A GTPase-activating protein-binding protein (G3BP1)/antiviral protein relay conveys arteriosclerotic Wnt signals in aortic smooth muscle cells.

In aortic vascular smooth muscle (VSM), the canonical Wnt receptor LRP6 inhibits protein arginine (Arg) methylation, a new component of noncanonical Wnt signaling that stimulates nuclear factor of activated T cells (viz NFATc4). To better understand how methylation mediates these actions, MS was performed on VSM cell extracts from control and LRP6-deficient mice. LRP6-dependent Arg methylation was regulated on >500 proteins; only 21 exhibited increased monomethylation (MMA) with concomitant reductions in dimethylation. G3BP1, a known regulator of arteriosclerosis, exhibited a >30-fold increase in MMA in its C-terminal domain. Co-transfection studies confirm that G3BP1 (G3BP is Ras-GAP SH3 domain-binding protein) methylation is inhibited by LRP6 and that G3BP1 stimulates NFATc4 transcription. NFATc4 association with VSM osteopontin (OPN) and alkaline phosphatase (TNAP) chromatin was increased with LRP6 deficiency and reduced with G3BP1 deficiency. G3BP1 activation of NFATc4 mapped to G3BP1 domains supporting interactions with RIG-I (retinoic acid inducible gene I), a stimulus for mitochondrial antiviral signaling (MAVS) that drives cardiovascular calcification in humans when mutated in Singleton-Merten syndrome (SGMRT2). Gain-of-function SGMRT2/RIG-I mutants increased G3BP1 methylation and synergized with osteogenic transcription factors (Runx2 and NFATc4). A chemical antagonist of G3BP, C108 (C108 is 2-hydroxybenzoic acid, 2-[1-(2-hydroxyphenyl)ethylidene]hydrazide CAS 15533-09-2), down-regulated RIG-I-stimulated G3BP1 methylation, Wnt/NFAT signaling, VSM TNAP activity, and calcification. G3BP1 deficiency reduced RIG-I protein levels and VSM osteogenic programs. Like G3BP1 and RIG-I deficiency, MAVS deficiency reduced VSM osteogenic signals, including TNAP activity and Wnt5-dependent nuclear NFATc4 levels. Aortic calcium accumulation is decreased in MAVS-deficient LDLR-/- mice fed arteriosclerotic diets. The G3BP1/RIG-I/MAVS relay is a component of Wnt signaling. Targeting this relay may help mitigate arteriosclerosis.

Arterial Calcification in Diabetes Mellitus: Preclinical Models and Translational Implications.

Diabetes mellitus increasingly afflicts our aging and dysmetabolic population. Type 2 diabetes mellitus and the antecedent metabolic syndrome represent the vast majority of the disease burden-increasingly prevalent in children and older adults. However, type 1 diabetes mellitus is also advancing in preadolescent children. As such, a crushing wave of cardiometabolic disease burden now faces our society. Arteriosclerotic calcification is increased in metabolic syndrome, type 2 diabetes mellitus, and type 1 diabetes mellitus-impairing conduit vessel compliance and function, thereby increasing the risk for dementia, stroke, heart attack, limb ischemia, renal insufficiency, and lower extremity amputation. Preclinical models of these dysmetabolic settings have provided insights into the pathobiology of arterial calcification. Osteochondrogenic morphogens in the BMP-Wnt signaling relay and transcriptional regulatory programs driven by Msx and Runx gene families are entrained to innate immune responses-responses activated by the dysmetabolic state-to direct arterial matrix deposition and mineralization. Recent studies implicate the endothelial-mesenchymal transition in contributing to the phenotypic drift of mineralizing vascular progenitors. In this brief overview, we discuss preclinical disease models that provide mechanistic insights-and point to challenges and opportunities to translate these insights into new therapeutic strategies for our patients afflicted with diabetes mellitus and its arteriosclerotic complications.

Exercise training reverses age-induced diastolic dysfunction and restores coronary microvascular function.

