Key points: Inorganic nitrate (NO₃⁻) supplementation with beetroot juice (BR) in humans lowers blood pressure and the O₂ cost of exercise and may improve exercise tolerance following its reduction to nitrite (NO₂⁻) and nitric oxide (NO). The effect of inorganic NO₃⁻ supplementation with BR on skeletal muscle blood flow (BF) and vascular conductance (VC) within and among locomotory muscles during exercise is unknown. Inorganic NO₃⁻ supplementation with BR in rats resulted in lower exercising mean arterial pressure, lower blood [lactate], and higher total skeletal muscle hindlimb BF and VC during submaximal treadmill running. The greater BF and VC was found in muscles and muscle parts containing primarily type IIb + d/x muscle fibres. These data demonstrate that inorganic NO₃⁻ supplementation improves vascular control and elevates skeletal muscle O₂ delivery during exercise predominantly in fast‐twitch type II muscles, and provide a potential mechanism by which NO₃⁻ supplementation improves metabolic control. Abstract  Dietary nitrate (NO₃⁻) supplementation, via its reduction to nitrite (NO₂⁻) and subsequent conversion to nitric oxide (NO) and other reactive nitrogen intermediates, reduces blood pressure and the O₂ cost of submaximal exercise in humans. Despite these observations, the effects of dietary NO₃⁻ supplementation on skeletal muscle vascular control during locomotory exercise remain unknown. We tested the hypotheses that dietary NO₃⁻ supplementation via beetroot juice (BR) would reduce mean arterial pressure (MAP) and increase hindlimb muscle blood flow in the exercising rat. Male Sprague–Dawley rats (3–6 months) were administered either NO₃⁻ (via beetroot juice; 1 mmol kg⁻¹ day⁻¹, BR n= 8) or untreated (control, n= 11) tap water for 5 days. MAP and hindlimb skeletal muscle blood flow and vascular conductance (radiolabelled microsphere infusions) were measured during submaximal treadmill running (20 m min⁻¹, 5% grade). BR resulted in significantly lower exercising MAP (control: 137 ± 3, BR: 127 ± 4 mmHg, P < 0.05) and blood [lactate] (control: 2.6 ± 0.3, BR: 1.9 ± 0.2 mm, P < 0.05) compared to control. Total exercising hindlimb skeletal muscle blood flow (control: 108 ± 8, BR: 150 ± 11 ml min⁻¹ (100 g)⁻¹, P < 0.05) and vascular conductance (control: 0.78 ± 0.05, BR: 1.16 ± 0.10 ml min⁻¹ (100 g)⁻¹ mmHg⁻¹, P < 0.05) were greater in rats that received BR compared to control. The relative differences in blood flow and vascular conductance for the 28 individual hindlimb muscles and muscle parts correlated positively with their percentage type IIb + d/x muscle fibres (blood flow: r= 0.74, vascular conductance: r= 0.71, P < 0.01 for both). These data support the hypothesis that NO₃⁻ supplementation improves vascular control and elevates skeletal muscle O₂ delivery during exercise predominantly in fast‐twitch type II muscles, and provide a potential mechanism by which NO₃⁻ supplementation improves metabolic control.

Peripheral arterial disease (PAD) results in a failure to adequately supply blood and oxygen (O₂) to working tissues and presents as claudication pain during walking. Nitric oxide (NO) bioavailability is essential for vascular health and function. Plasma nitrite (NO₂⁻) is a marker of vascular NO production but may also be a protected circulating “source” that can be converted to NO during hypoxic conditions, possibly aiding perfusion. We hypothesized that dietary supplementation of inorganic nitrate in the form of beetroot (BR) juice would increase plasma NO₂⁻concentration, increase exercise tolerance, and decrease gastrocnemius fractional O₂extraction, compared with placebo (PL). This was a randomized, open-label, crossover study. At each visit, subjects ( n = 8) underwent resting blood draws, followed by consumption of 500 ml BR or PL and subsequent blood draws prior to, during, and following a maximal cardiopulmonary exercise (CPX) test. Gastrocnemius oxygenation during the CPX was measured by near-infrared spectroscopy. There were no changes from rest for [NO₂⁻] (152 ± 72 nM) following PL. BR increased plasma [NO₂⁻] after 3 h (943 ± 826 nM; P ≤ 0.01). Subjects walked 18% longer before the onset of claudication pain (183 ± 84 s vs. 215 ± 99 s; P ≤ 0.01) and had a 17% longer peak walking time (467 ± 223 s vs. 533 ± 233 s; P ≤ 0.05) following BR vs. PL. Gastrocnemius tissue fractional O₂extraction was lower during exercise following BR (7.3 ± 6.2 vs. 10.4 ± 6.1 arbitrary units; P ≤ 0.01). Diastolic blood pressure was lower in the BR group at rest and during CPX testing ( P ≤ 0.05). These findings support the hypothesis that NO₂⁻-related NO signaling increases peripheral tissue oxygenation in areas of hypoxia and increases exercise tolerance in PAD.

