A Pilot Study Examining the Effects of Ischemic Conditioning on Walking Capacity and Lower Extremity Muscle Performance in Patients with Claudication.

INTRODUCTION: This study investigated whether a novel therapy called ischemic conditioning (IC) improves walking capacity and lower extremity muscle performance in patients with peripheral vascular disease who experience intermittent claudication. METHODS: Forty-three patients with claudication were enrolled and received either IC or IC Sham for 2 weeks in this randomized, controlled, double-blinded, prospective study. IC sessions involved five cycles of alternating 5-min inflations of a blood pressure cuff to 225 mm Hg (25 mm Hg for IC Sham) and 5-min deflations, around the thigh of the affected lower extremity. RESULTS: There was no difference in the change in claudication onset time (Δ = 114 ± 212 s IC vs. 104 ± 173 s IC Sham; p = 0.67) or peak walking time (Δ = 42 ± 139 s IC vs. 12 ± 148 s IC Sham; p = 0.35) between the IC and IC Sham groups. At the level of the knee, participants in the IC group performed more work (Δ = 3,029 ± 4,999 J IC vs. 345 ± 2,863 J IC Sham; p = 0.03) and displayed a greater time to muscle fatigue (Δ = 147 ± 221 s IC vs. -27 ± 236 s IC Sham; p = 0.01). DISCUSSION/CONCLUSION: In patients with claudication, IC improved total work performed and time to fatigue at the knee but did not change walking parameters.

BCR-ABL tyrosine kinase inhibitors promote pathological changes in dilator phenotype in the human microvasculature.

OBJECTIVE: Treatment with BCR-ABL tyrosine kinase inhibitors (TKIs) is the standard of care for patients with chronic myeloid leukemia, however evidence indicates these compounds may have cardiovascular side-effects. This study sought to determine if ex vivo exposure of human adipose arterioles to the BCR-ABL TKIs imatinib and nilotinib causes endothelial dysfunction. METHODS: Human adipose arterioles were incubated overnight in cell culture media containing vehicle (PBS), imatinib (10 µmol/L) or nilotinib (100 µmol/L). Arterioles were cannulated onto glass pipettes and flow mediated dilation (FMD) was assessed via video microscopy. To determine the mechanism of vasodilation, FMD was re-assessed in the presence of either the nitric oxide synthase inhibitor L-NAME (100 µmol/L) or the H2 O2 scavenger PEG-Catalase (500 U/mL). RESULTS: Neither imatinib nor nilotinib affected the magnitude of FMD (max dilation = 78±17% vehicle, 80 ± 24% nilotinib, 73 ± 13% imatinib). FMD was decreased by L-NAME in vehicle-treated arterioles (max dilation = 47±29%). Conversely, L-NAME had no effect on FMD in imatinib- or nilotinib-treated vessels (max dilation = 79±14% and 80 ± 24%, respectively), rather FMD was inhibited by PEG-Catalase (max dilation = 29±11% and 29 ± 14%, respectively). CONCLUSION: Incubating human arterioles with imatinib or nilotinib switches the mediator of FMD from vasoprotective nitric oxide to pro-inflammatory H2 O2 .

The Human Microcirculation: Regulation of Flow and Beyond.

The microcirculation is responsible for orchestrating adjustments in vascular tone to match local tissue perfusion with oxygen demand. Beyond this metabolic dilation, the microvasculature plays a critical role in modulating vascular tone by endothelial release of an unusually diverse family of compounds including nitric oxide, other reactive oxygen species, and arachidonic acid metabolites. Animal models have provided excellent insight into mechanisms of vasoregulation in health and disease. However, there are unique aspects of the human microcirculation that serve as the focus of this review. The concept is put forth that vasculoparenchymal communication is multimodal, with vascular release of nitric oxide eliciting dilation and preserving normal parenchymal function by inhibiting inflammation and proliferation. Likewise, in disease or stress, endothelial release of reactive oxygen species mediates both dilation and parenchymal inflammation leading to cellular dysfunction, thrombosis, and fibrosis. Some pathways responsible for this stress-induced shift in mediator of vasodilation are proposed. This paradigm may help explain why microvascular dysfunction is such a powerful predictor of cardiovascular events and help identify new approaches to treatment and prevention.

Critical Role for Telomerase in the Mechanism of Flow-Mediated Dilation in the Human Microcirculation.