KEY POINTS: In a rat model of ageing that is free of atherosclerosis or hypertension, E/A, a diagnostic measure of diastolic filling, decreases, and isovolumic relaxation time increases, indicating that both active and passive ventricular relaxation are impaired with advancing age. Resting coronary blood flow and coronary functional hyperaemia are reduced with age, and endothelium-dependent vasodilatation declines with age in coronary resistance arterioles. Exercise training reverses age-induced declines in diastolic and coronary microvascular function. Thus, microvascular dysfunction and inadequate coronary perfusion are likely mechanisms of diastolic dysfunction in aged rats. Exercise training, initiated at an advanced age, reverses age-related diastolic and microvascular dysfunction; these data suggest that late-life exercise training can be implemented to improve coronary perfusion and diastolic function in the elderly. ABSTRACT: The risk for diastolic dysfunction increases with advancing age. Regular exercise training ameliorates age-related diastolic dysfunction; however, the underlying mechanisms have not been identified. We investigated whether (1) microvascular dysfunction contributes to the development of age-related diastolic dysfunction, and (2) initiation of late-life exercise training reverses age-related diastolic and microvascular dysfunction. Young and old rats underwent 10 weeks of exercise training or remained as sedentary, cage-controls. Isovolumic relaxation time (IVRT), early diastolic filling (E/A), myocardial performance index (MPI) and aortic stiffness (pulse wave velocity; PWV) were evaluated before and after exercise training or cage confinement. Coronary blood flow and vasodilatory responses of coronary arterioles were evaluated in all groups at the end of training. In aged sedentary rats, compared to young sedentary rats, a 42% increase in IVRT, a 64% decrease in E/A, and increased aortic stiffness (PWV: 6.36 ± 0.47 vs.4.89 ± 0.41, OSED vs. YSED, P < 0.05) was accompanied by impaired coronary blood flow at rest and during exercise. Endothelium-dependent vasodilatation was impaired in coronary arterioles from aged rats (maximal relaxation to bradykinin: 56.4 ± 5.1% vs. 75.3 ± 5.2%, OSED vs. YSED, P < 0.05). After exercise training, IVRT, a measure of active ventricular relaxation, did not differ between old and young rats. In old rats, exercise training reversed the reduction in E/A, reduced aortic stiffness, and eliminated impairment of coronary blood flow responses and endothelium-dependent vasodilatation. Thus, age-related diastolic and microvascular dysfunction are reversed by late-life exercise training. The restorative effect of exercise training on coronary microvascular function may result from improved endothelial function.

Effects of spaceflight and ground recovery on mesenteric artery and vein constrictor properties in mice.

Following exposure to microgravity, there is a reduced ability of astronauts to augment peripheral vascular resistance, often resulting in orthostatic hypotension. The purpose of this study was to test the hypothesis that mesenteric arteries and veins will exhibit diminished vasoconstrictor responses after spaceflight. Mesenteric arteries and veins from female mice flown on the Space Transportation System (STS)-131 (n=11), STS-133 (n=6), and STS-135 (n=3) shuttle missions and respective ground-based control mice (n=30) were isolated for in vitro experimentation. Vasoconstrictor responses were evoked in arteries via norepinephrine (NE), potassium chloride (KCl), and caffeine, and in veins through NE across a range of intraluminal pressures (2-12 cmH(2)O). Vasoconstriction to NE was also determined in mesenteric arteries at 1, 5, and 7 d postlanding. In arteries, maximal constriction to NE, KCl, and caffeine were reduced immediately following spaceflight and 1 d postflight. Spaceflight also reduced arterial ryanodine receptor-3 mRNA levels. In mesenteric veins, there was diminished constriction to NE after flight. The results indicate that the impaired vasoconstriction following spaceflight occurs through the ryanodine receptor-mediated intracellular Ca(2+) release mechanism. Such vascular changes in astronauts could compromise the maintenance of arterial pressure during orthostatic stress.

Spaceflight-induced alterations in cerebral artery vasoconstrictor, mechanical, and structural properties: implications for elevated cerebral perfusion and intracranial pressure.

Evidence indicates that cerebral blood flow is both increased and diminished in astronauts on return to Earth. Data from ground-based animal models simulating the effects of microgravity have shown that decrements in cerebral perfusion are associated with enhanced vasoconstriction and structural remodeling of cerebral arteries. Based on these results, the purpose of this study was to test the hypothesis that 13 d of spaceflight [Space Transportation System (STS)-135 shuttle mission] enhances myogenic vasoconstriction, increases medial wall thickness, and elicits no change in the mechanical properties of mouse cerebral arteries. Basilar and posterior communicating arteries (PCAs) were isolated from 9-wk-old female C57BL/6 mice for in vitro vascular and mechanical testing. Contrary to that hypothesized, myogenic vasoconstrictor responses were lower and vascular distensibility greater in arteries from spaceflight group (SF) mice (n=7) relative to ground-based control group (GC) mice (n=12). Basilar artery maximal diameter was greater in SF mice (SF: 236±9 µm and GC: 215±5 µm) with no difference in medial wall thickness (SF: 12.4±1.6 µm; GC: 12.2±1.2 µm). Stiffness of the PCA, as characterized via nanoindentation, was lower in SF mice (SF: 3.4±0.3 N/m; GC: 5.4±0.8 N/m). Collectively, spaceflight-induced reductions in myogenic vasoconstriction and stiffness and increases in maximal diameter of cerebral arteries signify that elevations in brain blood flow may occur during spaceflight. Such changes in cerebral vascular control of perfusion could contribute to increases in intracranial pressure and an associated impairment of visual acuity in astronauts during spaceflight.

