Capillary regression leads to sustained local hypoperfusion by inducing constriction of upstream transitional vessels.

In the brain, a microvascular sensory web coordinates oxygen delivery to regions of neuronal activity. This involves a dense network of capillaries that send conductive signals upstream to feeding arterioles to promote vasodilation and blood flow. Although this process is critical to the metabolic supply of healthy brain tissue, it may also be a point of vulnerability in disease. Deterioration of capillary networks is a feature of many neurological disorders and injuries and how this web is engaged during vascular damage remains unknown. We performed in vivo two-photon microscopy on young adult mural cell reporter mice and induced focal capillary injuries using precise two-photon laser irradiation of single capillaries. We found that ~59% of the injuries resulted in regression of the capillary segment 7 to 14 d following injury, and the remaining repaired to reestablish blood flow within 7 d. Injuries that resulted in capillary regression induced sustained vasoconstriction in the upstream arteriole-capillary transition (ACT) zone at least 21 days postinjury in both awake and anesthetized mice. The degree of vasomotor dynamics was chronically attenuated in the ACT zone consequently reducing blood flow in the ACT zone and in secondary, uninjured downstream capillaries. These findings demonstrate how focal capillary injury and regression can impair the microvascular sensory web and contribute to cerebral hypoperfusion.

Deciphering the kidney hemodynamic effects of SGLT2 inhibition: translating insights from rats to humans in type 2 diabetes.

The attenuation of glomerular hyperfiltration is posited to be a principal mechanism underlying the kidney protective effects of sodium-glucose cotransporter-2 (SGLT2) inhibitors in diabetic kidney disease. Notably, the impact of SGLT2 inhibitors on kidney hemodynamic function has been posited to vary between type 1 and type 2 diabetes. The study by Wada et al. documents that in an animal model of type 2 diabetes, SGLT2 inhibitors mitigate glomerular hyperfiltration predominantly through afferent arteriolar constriction, a process mediated by the adenosine/A1 receptor pathway. This observation is consistent with mechanisms identified in type 1 diabetes, arguing for similar methods in type 1 and 2 diabetes.

Thrombin in Pregnancy and Preeclampsia: Expression, Localization, and Vasoactivity in Brain and Microvessels From Rats.

ABSTRACT: Thrombin is a coagulation factor increased in pregnancy and further increased in preeclampsia (PE), a hypertensive disorder. Thrombin is also expressed in the brain and may have a nonhemostatic role. We characterized thrombin expression and vasoactivity in brain cerebral parenchymal arterioles (PAs) in rat models of pregnancy and PE. PAs were isolated and pressurized from nonpregnant (NP) and late-pregnant (LP) rats and rats with experimental preeclampsia (ePE). Reactivity to thrombin (1-50 U/mL) was measured in the absence and presence of inhibition of cyclooxygenase and nitric oxide synthase. Plasma levels of prothrombin, thrombin-antithrombin (TAT), tissue plasminogen activator, and plasminogen activator inhibitor-1 (PAI-1) and cerebrospinal fluid levels of TAT were compared using enzyme-linked immunosorbent assay. Expression of protease-activated receptor types 1 and 2 in PAs were measured by Western blot and immunohistochemistry. Neuronal thrombin expression was quantified in brains from all groups by immunohistochemistry. Prothrombin and TAT were elevated in ePE plasma compared with NP and LP. TAT was detected in cerebrospinal fluid from all groups and significantly elevated in LP (NP: 0.137 ± 0.014 ng/mL, LP: 0.241 ± 0.015 ng/mL, ePE: 0.192 ± 0.028 ng/mL; P < 0.05). Thrombin caused modest vasoconstriction in PAs from all groups regardless of cyclooxygenase or nitric oxide synthase inhibition. PAR1 and PAR2 were found in PAs from all groups colocalized to smooth muscle. Thrombin expression in central neurons was decreased in both LP and ePE groups compared with NP. These findings suggest a role for thrombin and other hemostatic changes during pregnancy and PE beyond coagulation.

Evaluation of glomerular hemodynamic changes by sodium-glucose-transporter 2 inhibition in type 2 diabetic rats using in vivo imaging.