RATIONALE: Telomerase is a nuclear regulator of telomere elongation with recent reports suggesting a role in regulation of mitochondrial reactive oxygen species. Flow-mediated dilation in patients with cardiovascular disease is dependent on the formation of reactive oxygen species. OBJECTIVE: We examined the hypothesis that telomerase activity modulates microvascular flow-mediated dilation, and loss of telomerase activity contributes to the change of mediator from nitric oxide to mitochondrial hydrogen peroxide in patients with coronary artery disease (CAD). METHODS AND RESULTS: Human coronary and adipose arterioles were isolated for videomicroscopy. Flow-mediated dilation was measured in vessels pretreated with the telomerase inhibitor BIBR-1532 or vehicle. Statistical differences between groups were determined using a 2-way analysis of variance repeated measure (n≥4; P<0.05). L-NAME (N(ω)-nitro-L-arginine methyl ester; nitric oxide synthase inhibitor) abolished flow-mediated dilation in arterioles from subjects without CAD, whereas polyethylene glycol-catalase (PEG-catalase; hydrogen peroxide scavenger) had no effect. After exposure to BIBR-1532, arterioles from non-CAD subjects maintained the magnitude of dilation but changed the mediator from nitric oxide to mitochondrial hydrogen peroxide (% max diameter at 100 cm H2O: vehicle 74.6±4.1, L-NAME 37.0±2.0*, PEG-catalase 82.1±2.8; BIBR-1532 69.9±4.0, L-NAME 84.7±2.2, PEG-catalase 36.5±6.9*). Conversely, treatment of microvessels from CAD patients with the telomerase activator AGS 499 converted the PEG-catalase-inhibitable dilation to one mediated by nitric oxide (% max diameter at 100 cm H2O: adipose, AGS 499 78.5±3.9; L-NAME 10.9±17.5*; PEG-catalase 79.2±4.9). Endothelial-independent dilation was not altered with either treatment. CONCLUSIONS: We have identified a novel role for telomerase in re-establishing a physiological mechanism of vasodilation in arterioles from subjects with CAD. These findings suggest a new target for reducing the oxidative milieu in the microvasculature of patients with CAD.

Mitochondria-regulated formation of endothelium-derived extracellular vesicles shifts the mediator of flow-induced vasodilation.

To examine the effect of endothelium-derived extracellular vesicles (eEVs) on the mediator of flow-induced dilation (FID), composition, formation, and functional effects on the mediator of FID were examined from two different eEV subtypes, one produced from ceramide, while the other was produced from plasminogen-activator inhibitor 1 (PAI-1). Using video microscopy, we measured internal-diameter changes in response to increases in flow in human adipose resistance arteries acutely exposed (30 min) to eEVs derived from cultured endothelial cells exposed to ceramide or PAI-1. FID was significantly impaired following exposure to 500K/ml (K = 1,000) of ceramide-induced eEVs (Cer-eEVs) but unaffected by 250K/ml. FID was reduced in the presence of PEG-catalase following administration of 250K/ml of Cer-eEVs and PAI-1 eEVs, whereas Nω-nitro-l-arginine methyl ester (l-NAME) had no effect. Pathway analysis following protein composition examination using liquid chromatography tandem mass spectrometry (LC-MS/MS) demonstrated that both subtypes were strongly linked to similar biological functions, primarily, mitochondrial dysfunction. Flow cytometry was used to quantify eEVs in the presence or absence of l-phenylalanine-4'-boronic acid (PBA) and mitochondria-targeted [93-boronophenyl)methyl]triphenyl-phosphonium (mito-PBA), cytosolic and mitochondrial-targeted antioxidants, respectively. eEV formation was significantly and dramatically reduced with mito-PBA treatment. In conclusion, eEVs have a biphasic effect, with higher doses impairing and lower doses shifting the mediator of FID from nitric oxide (NO) to hydrogen peroxide (H2O2). Despite differences in protein content, eEVs may alter vascular function in similar directions, regardless of the stimulus used for their formation. Furthermore, mitochondrial ROS production is required for the generation of these vesicles.NEW & NOTEWORTHY The vascular effect of endothelium-derived extracellular vesicles (eEVs) is biphasic, with higher doses decreasing the magnitude of flow-induced dilation (FID) compared with lower doses that shift the mediator of FID from nitric oxide to H2O2 eEVs may cause vascular dysfunction via similar pathways despite being formed from different stimuli, although both require mitochondrial reactive oxygen species for their formation.