Mechanical ventilation reduces rat diaphragm blood flow and impairs oxygen delivery and uptake.

OBJECTIVES: Although mechanical ventilation is a life-saving intervention in patients suffering from respiratory failure, prolonged mechanical ventilation is often associated with numerous complications including problematic weaning. In contracting skeletal muscle, inadequate oxygen supply can limit oxidative phosphorylation resulting in muscular fatigue. However, whether prolonged mechanical ventilation results in decreased diaphragmatic blood flow and induces an oxygen supply-demand imbalance in the diaphragm remains unknown. DESIGN: We tested the hypothesis that prolonged controlled mechanical ventilation results in a time-dependent reduction in rat diaphragmatic blood flow and microvascular PO2 and that prolonged mechanical ventilation would diminish the diaphragm's ability to increase blood flow in response to muscular contractions. MEASUREMENTS AND MAIN RESULTS: Compared to 30 mins of mechanical ventilation, 6 hrs of mechanical ventilation resulted in a 75% reduction in diaphragm blood flow (via radiolabeled microspheres), which did not occur in the intercostal muscle or high-oxidative hindlimb muscle (e.g., soleus). There was also a time-dependent decline in diaphragm microvascular PO2 (via phosphorescence quenching). Further, contrary to 30 mins of mechanical ventilation, 6 hrs of mechanical ventilation significantly compromised the diaphragm's ability to increase blood flow during electrically-induced contractions, which resulted in a ~80% reduction in diaphragm oxygen uptake. In contrast, 6 hrs of spontaneous breathing in anesthetized animals did not alter diaphragm blood flow or the ability to augment flow during electrically-induced contractions. CONCLUSIONS: These new and important findings reveal that prolonged mechanical ventilation results in a time-dependent decrease in the ability of the diaphragm to augment blood flow to match oxygen demand in response to contractile activity and could be a key contributing factor to difficult weaning. Although additional experiments are required to confirm, it is tempting to speculate that this ventilator-induced decline in diaphragmatic oxygenation could promote a hypoxia-induced generation of reactive oxygen species in diaphragm muscle fibers and contribute to ventilator-induced diaphragmatic atrophy and contractile dysfunction.

Aging and exercise training reduce testes microvascular PO2 and alter vasoconstrictor responsiveness in testicular arterioles.

Testicular function and associated testosterone concentration decline with advancing age, and an impaired O2 supply may contribute, in part, to this reduction. We hypothesized that there would be a reduced microvascular Po2 (Po2(m)) in the testes from aged rats, and this reduced Po2(m) would be associated with impaired vasomotor control in isolated resistance arterioles. In addition, given the positive effect of exercise on microvascular Po2 and arteriolar function, we further hypothesized that there would be an enhanced Po2(m) in the testes from aged animals after aerobic exercise training. Testicular Po2(m) was measured in vivo via phosphorescence quenching in young and aged sedentary (SED) and exercise-trained (ET; 15 m/min treadmill walking, 15-degree incline, 5 days/wk for 10 wk) male Fischer-344 rats. Vasoconstriction to α-adrenergic [norepinephrine (NE) and phenylephrine (PE)] and myogenic stimuli in testicular arterioles was assessed in vitro. In the SED animals, testicular Po2(m) was reduced by ∼50% with old age (aged SED 11.8 ± 1.9 vs. young SED 22.1 ± 1.1 mmHg; P = 0.0001). Contrary to our hypothesis, exercise training did not alter Po2(m) in the aged group and reduced testicular Po2(m) in the young animals, abolishing age-related differences (young ET, 10.0 ± 0.8 vs. aged ET, 10.7 ± 0.9 mmHg; P = 0.37). Vasoconstrictor responsiveness to NE and PE was diminished in aged compared with young (NE: young SED, 58 ± 2 vs. aged SED, 47 ± 2%; P = 0.001) (PE: young SED, 51 ± 3 vs. aged SED, 36 ± 5%; P = 0.008). Exercise training did not alter maximal vasoconstriction to NE in young or aged groups. In summary, advancing age is associated with a reduced testis Po2(m) and impaired adrenergic vasoconstriction. The diminished testicular microvascular driving pressure of O2 and associated vascular dysfunction provides mechanistic insight into the old age-related decrease in testicular function, and a reduced Po2(m) may contribute, in part, to reduced fertility markers after exercise training.