Aerobic exercise training (AET) is an effective adjunct therapy to attenuate the adverse side-effects of adjuvant chemotherapy in women with early breast cancer. Whether AET interacts with the antitumor efficacy of chemotherapy has received scant attention. We carried out a pilot study to explore the effects of AET in combination with neoadjuvant doxorubicin–cyclophosphamide (AC+AET), relative to AC alone, on: (i) host physiology [exercise capacity (VO_2 peak), brachial artery flow-mediated dilation (BA-FMD)], (ii) host-related circulating factors [circulating endothelial progenitor cells (CEP) cytokines and angiogenic factors (CAF)], and (iii) tumor phenotype [tumor blood flow (¹⁵O–water PET), tissue markers (hypoxia and proliferation), and gene expression] in 20 women with operable breast cancer. AET consisted of three supervised cycle ergometry sessions/week at 60% to 100% of VO_2 peak, 30 to 45 min/session, for 12 weeks. There was significant time × group interactions for VO_2 peak and BA-FMD, favoring the AC+AET group (P < 0.001 and P = 0.07, respectively). These changes were accompanied by significant time × group interactions in CEPs and select CAFs [placenta growth factor, interleukin (IL)-1β, and IL-2], also favoring the AC+AET group (P < 0.05). ¹⁵O–water positron emission tomography (PET) imaging revealed a 38% decrease in tumor blood flow in the AC+AET group. There were no differences in any tumor tissue markers (P > 0.05). Whole-genome microarray tumor analysis revealed significant differential modulation of 57 pathways (P < 0.01), including many that converge on NF-κB. Data from this exploratory study provide initial evidence that AET can modulate several host- and tumor-related pathways during standard chemotherapy. The biologic and clinical implications remain to be determined. Cancer Prev Res; 6(9); 925–37. ©2013 AACR.

The aim of this study was to determine if skeletal muscle capillary density is lower in patients with peripheral artery disease (PAD) and if capillary density relates to functional limitations. PAD patients with intermittent claudication (IC) have a decreased exercise tolerance due to exercise-induced muscle ischemia. Despite the apparent role diminished arterial flow has in this population, the degree of walking pain and functional limitation is not entirely explained by altered hemodynamics of the affected limbs. We hypothesized that skeletal muscle capillary density is lower in PAD and is related to the functional impairment observed in this population. Sixty-four patients with PAD and 56 controls underwent cardiopulmonary exercise testing and a gastrocnemius muscle biopsy. A subset of these patients (48 PAD and 47 controls) underwent peak hyperemic flow testing via plethysmography. Capillary density in PAD patients was lower compared with controls ( P < 0.001). After adjustment for several baseline demographic imbalances the model relating capillary density to peak oxygen consumption (V̇o₂) remained significant ( P < 0.001). In PAD subjects, capillary density correlated with peak V̇o₂, peak walking time (PWT), and claudication onset time (COT). Peak hyperemic blood flow related to peak V̇o₂ in both PAD and control subjects. PAD is associated with lower capillary density, and capillary density is related to the functional impairment as defined by a reduced peak V̇o₂, PWT, and COT. These findings suggest that alterations in microcirculation may contribute to functional impairment capacity in PAD.