Vascular Actions of Angiotensin 1-7 in the Human Microcirculation: Novel Role for Telomerase.

OBJECTIVE: This study examined vascular actions of angiotensin 1-7 (ANG 1-7) in human atrial and adipose arterioles. APPROACH AND RESULTS: The endothelium-derived hyperpolarizing factor of flow-mediated dilation (FMD) switches from antiproliferative nitric oxide (NO) to proatherosclerotic hydrogen peroxide in arterioles from humans with coronary artery disease (CAD). Given the known vasoprotective properties of ANG 1-7, we tested the hypothesis that overnight ANG 1-7 treatment restores the NO component of FMD in arterioles from patients with CAD. Endothelial telomerase activity is essential for preserving the NO component of vasodilation in the human microcirculation; thus, we also tested whether telomerase activity was necessary for ANG 1-7-mediated vasoprotection by treating separate arterioles with ANG 1-7±the telomerase inhibitor 2-[[(2E)-3-(2-naphthalenyl)-1-oxo-2-butenyl1-yl]amino]benzoic acid. ANG 1-7 dilated arterioles from patients without CAD, whereas dilation was significantly reduced in arterioles from patients with CAD. In atrial arterioles from patients with CAD incubated with ANG 1-7 overnight, the NO synthase inhibitor NG-nitro-l-arginine methyl ester abolished FMD, whereas the hydrogen peroxide scavenger polyethylene glycol catalase had no effect. Conversely, in vessels incubated with ANG 1-7+2-[[(2E)-3-(2-naphthalenyl)-1-oxo-2-butenyl1-yl]amino]benzoic acid, NG-nitro-l-arginine methyl ester had no effect on FMD, but polyethylene glycol catalase abolished dilation. In cultured human coronary artery endothelial cells, ANG 1-7 significantly increased telomerase activity. These results indicate that ANG 1-7 dilates human microvessels, and dilation is abrogated in the presence of CAD. Furthermore, ANG 1-7 treatment is sufficient to restore the NO component of FMD in arterioles from patients with CAD in a telomerase-dependent manner. CONCLUSIONS: ANG 1-7 exerts vasoprotection in the human microvasculature via modulation of telomerase activity.

An acute rise in intraluminal pressure shifts the mediator of flow-mediated dilation from nitric oxide to hydrogen peroxide in human arterioles.

Endothelial nitric oxide (NO) is the primary mediator of flow-mediated dilation (FMD) in human adipose microvessels. Impaired NO-mediated vasodilation occurs after acute and chronic hypertension, possibly due to excess generation of reactive oxygen species (ROS). The direct role of pressure elevation in this impairment of human arteriolar dilation is not known. We tested the hypothesis that elevation in pressure is sufficient to impair FMD. Arterioles were isolated from human adipose tissue and cannulated, and vasodilation to graded flow gradients was measured before and after exposure to increased intraluminal pressure (IILP; 150 mmHg, 30 min). The mediator of FMD was determined using pharmacological agents to reduce NO [N(G)-nitro-l-arginine methyl ester (l-NAME), 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO)], or H2O2 [polyethylene glycol (PEG)-catalase], and mitochondrial (mt) ROS was quantified using fluorescence microscopy. Exposure to IILP decreased overall FMD (max %dilation: 82.7 ± 4.9 vs. 62 ± 5.6; P < 0.05). This dilation was abolished by treatment with l-NAME prepressure and PEG-catalase after IILP (max %dilation: l-NAME: 23.8 ± 6.1 vs. 74.8 ± 8.6; PEG-catalase: 71.8 ± 5.9 vs. 24.6 ± 10.6). To examine if this change was mediated by mtROS, FMD responses were measured in the presence of the complex I inhibitor rotenone or the mitochondrial antioxidant mitoTempol. Before IILP, FMD was unaffected by either compound; however, both inhibited dilation after IILP. The fluorescence intensity of mitochondria peroxy yellow 1 (MitoPY1), a mitochondria-specific fluorescent probe for H2O2, increased during flow after IILP (%change from static: 12.3 ± 14.5 vs. 127.9 ± 57.7). These results demonstrate a novel compensatory dilator mechanism in humans that is triggered by IILP, inducing a change in the mediator of FMD from NO to mitochondria-derived H2O2.