Effects of spaceflight on the murine mandible: Possible factors mediating skeletal changes in non-weight bearing bones of the head.

Spaceflight-induced remodeling of the skull is characterized by greater bone volume, mineral density, and mineral content. To further investigate the effects of spaceflight on other non-weight bearing bones of the head, as well as to gain insight into potential factors mediating the remodeling of the skull, the purpose of the present study was to determine the effects of spaceflight on mandibular bone properties. Female C57BL/6 mice were flown 15d on the STS-131 Space Shuttle mission (n=8) and 13d on the STS-135 mission (n=5) or remained as ground controls (GC). Upon landing, mandibles were collected and analyzed via micro-computed tomography for tissue mineralization, bone volume (BV/TV), and distance from the cemento-enamel junction to the alveolar crest (CEJ-AC). Mandibular mineralization was not different between spaceflight (SF) and GC mice for either the STS-131 or STS-135 missions. Mandibular BV/TV (combined cortical and trabecular bone) was lower in mandibles from SF mice on the STS-131 mission (80.7±0.8%) relative to that of GC (n=8) animals (84.2±1.2%), whereas BV/TV from STS-135 mice was not different from GC animals (n=7). The CEJ-AC distance was shorter in mandibles from STS-131 mice (0.217±0.004mm) compared to GC animals (0.283±0.009mm), indicating an anabolic (or anti-catabolic) effect of spaceflight, while CEJ-AC distance was similar between STS-135 and GC mice. These findings demonstrate that mandibular bones undergo skeletal changes during spaceflight and are susceptible to the effects of weightlessness. However, adaptation of the mandible to spaceflight is dissimilar to that of the cranium, at least in terms of changes in BV/TV.

Effects of hindlimb unloading and ionizing radiation on skeletal muscle resistance artery vasodilation and its relation to cancellous bone in mice.

Spaceflight has profound effects on vascular function as a result of weightlessness that may be further compounded by radiation exposure. The purpose of the present study was to assess the individual and combined effects of hindlimb unloading (HU) and radiation (Rad) on vasodilator responses in the skeletal muscle vasculature. Adult male C57BL/6J mice were randomized to one of four groups: control (Con), HU (tail suspension for 15 days), Rad (200 cGy of (137)Cs), and HU-Rad (15-day tail suspension and 200 cGy of (137)Cs). Endothelium-dependent vasodilation of gastrocnemius feed arteries was assessed in vitro using acetylcholine (ACh, 10(-9)-10(-4) M) and inhibitors of nitric oxide synthase (NOS) and cyclooxygenase (COX). Endothelium-independent vasodilation was assessed using Dea-NONOate (10(-9)-10(-4) M). Endothelium-dependent and -independent vasodilator responses were impaired relative to Con responses in all treatment groups; however, there was no further impairment from the combination of treatments (HU-Rad) relative to that in the HU and Rad groups. The NOS-mediated contribution to endothelium-dependent vasodilation was depressed with HU and Rad. This impairment in NOS signaling may have been partially compensated for by an enhancement of PGI2-mediated dilation. Changes in endothelium-dependent vasodilation were also associated with decrements in trabecular bone volume in the proximal tibia metaphysis. These data demonstrate that the simulated space environment (i.e., radiation exposure and unloading of muscle and bone) significantly impairs skeletal muscle artery vasodilation, mediated through endothelium-dependent reductions in NOS signaling and decrements in vascular smooth muscle cell responsiveness to NO.

Blood flow responses to mild-intensity exercise in ectopic vs. orthotopic prostate tumors; dependence upon host tissue hemodynamics and vascular reactivity.

Given the critical role of tumor O2 delivery in patient prognosis and the rise in preclinical exercise oncology studies, we investigated tumor and host tissue blood flow at rest and during exercise as well as vascular reactivity using a rat prostate cancer model grown in two transplantation sites. In male COP/CrCrl rats, blood flow (via radiolabeled microspheres) to prostate tumors [R3327-MatLyLu cells injected in the left flank (ectopic) or ventral prostate (orthotopic)] and host tissue was measured at rest and during a bout of mild-intensity exercise. α-Adrenergic vasoconstriction to norepinephrine (NE: 10(-9) to 10(-4) M) was determined in arterioles perforating the tumors and host tissue. To determine host tissue exercise hyperemia in healthy tissue, a sham-operated group was included. Blood flow was lower at rest and during exercise in ectopic tumors and host tissue (subcutaneous adipose) vs. the orthotopic tumor and host tissue (prostate). During exercise, blood flow to the ectopic tumor significantly decreased by 25 ± 5% (SE), whereas flow to the orthotopic tumor increased by 181 ± 30%. Maximal vasoconstriction to NE was not different between arterioles from either tumor location. However, there was a significantly higher peak vasoconstriction to NE in subcutaneous adipose arterioles (92 ± 7%) vs. prostate arterioles (55 ± 7%). Establishment of the tumor did not alter host tissue blood flow from either location at rest or during exercise. These data demonstrate that blood flow in tumors is dependent on host tissue hemodynamics and that the location of the tumor may critically affect how exercise impacts the tumor microenvironment and treatment outcomes.

