients with T2DM as well as vasoconstriction to selective α-agonist infusion. Forearm blood flow (FBF) and vascular conductance (FVC) were examined in patients with T2DM (n = 30) as well as nondiabetic controls (n = 15) with similar age (59 ± 9 vs. 60 ± 9 yr, P = 0.69) and body mass index (31.4 ± 5.2 vs. 29.5 ± 4.6 kg/m2, P = 0.48). Intra-arterial infusion of phenylephrine (α1-agonist) and dexmedetomidine (α2-agonist) were used to induce vasoconstriction: [(FVCwith drug - FVCpredrug)/FVCpredrug × 100%]. Subjects completed rest and dynamic handgrip exercise (20% of maximum) trials per α-agonist. Patients with T2DM had smaller increases (Δ from rest) in FBF (147 ± 71 vs. 199 ± 63 ml/min) and FVC (126 ± 58 vs. 176 ± 50 ml·min-1·100 mmHg-1, P < 0.01 for both) during exercise compared with controls, respectively. During exercise, patients with T2DM had greater α1- (-16.9 ± 5.9 vs. -11.3 ± 3.8%) and α2-mediated vasoconstriction (-23.5 ± 7.1 vs. -19.0 ± 6.5%, P < 0.05 for both) versus controls. The magnitude of sympatholysis (Δ in %vasoconstriction between exercise and rest) for PE was lower (worse) in patients with T2DM versus controls (14.9 ± 12.2 vs. 23.1 ± 8.1%, P < 0.05) whereas groups were similar during DEX trials (24.6 ± 12.3 vs. 27.6 ± 13.4%, P = 0.47). Our data suggest patients with T2DM have attenuated hyperemic and vasodilatory responses to exercise, which could be attributable to greater α1-mediated vasoconstriction in contracting skeletal muscle.NEW & NOTEWORTHY Findings presented in this article are the first to show patients with type 2 diabetes mellitus have blunted hyperemic and vasodilatory responses to dynamic handgrip exercise. Moreover, we illustrate greater α1-adrenergic-mediated vasoconstriction may contribute to our initial observations. Collectively, these data suggest patients with type 2 diabetes may have impaired functional sympatholysis, which can contribute to their reduced exercise capacity.

Functional hyperemia drives fluid exchange in the paravascular space.

The brain lacks a conventional lymphatic system to remove metabolic waste. It has been proposed that directional fluid movement through the arteriolar paravascular space (PVS) promotes metabolite clearance. We performed simulations to examine if arteriolar pulsations and dilations can drive directional CSF flow in the PVS and found that arteriolar wall movements do not drive directional CSF flow. We propose an alternative method of metabolite clearance from the PVS, namely fluid exchange between the PVS and the subarachnoid space (SAS). In simulations with compliant brain tissue, arteriolar pulsations did not drive appreciable fluid exchange between the PVS and the SAS. However, when the arteriole dilated, as seen during functional hyperemia, there was a marked exchange of fluid. Simulations suggest that functional hyperemia may serve to increase metabolite clearance from the PVS. We measured blood vessels and brain tissue displacement simultaneously in awake, head-fixed mice using two-photon microscopy. These measurements showed that brain deforms in response to pressure changes in PVS, consistent with our simulations. Our results show that the deformability of the brain tissue needs to be accounted for when studying fluid flow and metabolite transport.