The vascular renin-angiotensin system contributes to blunted vasodilation induced by transient high pressure in human adipose microvessels.

Increased intraluminal pressure can reduce endothelial function in resistance arterioles; however, the mechanism of this impairment is unknown. The purpose of this study was to determine the effect of local renin-angiotensin system inhibition on the pressure-induced blunting of endothelium-dependent vasodilation in human adipose arterioles. Arterioles (100-200 µm) were dissected from fresh adipose surgical specimens, cannulated onto glass micropipettes, pressurized to an intraluminal pressure of 60 mmHg, and constricted with endothelin-1. Vasodilation to ACh was assessed at 60 mmHg and again after a 30-min exposure to an intraluminal pressure of 150 mmHg. The vasodilator response to ACh was significantly reduced in vessels exposed to 150 mmHg. Exposure of the vessels to the superoxide scavenger polyethylene glycol-SOD (100 U/ml), the ANG II type 1 receptor antagonist losartan (10(-6) mol/l), or the angiotensin-converting enzyme inhibitor captopril (10(-5) mol/l) prevented the pressure-induced reduction in ACh-dependent vasodilation observed in untreated vessels. High intraluminal pressure had no effect on papaverine-induced vasodilation or ANG II sensitivity. Increased intraluminal pressure increased dihydroethidium fluorescence in cannulated vessels, which could be prevented by polyethylene glycol-SOD or losartan treatment and endothelial denudation. These data indicate that high intraluminal pressure can increase vascular superoxide and reduce nitric oxide-mediated vasodilation via activation of the vascular renin-angiotensin system. This study provides evidence showing that the local renin-angiotensin system in the human microvasculature may be pressure sensitive and contribute to endothelial dysfunction after acute bouts of hypertension.

Exercise and vascular function: how much is too much?

Exercise is a powerful therapy for preventing the onset of and slowing the progression of cardiovascular disease. Increased shear stress during exercise improves vascular homeostasis by both decreasing reactive oxygen species and increasing nitric oxide bioavailability in the endothelium. While these observations are well accepted as they apply to individuals at risk for cardiovascular disease, less is known about how exercise, especially intense exercise, affects vascular function in healthy individuals. This review highlights examples of how vascular function can paradoxically be impaired in otherwise healthy individuals by extreme levels of exercise, with a focus on the causative role that reactive oxygen species play in this impairment.

Non-Invasive Estimation of Skeletal Muscle Oxygen Consumption Rate and Microvascular Reactivity in Chronic Stroke Survivors using Near Infrared Spectroscopy.

BACKGROUND: Understanding post-stroke changes in skeletal muscle oxidative metabolism and microvascular reactivity could help create therapeutic targets that optimize rehabilitative interventions. Due to disuse atrophy, we hypothesized that basal muscle oxygen consumption rate and microvascular endothelial function would be impaired in the tibialis anterior (TA) muscle of the affected leg of chronic stroke survivors compared to the non-affected leg and vs. matched controls. METHODS: Fifteen chronic stroke survivors (10 female) and 15 matched controls (9 female) completed this study. A near infrared spectroscopy oximeter measured tissue oxygen saturation (StO2) of the TA in both legs of stroke survivors and the dominant leg of controls. A cuff was placed around the thigh and inflated to 225 mmHg for five minutes while StO2 was continuously measured. The rate of change in StO2 was calculated during cuff occlusion and immediately post-cuff release. RESULTS: The rate of oxygen desaturation was similar between the legs of the stroke survivors (paretic -0.12±0.04 %∙s-1 vs non-paretic -0.16±011 %∙s-1; p=0.49), but the paretic leg had a reduced desaturation rate vs. controls (-0.25±0.18%∙s-1; p=0.007 vs. paretic leg). After cuff release, there was a greater oxygen resaturation rate in the non-paretic leg compared to the paretic leg (3.13±2.08 %∙s-1 vs. 1.60±1.11 %∙s-1, respectively; p=0.01). The control leg had a similar resaturation rate vs. the non-paretic leg (control = 3.41±1.79%∙s-1; p=0.69) but was greater than the paretic leg (p=0.003). CONCLUSION: The TA in the paretic leg had an impaired muscle oxygen consumption rate and reduced microvascular endothelial function compared to controls.

Diversity in mechanisms of endothelium-dependent vasodilation in health and disease.