The mechanisms responsible for glomerular hemodynamic regulation with sodium-glucose co-transporter 2 (SGLT2) inhibitors in kidney disease due to type 2 diabetes remain unclear. Therefore, we investigated changes in glomerular hemodynamic function using an animal model of type 2 diabetes, treated with an SGLT2 inhibitor alone or in combination with a renin-angiotensin-aldosterone system inhibitor using male Zucker lean (ZL) and Zucker diabetic fatty (ZDF) rats. Afferent and efferent arteriolar diameter and single-nephron glomerular filtration rate (SNGFR) were evaluated in ZDF rats measured at 0, 30, 60, 90, and 120 minutes after the administration of a SGLT2 inhibitor (luseogliflozin). Additionally, we assessed these changes under the administration of the adenosine A1 receptor (A1aR) antagonist (8-cyclopentyl-1,3-dipropylxanthine), along with coadministration of luseogliflozin and an angiotensin II receptor blocker (ARB), telmisartan. ZDF rats had significantly increased SNGFR, and afferent and efferent arteriolar diameters compared to ZL rats, indicating glomerular hyperfiltration. Administration of luseogliflozin significantly reduced afferent vasodilatation and glomerular hyperfiltration, with no impact on efferent arteriolar diameter. Urinary adenosine levels were increased significantly in the SGLT2 inhibitor group compared to the vehicle group. A1aR antagonism blocked the effect of luseogliflozin on kidney function. Co-administration of the SGLT2 inhibitor and ARB decreased the abnormal expansion of glomerular afferent arterioles, whereas the efferent arteriolar diameter was not affected. Thus, regulation of afferent arteriolar vascular tone via the A1aR pathway is associated with glomerular hyperfiltration in type 2 diabetic kidney disease.

Patients with uncontrolled hypertension subjected to cardiopulmonary bypass have altered coronary vasomotor responses to serotonin.

BACKGROUND: We previously found that cardioplegic arrest and cardiopulmonary bypass are associated with altered coronary arteriolar response to serotonin in patients undergoing cardiac surgery. In this study, we investigated the effects of hypertension on coronary microvascular vasomotor tone in response to serotonin and alterations in serotonin receptor protein expression in the setting of cardioplegic arrest and cardiopulmonary bypass. METHODS: Coronary arterioles were dissected from harvested pre- and post-cardioplegic arrest and cardiopulmonary bypass right atrial tissue samples of patients undergoing cardiac surgery with normotension, well-controlled hypertension, and uncontrolled hypertension. Vasomotor tone was assessed by video-myography, and protein expression was measured with immunoblotting. RESULTS: Pre-cardioplegic arrest and cardiopulmonary bypass, serotonin induced moderate relaxation responses of coronary arterioles in normotension and well-controlled hypertension patients, whereas serotonin caused moderate contractile responses in uncontrolled hypertension patients. Post-cardioplegic arrest and cardiopulmonary bypass, serotonin caused contractile responses of coronary arterioles in all 3 groups. The post-cardioplegic arrest and cardiopulmonary bypass contractile response to serotonin was significantly higher in the uncontrolled hypertension group compared with the normotension or well-controlled hypertension groups (P < .05). Pre-cardioplegic arrest and cardiopulmonary bypass, expression of the serotonin 1A receptor was significantly lower in the uncontrolled hypertension group compared with the well-controlled hypertension and normotension groups (P = .01 and P < .001). Serotonin 1B receptor expression was higher in the uncontrolled hypertension group compared with the normotension or well-controlled hypertension groups post-cardioplegic arrest and cardiopulmonary bypass (P = .03 and P = .046). CONCLUSION: Uncontrolled hypertension is associated with an increased coronary contractile response of coronary microvessels to serotonin and altered serotonin receptor protein expression after cardioplegic arrest and cardiopulmonary bypass. These findings may contribute to a worse postoperative coronary spasm and worsened recovery of coronary perfusion in patients with uncontrolled hypertension after cardioplegic arrest and cardiopulmonary bypass and cardiac surgery.

Pulmonary hypertension impairs vasomotor function in rat diaphragm arterioles.