Effects of High-LET Radiation Exposure and Hindlimb Unloading on Skeletal Muscle Resistance Artery Vasomotor Properties and Cancellous Bone Microarchitecture in Mice.

Weightlessness during spaceflight leads to functional changes in resistance arteries and loss of cancellous bone, which may be potentiated by radiation exposure. The purpose of this study was to assess the effects of hindlimb unloading (HU) and total-body irradiation (TBI) on the vasomotor responses of skeletal muscle arteries. Male C57BL/6 mice were assigned to control, HU (13-16 days), TBI (1 Gy (56)Fe, 600 MeV, 10 cGy/min) and HU-TBI groups. Gastrocnemius muscle feed arteries were isolated for in vitro study. Endothelium-dependent (acetylcholine) and -independent (Dea-NONOate) vasodilator and vasoconstrictor (KCl, phenylephrine and myogenic) responses were evaluated. Arterial endothelial nitric oxide synthase (eNOS), superoxide dismutase-1 (SOD-1) and xanthine oxidase (XO) protein content and tibial cancellous bone microarchitecture were quantified. Endothelium-dependent and -independent vasodilator responses were impaired in all groups relative to control, and acetylcholine-induced vasodilation was lower in the HU-TBI group relative to that in the HU and TBI groups. Reductions in endothelium-dependent vasodilation correlated with a lower cancellous bone volume fraction. Nitric oxide synthase inhibition abolished all group differences in endothelium-dependent vasodilation. HU and HU-TBI resulted in decreases in eNOS protein levels, while TBI and HU-TBI produced lower SOD-1 and higher XO protein content. Vasoconstrictor responses were not altered. Reductions in NO bioavailability (eNOS), lower anti-oxidant capacity (SOD-1) and higher pro-oxidant capacity (XO) may contribute to the deficits in NOS signaling in skeletal muscle resistance arteries. These findings suggest that the combination of insults experienced in spaceflight leads to impairment of vasodilator function in resistance arteries that is mediated through deficits in NOS signaling.

Type 2 diabetes alters bone and marrow blood flow and vascular control mechanisms in the ZDF rat.

Bone health and cardiovascular function are compromised in individuals with type 2 diabetes mellitus (T2DM). The purpose of this study was to determine whether skeletal vascular control mechanisms are altered during the progression of T2DM in Zucker diabetic fatty (ZDF) rats. Responses of the principal nutrient artery (PNA) of the femur from obese ZDF rats with prediabetes, short-term diabetes, and long-term diabetes to endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) vasodilation and potassium chloride, norepinephrine (NE), and a myogenic vasoconstrictor were determined in vitro. Few changes in the PNA vasomotor responses occurred for the prediabetic and short-term diabetic conditions. Endothelium-dependent and -independent vasodilation were reduced, and NE and myogenic vasoconstriction were increased in obese ZDF rats with long-term diabetes relative to lean age-matched controls. Differences in endothelium-dependent vasodilation of the femoral PNA between ZDF rats and controls were abolished by the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester. The passive pressure-diameter response of the femoral PNA was also lower across a range of intraluminal pressures with long-term T2DM. Regional bone and marrow perfusion and vascular conductance, measured in vivo using radiolabeled microspheres, were lower in obese ZDF rats with long-term diabetes. These findings indicate that the profound impairment of the bone circulation may contribute to the osteopenia found to occur in long bones during chronic T2DM.

Spaceflight on the Bion-M1 biosatellite alters cerebral artery vasomotor and mechanical properties in mice.