Small arterioles (40-150 µm) contribute to the majority of vascular resistance within organs and tissues. Under resting conditions, the basal tone of these vessels is determined by a delicate balance between vasodilator and vasoconstrictor influences. Cardiovascular homeostasis and regional tissue perfusion is largely a function of the ability of these small blood vessels to constrict or dilate in response to the changing metabolic demands of specific tissues. The endothelial cell layer of these microvessels is a key modulator of vasodilation through the synthesis and release of vasoactive substances. Beyond their vasomotor properties, these compounds importantly modulate vascular cell proliferation, inflammation, and thrombosis. Thus, the balance between local regulation of vascular tone and vascular pathophysiology can vary depending upon which factors are released from the endothelium. This review will focus on the dynamic nature of the endothelial released dilator factors depending on species, anatomic site, and presence of disease, with a focus on the human coronary microcirculation. Knowledge how endothelial signaling changes with disease may provide insights into the early stages of developing vascular inflammation and atherosclerosis, or related vascular pathologies.

Reduced oxygen desaturation in the vastus lateralis of chronic stroke survivors during graded muscle contractions.

BACKGROUND: Few studies have examined changes in skeletal muscle physiology post-stroke. This study examined changes in tissue oxygen saturation (StO2) of the vastus lateralis (VL) muscle of stroke survivors and age-matched control participants during maximal and submaximal isometric contractions of the knee extensor muscles. OBJECTIVES: We hypothesized that tissue oxygen desaturation (ΔStO2) during knee extensor muscle contractions would be less in the VL in the paretic vs. the non-paretic and control legs. METHODS: Ten chronic stroke survivors (>6 months post-stroke) with lower extremity muscle weakness and 10 age-matched controls completed this prospective cohort study. Maximum voluntary contractions (MVCs) of the knee extensor muscles were assessed with a Biodex dynamometer and StO2 of the VL was measured using near-infrared spectroscopy. RESULTS: In the paretic leg of the stroke survivors little change in StO2 of the VL was observed during an MVC (ΔStO2 = -1.7 ± 1.8%) compared to the non-paretic (ΔStO2 = -5.1 ± 6.1%; p < 0.05) and control legs (ΔStO2 = -14.4 ± 8.8%; p < 0.05 vs. paretic and non-paretic leg). These differences remained when normalizing for strength differences between the legs. Compared to controls, both the paretic and non-paretic VL showed pronounced reductions in ΔStO2 during ramp and hold contractions equal to 20%, 40%, or 60% of the MVC (p < 0.05 vs. controls at all load levels). CONCLUSIONS: These results indicate that oxygen desaturation in response to isometric muscle contractions is impaired in both the paretic and non-paretic leg muscle of stroke survivors compared to age-matched controls, and these differences are independent of differences in muscle strength.

Quantification of Tissue Oxygen Saturation in the Vastus Lateralis Muscle of Chronic Stroke Survivors during a Graded Exercise Test.

Purpose: This study examined tissue oxygen saturation (StO2) of the vastus lateralis (VL) muscles of chronic stroke survivors during a graded exercise test (GXT). We hypothesized the reduction in StO2 will be blunted in the paretic vs. non-paretic VL during a maximum-effort GXT. Methods: Chronic stroke survivors performed a GXT and StO2 of the VL in each leg was measured using near infrared spectroscopy. Twenty-six stroke survivors performed a GXT. Results: At rest, there was no difference in StO2 between the paretic and non-paretic VL (65±9% vs. 68±7%, respectively, p=0.32). The maximum change in StO2 from rest during the GXT was greater in the non-paretic vs. the paretic VL (-16±14% vs. -9±10%, respectively, p<0.001). The magnitude of the oxygen resaturation response was also greater in the non-paretic vs. the paretic VL (29±23% vs. 18±15%, respectively, p<0.001). VO2 Peak was associated with the magnitude of the VL StO2 change during (r2=0.54, p<0.0001) and after (r2=0.56, p<0.001) the GXT. Conclusions: During a GXT there is a blunted oxygen desaturation response in the paretic vs. the non-paretic VL of chronic stroke survivors. In the paretic VL there was a positive correlation between the oxygen desaturation response during the GXT and VO2 Peak.

Acute and chronic angiotensin-(1-7) restores vasodilation and reduces oxidative stress in mesenteric arteries of salt-fed rats.