Pulmonary hypertension (PH) is a chronic, progressive condition in which respiratory muscle dysfunction is a primary contributor to exercise intolerance and dyspnea in patients. Contractile function, blood flow distribution, and the hyperemic response are altered in the diaphragm with PH, and we sought to determine whether this may be attributed, in part, to impaired vasoreactivity of the resistance vasculature. We hypothesized that there would be blunted endothelium-dependent vasodilation and impaired myogenic responsiveness in arterioles from the diaphragm of PH rats. Female Sprague-Dawley rats were randomized into healthy control (HC, n = 9) and monocrotaline-induced PH rats (MCT, n = 9). Endothelium-dependent and -independent vasodilation and myogenic responses were assessed in first-order arterioles (1As) from the medial costal diaphragm in vitro. There was a significant reduction in endothelium-dependent (via acetylcholine; HC, 78 ± 15% vs. MCT, 47 ± 17%; P < 0.05) and -independent (via sodium nitroprusside; HC, 89 ± 10% vs. MCT, 66 ± 10%; P < 0.05) vasodilation in 1As from MCT rats. MCT-induced PH also diminished myogenic constriction (P < 0.05) but did not alter passive pressure responses. The diaphragmatic weakness, impaired hyperemia, and blood flow redistribution associated with PH may be due, in part, to diaphragm vascular dysfunction and thus compromised oxygen delivery which occurs through both endothelium-dependent and -independent mechanisms.

Mid- to Late-Life Time-Averaged Cumulative Blood Pressure and Late-Life Retinal Microvasculature: The ARIC Study.

Background The associations of time-averaged cumulative blood pressure (BP) from midlife to late life with microvasculature expressed as retinal vessel diameters is not well studied. The aim of this study was to evaluate the association of cumulative systolic BP and diastolic BP (DBP) with retinal vessel calibers, focusing on race differences. Methods and Results The analysis included 1818 adults from the ARIC (Atherosclerosis Risk in Communities) study attending the fifth visit (2011-2013; age 77±5 years, 17.1% Black participants). Time-averaged cumulative BPs were calculated as the sum of averaged BPs from adjacent consecutive visits (visits 1-5) indexed to total observation time (24±1 years). Summarized estimates for central retinal arteriolar equivalent and central retinal venular equivalent at the fifth visit represent average retinal vessel diameters. The arteriole:venule ratio was calculated. We tested for effect modification by race. Results from multiple linear regression models suggested that higher time-averaged cumulative DBP (ß [95% CI] per 1-SD increase: -1.78 [-2.53, -1.02], P<0.001 and -0.005 [-0.009, -0.002], P=0.004, respectively) but not systolic BP (-0.52 [-1.30, 0.26], P=0.189 and 0.001 [-0.002, 0.005], P=0.485, respectively) was associated with smaller central retinal arteriolar equivalent and arteriole:venule ratio. The association between time-averaged cumulative DBP and arteriole:venule ratio was strongest in White participants (interaction P=0.007). The association of cumulative systolic BP and DBP with central retinal venular equivalent was strongest in Black participants (interaction P=0.015 and 0.011, respectively). Conclusions Exposure to higher BP levels, particularly DBP, from midlife to late life is associated with narrower retinal vessel diameters in late life. Furthermore, race moderated the association of cumulative BP exposure with retinal microvasculature.

Luseogliflozin, a sodium-glucose cotransporter-2 inhibitor, reverses cerebrovascular dysfunction and cognitive impairments in 18-mo-old diabetic animals.

Diabetes mellitus (DM) is a leading risk factor for age-related dementia, but the mechanisms involved are not well understood. We previously discovered that hyperglycemia induced impaired myogenic response (MR) and cerebral blood flow (CBF) autoregulation in 18-mo-old DM rats associated with blood-brain barrier (BBB) leakage, impaired neurovascular coupling, and cognitive impairment. In the present study, we examined whether reducing plasma glucose with a sodium-glucose cotransporter-2 inhibitor (SGLT2i) luseogliflozin can ameliorate cerebral vascular and cognitive function in diabetic rats. Plasma glucose and HbA1c levels of 18-mo-old DM rats were reduced, and blood pressure was not altered after treatment with luseogliflozin. SGLT2i treatment restored the impaired MR of middle cerebral arteries (MCAs) and parenchymal arterioles and surface and deep cortical CBF autoregulation in DM rats. Luseogliflozin treatment also rescued neurovascular uncoupling, reduced BBB leakage and cognitive deficits in DM rats. However, SGLT2i did not have direct constrictive effects on vascular smooth muscle cells and MCAs isolated from normal rats, although it decreased reactive oxygen species production in cerebral vessels of DM rats. These results provide evidence that normalization of hyperglycemia with an SGLT2i can reverse cerebrovascular dysfunction and cognitive impairments in rats with long-standing hyperglycemia, possibly by ameliorating oxidative stress-caused vascular damage.NEW & NOTEWORTHY This study demonstrates that luseogliflozin, a sodium-glucose cotransporter-2 inhibitor, improved CBF autoregulation in association with reduced vascular oxidative stress and AGEs production in the cerebrovasculature of 18-mo-old DM rats. SGLT2i also prevented BBB leakage, impaired functional hyperemia, neurodegeneration, and cognitive impairment seen in DM rats. Luseogliflozin did not have direct constrictive effects on VSMCs and MCAs isolated from normal rats. These results provide evidence that normalization of hyperglycemia with an SGLT2i can reverse cerebrovascular dysfunction and cognitive impairments in rats with long-standing hyperglycemia, possibly by ameliorating oxidative stress-caused vascular damage.