Conditions during spaceflight, such as the loss of the head-to-foot gravity vector, are thought to potentially alter cerebral blood flow and vascular resistance. The purpose of the present study was to determine the effects of long-term spaceflight on the functional, mechanical, and structural properties of cerebral arteries. Male C57BL/6N mice were flown 30 days in a Bion-M1 biosatellite. Basilar arteries isolated from spaceflight (SF) (n = 6), habitat control (HC) (n = 6), and vivarium control (VC) (n = 16) mice were used for in vitro functional and mechanical testing and histological structural analysis. The results demonstrate that vasoconstriction elicited through a voltage-gated Ca(2+) mechanism (30-80 mM KCl) and thromboxane A2 receptors (10(-8) - 3 × 10(-5) M U46619) are lower in cerebral arteries from SF mice. Inhibition of Rho-kinase activity (1 µM Y27632) abolished group differences in U46619-evoked contractions. Endothelium-dependent vasodilation elicited by acetylcholine (10 µM, 2 µM U46619 preconstriction) was virtually absent in cerebral arteries from SF mice. The pressure-diameter relation was lower in arteries from SF mice relative to that in HC mice, which was not related to differences in the extracellular matrix protein elastin or collagen content or the elastin/collagen ratio in the basilar arteries. Diameter, medial wall thickness, and medial cross-sectional area of unpressurized basilar arteries were not different among groups. These results suggest that the microgravity-induced attenuation of both vasoconstrictor and vasodilator properties may limit the range of vascular control of cerebral perfusion or impair the distribution of brain blood flow during periods of stress.

Modulation of blood flow, hypoxia, and vascular function in orthotopic prostate tumors during exercise.

BACKGROUND: Previous studies have hypothesized that tumor blood flow may be elevated or reduced during exercise, which could impact the tumor microenvironment. However, to date technical limitations have precluded the measurement of tumor blood flow during exercise. Using an orthotopic preclinical model of prostate cancer, we tested the hypotheses that during exercise tumors would experience 1) diminished vascular resistance, 2) augmented blood flow, 3) increased numbers of perfused vessels, and 4) decreased tissue hypoxia and, furthermore, that the increased perfusion would be associated with diminished vasoconstriction in prostate tumor arterioles. METHODS: Dunning R-3327 MatLyLu tumor cells were injected into the ventral prostate of male Copenhagen rats aged 4 to 6 months randomly assigned to tumor-bearing (n = 42) or vehicle control (n = 14) groups. Prostate tumor blood flow, vascular resistance, patent vessel number, and hypoxia were measured in vivo in conscious rats at rest and during treadmill exercise, and vasoconstrictor responsiveness of resistance arterioles was investigated in vitro. RESULTS: During exercise there was a statistically significant increase in tumor blood flow (approximately 200%) and number of patent vessels (rest mean ± standard deviation [SD] = 12.7±1.3; exercise mean ± SD = 14.3±0.6 vessels/field; Student t test two-sided P = .02) and decreased hypoxia compared with measurements made at rest. In tumor arterioles, the maximal constriction elicited by norepinephrine was blunted by approximately 95% vs control prostate vessels. CONCLUSIONS: During exercise there is enhanced tumor perfusion and diminished tumor hypoxia due, in part, to a diminished vasoconstriction. The clinical relevance of these findings are that exercise may enhance the delivery of tumor-targeting drugs as well as attenuate the hypoxic microenvironment within a tumor and lead to a less aggressive phenotype.

Exercise training augments regional bone and marrow blood flow during exercise.

INTRODUCTION: The principal nutrient artery to the femur demonstrates an increase in nitric oxide-mediated vasodilation in rats after treadmill exercise training. The present study sought to determine whether exercise training improves hindlimb bone and marrow blood flow distribution at rest and during exercise. METHODS: Six 8-month old male Sprague-Dawley rats were exercise trained (ET) with treadmill walking at 15 m · min(-1) up a 15° incline for 60 min · d(-1) over a 10- to 12-wk period. Sedentary (SED) control animals were acclimated to treadmill exercise for 5 min · d(-1) during the week preceding the blood flow measurements. Blood flow to nine distinct regions of the femur, tibia, and fibula was determined at rest and during low-intensity exercise (15 m · min(-1) walking, 0° incline) using the reference sample microsphere method. RESULTS: The results demonstrate an augmentation of exercise hyperemia above that observed in SED rats during exercise in only one region of the bone, the femoral diaphysis, of ET rats. However, whereas exercise hyperemia occurred in three of the nine hindlimb bone regions measured in SED rats, exercise hyperemia occurred in seven of nine regions in ET rats. CONCLUSIONS: These data indicate an increase in generalized hindlimb bone and marrow blood flow during physical activity after a period of exercise training. Elevations in regional bone and marrow blood flow after training may augment medullary pressure and bone interstitial fluid flow, thus benefiting bone integrity.

Chronic skeletal unloading of the rat femur: mechanisms and functional consequences of vascular remodeling.