This study determined the effect of ANG-(1-7) on salt-induced suppression of endothelium-dependent vasodilatation in the mesenteric arteries of male Sprague-Dawley rats. Chronic intravenous infusion of ANG-(1-7), oral administration of the nonpeptide mas receptor agonist AVE-0991, and acute preincubation of the arteries with ANG-(1-7) and AVE-0991 all restored vasodilator responses to both ACh and histamine that were absent in the arteries of rats fed a high-salt (4% NaCl) diet. The protective effects of ANG-(1-7) and AVE-0991 were inhibited by acute or chronic administration of the mas receptor antagonist A-779, the ANG II type 2 (AT(2)) receptor blocker PD-123319, or N-nitro-l-arginine methyl ester, but not the ANG II type 1 receptor antagonist losartan. Preincubation with the antioxidant tempol or the nitric oxide (NO) donor diethylenetriamine NONOate and acute and chronic administration of the AT(2) receptor agonist CGP-42112 mimicked the protective effect of ANG-(1-7) to restore vascular relaxation. Acute preincubation with ANG-(1-7) and chronic infusion of ANG-(1-7) ameliorated the elevated superoxide levels in rats fed a high-salt diet, but the expression of Cu/Zn SOD and Mn SOD enzyme proteins in the vessel wall was unaffected by ANG-(1-7) infusion. These results indicate that both acute and chronic systemic administration of ANG-(1-7) or AVE-0991 restore endothelium-dependent vascular relaxation in salt-fed Sprague-Dawley rats by reducing vascular oxidant stress and enhancing NO availability via mas and AT(2) receptors. These findings suggest a therapeutic potential for mas/AT(2) receptor activation in preventing the vascular oxidant stress and endothelial dysfunction associated with elevated dietary salt intake.

Pain relief following genicular nerve radiofrequency ablation: does knee compartment matter?

Aim: To investigate the effect of knee osteoarthritis (OA) compartment location on pain relief following genicular radiofrequency ablation. Materials & methods: A retrospective chart review was performed on 62 patients. Visual analog scale scores at 3 and 6 months post procedure were compared with baseline and between compartment groups. Results: Pain significantly improved for all patients at 3 and 6 months (p < 0.001 and p = 0.005, respectively). Medial compartment OA was a significant predictor of improvement at 3 months (p = 0.042). Patellofemoral compartment OA was a significant predictor for a higher visual analog scale at 3 months (p = 0.018). Conclusion: Compartmental location of knee OA impacts pain relief following genicular radiofrequency ablation. Future protocols could target nerves based on which compartments are more affected on imaging.

Lay abstract Aim: To investigate the effect of knee arthritis location on pain relief following planned nerve disruption using radiofrequency ablation (RFA). Materials & methods: This study analyzed existing records of 62 cases of patients who underwent an ablation procedure to the sensory nerves of the knee. On a scale from one to ten, pain after RFA at 3 and 6 months was compared with baseline and compared between arthritis location groups. Results: Pain decreased for all patients at 3 and 6 months. Inner knee arthritis was a predictor of pain improvement at 3 months. Arthritis of the kneecap was a predictor for worse pain at 3 months. Conclusion: Location of knee arthritis impacts pain relief following nerve disruption using RFA. Future protocols could target nerves based on arthritis location.

Angiotensin-(1-7) and low-dose angiotensin II infusion reverse salt-induced endothelial dysfunction via different mechanisms in rat middle cerebral arteries.

The goals of this study were to 1) determine the acute effect of ANG-(1-7) on vascular tone in isolated middle cerebral arteries (MCAs) from Sprague-Dawley rats fed a normal salt (NS; 0.4% NaCl) diet, 2) evaluate the ability of chronic intravenous infusion of ANG-(1-7) (4 ng·kg(-1)·min(-1)) for 3 days to restore endothelium-dependent dilation to acetylcholine (ACh) in rats fed a high-salt (HS; 4% NaCl) diet, and 3) determine whether the amelioration of endothelial dysfunction by ANG-(1-7) infusion in rats fed a HS diet is different from the protective effect of low-dose ANG II infusion in salt-fed rats. MCAs from rats fed a NS diet dilated in response to exogenous ANG-(1-7) (10(-10)-10(-5) M). Chronic ANG-(1-7) infusion significantly reduced vascular superoxide levels and restored the nitric oxide-dependent dilation to ACh (10(-10)-10(-5) M) that was lost in MCAs of rats fed a HS diet. Acute vasodilation to ANG-(1-7) and the restoration of ACh-induced dilation by chronic ANG-(1-7) infusion in rats fed a HS diet were blocked by the Mas receptor antagonist [D-ALA(7)]-ANG-(1-7) or the ANG II type 2 receptor antagonist PD-123319 and unaffected by ANG II type 1 receptor blockade with losartan. The restoration of ACh-induced dilation in MCAs of HS-fed rats by chronic intravenous infusion of ANG II (5 ng·kg(-1)·min(-1)) was blocked by losartan and unaffected by d-ALA. These findings demonstrate that circulating ANG-(1-7), working via the Mas receptor, restores endothelium-dependent vasodilation in cerebral resistance arteries of animals fed a HS diet via mechanisms distinct from those activated by low-dose ANG II infusion.