Identification of cardiovascular high-risk groups from dynamic retinal vessel signals using untargeted machine learning.

AIMS: Dynamic retinal vessel analysis (DVA) provides a non-invasive way to assess microvascular function in patients and potentially to improve predictions of individual cardiovascular (CV) risk. The aim of our study was to use untargeted machine learning on DVA in order to improve CV mortality prediction and identify corresponding response alterations. METHODS AND RESULTS: We adopted a workflow consisting of noise reduction and extraction of independent components within DVA signals. Predictor performance was assessed in survival random forest models. Applying our technique to the prediction of all-cause mortality in a cohort of 214 haemodialysis patients resulted in the selection of a component which was highly correlated to maximal venous dilation following flicker stimulation (vMax), a previously identified predictor, confirming the validity of our approach. When fitting for CV mortality as the outcome of interest, a combination of three components derived from the arterial signal resulted in a marked improvement in predictive performance. Clustering analysis suggested that these independent components identified groups of patients with substantially higher CV mortality. CONCLUSION: Our results provide a machine learning workflow to improve the predictive performance of DVA and identify groups of haemodialysis patients at high risk of CV mortality. Our approach may also prove to be promising for DVA signal analysis in other CV disease states.

Tissue sodium content correlates with hypertrophic vascular remodeling in type 2 diabetes.

BACKGROUND: Prospective studies describe a linkage between increased sodium intake and higher incidence of cardiovascular organ damage and end points. We analyzed whether tissue sodium content in the skin and muscles correlate with vascular hypertrophic remodeling, a risk factor for cardiovascular disease. METHODS: In patients with type 2 diabetes we assessed tissue sodium content and vascular structural parameters of the retinal arterioles. The structural parameters of retinal arterioles assessed by Scanning Laser Doppler Flowmetry were vessel (VD) and lumen diameter (LD), wall thickness (WT), wall-to-lumen ratio (WLR) and wall cross sectional area (WCSA). Tissue sodium content was measured with a 3.0 T clinical 23Sodium-Magnetic Resonance Imaging (23Na-MRI) system. RESULTS: In patients with type 2 diabetes (N = 52) we observed a significant correlation between muscle sodium content and VD (p = 0.005), WT (p = 0.003), WCSA (p = 0.002) and WLR (p = 0.013). With respect to skin sodium content a significant correlation has been found with VD (p = 0.042), WT (p = 0.023) and WCSA (p = 0.019). Further analysis demonstrated that tissue sodium content of skin and muscle is a significant determinant of hypertrophic vascular remodeling independent of age, gender, diuretic use and 24-hour ambulatory BP. CONCLUSION: With the 23Na-MRI technology we could demonstrate that high tissue sodium content is independently linked to hypertrophic vascular remodeling in type 2 diabetes. TRIAL REGISTRATION: Trial registration number: NCT02383238 Date of registration: March 9, 2015.

Constrictor responses of cerebral resistance arterioles in male and female rats exposed to prenatal alcohol.