Chronic skeletal unloading diminishes hindlimb bone blood flow. The purpose of the present investigation was to determine 1) whether 7 and 14days of skeletal unloading alter femoral bone and marrow blood flow and vascular resistance during reloading, and 2) whether putative changes in bone perfusion are associated with a gross structural remodeling of the principal nutrient artery (PNA) of the femur. Six-month old male Sprague-Dawley rats were assigned to 7-d or 14-d hindlimb unloading (HU) or weight-bearing control groups. Bone perfusion was measured following 10min of standing (reloading) following the unloading treatment. Histomorphometry was used to determine PNA media wall thickness and maximal diameter. Bone blood flow, arterial pressure and PNA structural characteristics were used to calculate arterial shear stress and circumferential wall stress. During reloading, femoral perfusion was lower in the distal metaphyseal region of 7-d HU rats, and in the proximal and distal metaphyses, diaphysis and diaphyseal marrow of 14-d HU animals relative to that in control rats. Vascular resistance was also higher in all regions of the femur in 14-d HU rats during reloading relative to control animals. Intraluminal diameter of PNAs from 14-d HU rats (138±5µm) was smaller than that of control PNAs (162±6µm), and medial wall thickness was thinner in PNAs from 14-d HU (14.3±0.6µm) versus that of control (18.0±0.8µm) rats. Decreases in both shear stress and circumferential stress occurred in the PNA with HU that later returned to control levels with the reductions in PNA maximal diameter and wall thickness, respectively. The results demonstrate that chronic skeletal unloading attenuates the ability to increase blood flow and nutrient delivery to bone and marrow with immediate acute reloading due, in part, to a remodeling of the bone resistance vasculature.

Differential effects of aging and exercise on intra-abdominal adipose arteriolar function and blood flow regulation.

Adipose tissue (AT), which typically comprises an increased percentage of body mass with advancing age, receives a large proportion of resting cardiac output. During exercise, an old age-associated inability to increase vascular resistance within the intra-abdominal AT may compromise the ability of the cardiovascular system to redistribute blood flow to the active musculature, contributing to the decline in exercise capacity observed in this population. We tested the hypotheses that 1) there would be an elevated perfusion of AT during exercise with old age that was associated with diminished vasoconstrictor responses of adipose-resistance arteries, and 2) chronic exercise training would mitigate the age-associated alterations in AT blood flow and vascular function. Young (6 mo; n = 40) and old (24 mo; n = 28) male Fischer 344 rats were divided into young sedentary (YSed), old sedentary (OSed), young exercise trained (YET), or old exercise trained (OET) groups, where training consisted of 10-12 wk of treadmill exercise. In vivo blood flow at rest and during exercise and in vitro α-adrenergic and myogenic vasoconstrictor responses in resistance arteries from AT were measured in all groups. In response to exercise, there was a directionally opposite change in AT blood flow in the OSed group (≈ 150% increase) and YSed (≈ 55% decrease) vs. resting values. Both α-adrenergic and myogenic vasoconstriction were diminished in OSed vs. YSed AT-resistance arteries. Exercise training resulted in a similar AT hyperemic response between age groups during exercise (YET, 9.9 ± 0.5 ml · min(-1) · 100(-1) g; OET, 8.1 ± 0.9 ml · min(-1) · 100(-1) g) and was associated with enhanced myogenic and α-adrenergic vasoconstriction of AT-resistance arteries from the OET group relative to OSed. These results indicate that there is an inability to increase vascular resistance in AT during exercise with old age, due, in part, to a diminished vasoconstriction of AT arteries. Furthermore, the results indicate that exercise training can augment vasoconstriction of AT arteries and mitigate age-related alterations in the regulation of AT blood flow during exercise.

Effects of aging and exercise training on skeletal muscle blood flow and resistance artery morphology.

With old age, blood flow to the high-oxidative red skeletal muscle is reduced and blood flow to the low-oxidative white muscle is elevated during exercise. Changes in the number of feed arteries perforating the muscle are thought to contribute to this altered hyperemic response during exercise. We tested the hypothesis that exercise training would ameliorate age-related differences in blood flow during exercise and feed artery structure in skeletal muscle. Young (6-7 mo old, n = 36) and old (24 mo old, n = 25) male Fischer 344 rats were divided into young sedentary (Sed), old Sed, young exercise-trained (ET), and old ET groups, where training consisted of 10-12 wk of treadmill exercise. In Sed and ET rats, blood flow to the red and white portions of the gastrocnemius muscle (Gast(Red) and Gast(White)) and the number and luminal cross-sectional area (CSA) of all feed arteries perforating the muscle were measured at rest and during exercise. In the old ET group, blood flow was greater to Gast(Red) (264 ± 13 and 195 ± 9 ml · min(-1) · 100 g(-1) in old ET and old Sed, respectively) and lower to Gast(White) (78 ± 5 and 120 ± 6 ml · min(-1) · 100 g(-1) in old ET and old Sed, respectively) than in the old Sed group. There was no difference in the number of feed arteries between the old ET and old Sed group, although the CSA of feed arteries from old ET rats was larger. In young ET rats, there was an increase in the number of feed arteries perforating the muscle. Exercise training mitigated old age-associated differences in blood flow during exercise within gastrocnemius muscle. However, training-induced adaptations in resistance artery morphology differed between young (increase in feed artery number) and old (increase in artery CSA) animals. The altered blood flow pattern induced by exercise training with old age would improve the local matching of O(2) delivery to consumption within the skeletal muscle.