Impaired relaxation of cerebral arteries in the absence of elevated salt intake in normotensive congenic rats carrying the Dahl salt-sensitive renin gene.

This study evaluated endothelium-dependent vascular relaxation in response to acetylcholine (ACh) in isolated middle cerebral arteries (MCA) from Dahl salt-sensitive (Dahl SS) rats and three different congenic strains that contain a portion of Brown Norway (BN) chromosome 13 introgressed onto the Dahl SS genetic background through marker-assisted breeding. Two of the congenic strains carry a 3.5-Mbp portion and a 2.6-Mbp portion of chromosome 13 that lie on opposite sides of the renin locus, while the third contains a 2.0-Mbp overlapping region that includes the BN renin allele. While maintained on a normal salt (0.4% NaCl) diet, MCAs from Dahl SS rats and the congenic strains retaining the Dahl SS renin allele failed to dilate in response to ACh, whereas MCAs from the congenic strain carrying the BN renin allele exhibited normal vascular relaxation. In congenic rats receiving the BN renin allele, vasodilator responses to ACh were eliminated by nitric oxide synthase inhibition with N(G)-nitro-l-arginine methyl ester, angiotensin-converting enzyme inhibition with captopril, and AT(1) receptor blockade with losartan. N(G)-nitro-l-arginine methyl ester-sensitive vasodilation in response to ACh was restored in MCAs of Dahl SS rats that received either a 3-day infusion of a subpressor dose of angiotensin II (3 ng·kg(-1)·min(-1) iv), or chronic treatment with the superoxide dismutase mimetic tempol (15 mg·kg(-1)·day(-1)). These findings indicate that the presence of the Dahl SS renin allele plays a crucial role in endothelial dysfunction present in the cerebral circulation of the Dahl SS rat, even in the absence of elevated dietary salt intake, and that introgression of the BN renin allele rescues endothelium-dependent vasodilator responses by restoring normal activation of the renin-angiotensin system.

Comparing pain relief and functional improvement between methylprednisolone and dexamethasone lumbosacral transforaminal epidural steroid injections: a self-controlled study.

BACKGROUND: Previous studies have shown varying results between lumbosacral transforaminal epidural steroid injections (TFESIs) performed with particulate versus non-particulate corticosteroids. The purpose of this study was to investigate the difference in pain relief and functional improvement between particulate and non-particulate lumbosacral TFESIs in patients who had undergone both injections, sequentially. METHODS: This was a self-controlled, retrospective study of 20 patients who underwent both a methylprednisolone and a dexamethasone TFESI to the same vertebral level and side. Primary outcomes included pain relief according to the visual analogue scale (VAS) and functional improvement determined by a yes/no answer to questions regarding mobility and the activities of daily living. Post-injection data was recorded at 2, 3, and 6 months. RESULTS: A decrease in VAS scores of -3.4 ± 3.0 (mean ± standard deviation), -3.1 ± 3.1, and -2.8 ± 3.4 was seen for the methylprednisolone group at 2, 3, and 6 months, respectively. Similar decreases of -3.9 ± 3.5, -3.4 ± 2.8, and -2.3 ± 3.4 were seen in the dexamethasone group. There was no significant difference in pain relief at any point between the two medications. The percentage of subjects who reported improved function at 2, 3, and 6 months was 65%, 51%, and 41%, respectively, for the methylprednisolone group and 75%, 53%, and 42% for the dexamethasone group. CONCLUSIONS: These findings support the use of non-particulate corticosteroids for lumbosacral TFESIs in the context of documented safety concerns with particulate corticosteroids.