While it is known that dilation of cerebral arterioles to NOS-dependent agonists is impaired in rats exposed to prenatal alcohol, no studies have examined the influence of prenatal alcohol on constrictor response of cerebral arterioles. Our goal was to determine whether constrictor responses of cerebral resistance arterioles are altered by prenatal exposure to alcohol and if any changes differed as a function of age or sex. We fed Sprague-Dawley rat dams a liquid diet with or without alcohol (3% ethanol) for the duration of their pregnancy. We then examined reactivity of cerebral arterioles to thromboxane (U-46619; 0.01 and 0.1 µM), arginine vasopressin (0.1 and 1 nM), and angiotensin II (1 and 10 µM) in four groups of offspring: control male and female, and prenatal alcohol male and female at two different ages (adolescent: 4-6 weeks old and adult: 14-16 weeks old). Constriction of cerebral arterioles to U-46619 and AVP were similar in male and female rats regardless of exposure to prenatal alcohol and age. Similarly, adolescent male and female rats showed no difference to angiotensin II following prenatal exposure to alcohol. However, alcohol-exposed females exhibited an unexpected dilation to the high concentration of angiotensin II in adulthood, which was absent in males. We suggest that the findings from these studies may have implications regarding the susceptibility of the brain to cerebral ischemic damage. We speculate that impaired vasodilation, coupled with preserved vasoconstriction, can lead to a scenario favoring a decrease in cerebral blood flow during times of increased metabolic demand.

Retinal diffusion restrictions in acute branch retinal arteriolar occlusion.

This study sought to investigate the occurrence of retinal diffusion restrictions (RDR) in branch retinal arteriolar occlusion (BRAO) using standard brain diffusion-weighted imaging (DWI). Two radiologists assessed DWI MRI scans of BRAO patients for RDR in a retrospective cohort study. Inter- and intrarater reliability were calculated using Kappa statistics. Detection rates of RDR were compared among MRI scans with varying field strength, sequence type and onset-to-DWI time intervals. 85 BRAO patients (63.1 ± 16.5 years) and 89 DWI scans were evaluated. Overall sensitivity of RDR in BRAO was 46.1% with visually correlating low ADC signal in 56.1% of cases. Localization of RDR matched distribution of fundoscopic retinal edema in 85% of patients. Inter- and intra-rater agreement for RDR in BRAO was κinter = 0.64 (95% CI 0.48-0.80) and κintra = 0.87 (95% CI 0.76-0.96), respectively. RDR detection rate tended to be higher for 3T, when compared to 1.5T MRI scans (53.7% vs. 34.3%%; p = 0.07). RDR were identified within 24 h up to 2 weeks after onset of visual impairment. RDR in BRAO can be observed by means of standard stroke DWI in a substantial proportion of cases, although sensitivity and interrater reliability were lower than previously reported for complete central retinal artery occlusion.

Commentary on Intraglumerular dysfunction predicts kidney failure in the type 2 diabetes.

The key physiological parameters that determine glomerular filtration rate levels are renal plasma flow, filtration fraction, intraglomerular pressure, and balance between afferent and efferent glomerular arteriolar resistance. The evaluation of the balance between afferent and efferent glomerular arteriolar resistance might be useful for the classification of diabetic kidney disease.

Exercise training mitigates ER stress and UCP2 deficiency-associated coronary vascular dysfunction in atherosclerosis.

Endoplasmic reticulum (ER) stress and uncoupling protein-2 (UCP2) activation are opposing modulators of endothelial dysfunction in atherosclerosis. Exercise reduces atherosclerosis plaques and enhances endothelial function. Our aim was to understand how exercise affects ER stress and UCP2 activation, and how that relates to endothelial dysfunction in an atherosclerotic murine model. Wild type (C57BL/6, WT) and apolipoprotein-E-knockout (ApoEtm1Unc, ApoE KO) mice underwent treadmill exercise training (EX) or remained sedentary for 12 weeks. Acetylcholine (ACh)-induced endothelium-dependent vasodilation was determined in the presence of an eNOS inhibitor (L-NAME), UCP2 inhibitor (genipin), and ER stress inducer (tunicamycin). UCP2, ER stress markers and NLRP3 inflammasome signaling were quantified by western blotting. p67phox and superoxide were visualized using immunofluorescence and DHE staining. Nitric oxide (NO) was measured by nitrate/nitrite assay. ACh-induced vasodilation was attenuated in coronary arterioles of ApoE KO mice but improved in ApoE KO-EX mice. Treatment of coronary arterioles with L-NAME, tunicamycin, and genipin significantly attenuated ACh-induced vasodilation in all mice except for ApoE KO mice. Exercise reduced expression of ER stress proteins, TXNIP/NLRP3 inflammasome signaling cascades, and Bax expression in the heart of ApoE KO-EX mice. Further, exercise diminished superoxide production and NADPH oxidase p67phox expression in coronary arterioles while simultaneously increasing UCP2 expression and nitric oxide (NO) production in the heart of ApoE KO-EX mice. Routine exercise alleviates endothelial dysfunction in atherosclerotic coronary arterioles in an eNOS, UCP2, and ER stress signaling specific manner, and resulting in reduced TXNIP/NLRP3 inflammasome activity and oxidative stress.