Spaceflight reduces vasoconstrictor responsiveness of skeletal muscle resistance arteries in mice.

Cardiovascular adaptations to microgravity undermine the physiological capacity to respond to orthostatic challenges upon return to terrestrial gravity. The purpose of the present study was to investigate the influence of spaceflight on vasoconstrictor and myogenic contractile properties of mouse gastrocnemius muscle resistance arteries. We hypothesized that vasoconstrictor responses acting through adrenergic receptors [norepinephrine (NE)], voltage-gated Ca(2+) channels (KCl), and stretch-activated (myogenic) mechanisms would be diminished following spaceflight. Feed arteries were isolated from gastrocnemius muscles, cannulated on glass micropipettes, and physiologically pressurized for in vitro experimentation. Vasoconstrictor responses to intraluminal pressure changes (0-140 cmH(2)O), KCl (10-100 mM), and NE (10(-9)-10(-4) M) were measured in spaceflown (SF; n = 11) and ground control (GC; n = 11) female C57BL/6 mice. Spaceflight reduced vasoconstrictor responses to KCl and NE; myogenic vasoconstriction was unaffected. The diminished vasoconstrictor responses were associated with lower ryanodine receptor-2 (RyR-2) and ryanodine receptor-3 (RyR-3) mRNA expression, with no difference in sarcoplasmic/endoplasmic Ca(2+) ATPase 2 mRNA expression. Vessel wall thickness and maximal intraluminal diameter were unaffected by spaceflight. The data indicate a deficit in intracellular calcium release via RyR-2 and RyR-3 in smooth muscle cells as the mechanism of reduced contractile activity in skeletal muscle after spaceflight. Furthermore, the results suggest that impaired end-organ vasoconstrictor responsiveness of skeletal muscle resistance arteries contributes to lower peripheral vascular resistance and less tolerance of orthostatic stress in humans after spaceflight.

Effects of aging and exercise training on spinotrapezius muscle microvascular PO2 dynamics and vasomotor control.

With advancing age, there is a reduction in exercise tolerance, resulting, in part, from a perturbed ability to match O(2) delivery to uptake within skeletal muscle. In the spinotrapezius muscle (which is not recruited during incline treadmill running) of aged rats, we tested the hypotheses that exercise training will 1) improve the matching of O(2) delivery to O(2) uptake, evidenced through improved microvascular Po(2) (Pm(O(2))), at rest and throughout the contractions transient; and 2) enhance endothelium-dependent vasodilation in first-order arterioles. Young (Y, ∼6 mo) and aged (O, >24 mo) Fischer 344 rats were assigned to control sedentary (YSED; n = 16, and OSED; n = 15) or exercise-trained (YET; n = 14, and OET; n = 13) groups. Spinotrapezius blood flow (via radiolabeled microspheres) was measured at rest and during exercise. Phosphorescence quenching was used to quantify Pm(O(2)) in vivo at rest and across the rest-to-twitch contraction (1 Hz, 5 min) transition in the spinotrapezius muscle. In a follow-up study, vasomotor responses to endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) stimuli were investigated in vitro. Blood flow to the spinotrapezius did not increase above resting values during exercise in either young or aged groups. Exercise training increased the precontraction baseline Pm(O(2)) (OET 37.5 ± 3.9 vs. OSED 24.7 ± 3.6 Torr, P < 0.05); the end-contracting Pm(O(2)) and the time-delay before Pm(O(2)) fell in the aged group but did not affect these values in the young. Exercise training improved maximal vasodilation in aged rats to acetylcholine (OET 62 ± 16 vs. OSED 27 ± 16%) and to sodium nitroprusside in both young and aged rats. Endurance training of aged rats enhances the Pm(O(2)) in a nonrecruited skeletal muscle and is associated with improved vascular smooth muscle function. These data support the notion that improvements in vascular function with exercise training are not isolated to the recruited muscle.