Thomas Willis Lecture: Targeting Brain Arterioles for Acute Stroke Treatment.

Cerebral infarction or ischemic death of brain tissue, most notably neurons, is a primary response to vascular occlusion that if minimized leads to better stroke outcome. However, many cell types are affected in the brain during ischemia and reperfusion, including vascular cells of the cerebral circulation. Importantly, the structure and function of all brain vascular segments are major determinants of the depth of ischemia during the occlusion, the extent of collateral flow (and therefore amount of potentially salvageable tissue) and the degree of reperfusion. Thus, appropriate function of the cerebral circulation can influence stroke outcome. The brain vasculature is also directly involved in secondary injury to ischemia, including edema, hemorrhage, and infarct expansion, and provides a key delivery route for neuroprotective agents. Therefore, the cerebral circulation provides a therapeutic target for multiple aspects of stroke injury, including aiding neuroprotection. Understanding how ischemia and reperfusion affect the brain vasculature is key to this therapeutic potential, that is, vascular protection. This report is focused on regional differences in the cerebral circulation, how ischemia and reperfusion differentially affects these segments, and how the response of large versus small vessels in the brain to ischemia and reperfusion can influence stroke outcome. Last, how chronic hypertension, a common comorbidity in patients with stroke, affects the brain microvasculature to worsen stroke outcome will be described.

Rosiglitazone restores nitric oxide synthase-dependent reactivity of cerebral arterioles in rats exposed to prenatal alcohol.

BACKGROUND: Prenatal exposure to alcohol leads to a greater incidence of many cardiovascular-related diseases, presumably via a mechanism that may involve increased oxidative stress. An agonist of peroxisome proliferator-activated receptor gamma (PPARγ; rosiglitazone) has been shown to suppress alcohol-induced neuroinflammation and oxidative stress. The goal of this study was to determine whether acute and chronic treatment with rosiglitazone could restore or prevent impaired nitric oxide synthase (NOS)-dependent responses of cerebral arterioles in male and female adult (14-16 weeks old) rats exposed to alcohol in utero. METHODS: We fed Sprague-Dawley dams a liquid diet with or without 3% ethanol for the duration of their pregnancy (21-23 days). In the first series of studies, we examined the reactivity of cerebral arterioles to eNOS- (ADP), nNOS-dependent (NMDA), and NOS-independent agonists in male and female adult rats before and during acute (1 hour) topical application of rosiglitazone (1 µM). In a second series of studies, we examined the influence of chronic treatment with rosiglitazone (3 mg/kg/day in drinking water for 2-3 weeks) on the responses of cerebral arterioles in male and female adult rats exposed to alcohol in utero. RESULTS: We found that in utero exposure to alcohol similarly reduced responses of cerebral arterioles to ADP and NMDA, but not to nitroglycerin in male and female adult rats. In addition, acute treatment of the male and female adult rats with rosiglitazone similarly restored this impairment in cerebral vascular function to that observed in controls. We also found that chronic treatment with rosiglitazone prevented impaired vascular function in male and female adult rats that were exposed to alcohol in utero. CONCLUSIONS: PPARγ activation may be an effective and relevant treatment to reverse or prevent cerebral vascular abnormalities associated with prenatal exposure to alcohol.

Mineralocorticoid receptor blockade normalizes coronary resistance in obese swine independent of functional alterations in Kv channels.

Impaired coronary microvascular function (e.g., reduced dilation and coronary flow reserve) predicts cardiac mortality in obesity, yet underlying mechanisms and potential therapeutic strategies remain poorly understood. Mineralocorticoid receptor (MR) antagonism improves coronary microvascular function in obese humans and animals. Whether MR blockade improves in vivo regulation of coronary flow, a process involving voltage-dependent K+ (Kv) channel activation, or reduces coronary structural remodeling in obesity is unclear. Thus, the goals of this investigation were to determine the effects of obesity on coronary responsiveness to reductions in arterial PO2 and potential involvement of Kv channels and whether the benefit of MR blockade involves improved coronary Kv function or altered passive structural properties of the coronary microcirculation. Hypoxemia increased coronary blood flow similarly in lean and obese swine; however, baseline coronary vascular resistance was significantly higher in obese swine. Inhibition of Kv channels reduced coronary blood flow and augmented coronary resistance under baseline conditions in lean but not obese swine and had no impact on hypoxemic coronary vasodilation. Chronic MR inhibition in obese swine normalized baseline coronary resistance, did not influence hypoxemic coronary vasodilation, and did not restore coronary Kv function (assessed in vivo, ex vivo, and via patch clamping). Lastly, MR blockade prevented obesity-associated coronary arteriolar stiffening independent of cardiac capillary density and changes in cardiac function. These data indicate that chronic MR inhibition prevents increased coronary resistance in obesity independent of Kv channel function and is associated with mitigation of obesity-mediated coronary arteriolar stiffening.

Differential responses of resistance arterioles to elevated intraluminal pressure in blacks and whites.

Black Americans have an earlier onset, higher average blood pressure, and higher rates of hypertension-related mortality and morbidity, compared to whites. The racial difference may be related to microvasculature, the major regulatory site of blood pressure. The goal of this study was to compare the response of resistance vessels to high intraluminal pressure between black and white participants. A total of 38 vessels were obtained from human fat samples [21 black, 17 white; mean age 32 ± 12 yr and body mass index (BMI) 26.9 ± 4.9; between-group P ≥ 0.05] and included in this study. Internal diameter was measured in response to the flow induced by various pressure gradients (Δ10, Δ20, Δ40, Δ60, and Δ100 cmH2O), and flow-induced dilation (FID) was calculated before and after high intraluminal pressure (150 cmH2O). Before high intraluminal pressure, FID was not different between blacks and whites (P = 0.112). After exposure to high intraluminal pressure, FID was reduced at every pressure gradient in vessels from blacks (P < 0.001), whereas FID did not change in white participants except at Δ100 cmH2O. When incubated with the hydrogen peroxide (H2O2) scavenger polyethylene glycol-catalase (PEG-catalase), the FID response in vessels from black, but not white, individuals was significantly reduced and the magnitude was higher at normal pressure relative to high pressure. Our findings suggest that the vessels from self-identified black individuals are more susceptible to microvascular dysfunction following transient periods of high intraluminal pressure compared to whites and show greater dependence on H2O2 as a main contributor to FID at normal pressures.NEW & NOTEWORTHY Microvascular function regulates blood pressure and may contribute to racial differences in the incidence and prevalence of hypertension and other cardiovascular diseases. Here, we show that using an ex vivo model of resistance arterioles isolated from human gluteal fat tissue, flow-induced dilation is not different between black and white participants. However, when exposed to transient increases in intraluminal pressure, the flow-induced dilation in resistance arterioles from black participants demonstrated greater reductions relative to their white counterparts, indicating a higher sensitivity to pressure change in the microvasculature.

The cold receptor TRPM8 activation leads to attenuation of endothelium-dependent cerebral vascular functions during head cooling.

Using the cranial window technique, we investigated acute effects of head cooling on cerebral vascular functions in newborn pigs. Head cooling lowered the rectal and extradural brain temperatures to 34.3 ± 0.6°C and 26.1 ± 0.6°C, respectively. During the 3-h hypothermia period, responses of pial arterioles to endothelium-dependent dilators bradykinin and glutamate were reduced, whereas the responses to hypercapnia and an endothelium-independent dilator sodium nitroprusside (SNP) remained intact. All vasodilator responses were restored after rewarming, suggesting that head cooling did not produce endothelial injury. We tested the hypothesis that the cold-sensitive TRPM8 channel is involved in attenuation of cerebrovascular functions. TRPM8 is immunodetected in cerebral vessels and in the brain parenchyma. During normothermia, the TRPM8 agonist icilin produced constriction of pial arterioles that was antagonized by the channel blocker AMTB. Icilin reduced dilation of pial arterioles to bradykinin and glutamate but not to hypercapnia and SNP, thus mimicking the effects of head cooling on vascular functions. AMTB counteracted the impairment of endothelium-dependent vasodilation caused by hypothermia or icilin. Overall, mild hypothermia produced by head cooling leads to acute reversible reduction of selected endothelium-dependent cerebral vasodilator functions via TRPM8 activation, whereas cerebral arteriolar smooth muscle functions are largely preserved.