Impact of dietary nitrate supplementation via beetroot juice on exercising muscle vascular control in rats

Abstract

Key points• Inorganic nitrate (NO 3 − ) supplementation with beetroot juice (BR) in humans lowers blood pressure and the O 2 cost of exercise and may improve exercise tolerance following its reduction to nitrite (NO 2 − ) and nitric oxide (NO).• The effect of inorganic NO 3 − supplementation with BR on skeletal muscle blood flow (BF) and vascular conductance (VC) within and among locomotory muscles during exercise is unknown.• Inorganic NO 3 − 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 NO 3 − supplementation improves vascular control and elevates skeletal muscle O 2 delivery during exercise predominantly in fast-twitch type II muscles, and provide a potential mechanism by which NO 3 − supplementation improves metabolic control. Abstract Dietary nitrate (NO 3− ) supplementation, via its reduction to nitrite (NO 2 − ) and subsequent conversion to nitric oxide (NO) and other reactive nitrogen intermediates, reduces blood pressure and the O 2 cost of submaximal exercise in humans. Despite these observations, the effects of dietary NO 3 − supplementation on skeletal muscle vascular control during locomotory exercise remain unknown. We tested the hypotheses that dietary NO 3 − 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 NO 3 − (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 NO 3 − supplementation improves vascular control and elevates skeletal muscle O 2 delivery during exercise predominantly in fast-twitch type II muscles, and provide a potential mechanism by which NO 3 − supplementation improves metabolic control.

Acute whole body UVA irradiation combined with nitrate ingestion enhances time trial performance in trained cyclists

“…Hernandez et al, (2012) demonstrated that supplementation with beetroot juice increased force production of the fast twitch muscle fibers of mice which was also associated with an alteration in muscle protein expression. Again using a murine model, Ferguson et al, (2013) also reported that the increase in muscle blood flow following supplementation with beetroot juice only occurred in type II muscle fibers. It is conceivable, therefore, that the blunted response to nitrate supplementation may be attributable to the training status or indeed the muscle fiber type distribution of the participants.…”

“…Evidence from murine models also suggests that increases in muscle blood flow and contractile force production following nitrate supplementation only occur in Type II muscle fibers (Ferguson et al, 2013, Hernandez et al, 2012. One may, therefore, reasonably assume that elite endurance athletes, who are known to have high proportions of type I muscle fibers, would be less likely to benefit from nitrate supplementation (Andersen et al, 2000).…”

Dietary nitrate supplementation enhances high-intensity running performance in moderate normobaric hypoxia, independent of aerobic fitness

“…Nitrate supplementation had no effect on severe-intensity cycling TTE in normoxia, but improved TTE by ~ 8.6 % in hypoxia relative to placebo. Further, there is evidence from murine model investigations that nitrate supplementation may enhance tissue blood flow [41,42] and muscle contractile function [9] preferentially in type II muscle fibres. It is therefore possible that nitrate supplementation is more effective during shorter more high-intensity exercise, during which these muscle fibres are more heavily recruited [9,[43][44][45]64], or else in individuals with greater distribution of type II muscle fibres [43].…”

“…Evidence from murine models suggests that the effects of dietary nitrate supplementation may be fibre type specific, increasing muscle perfusion and oxygenation [41,42], and enhancing calcium handling and force production [9] in type II muscle fibres only, as may be recruited during high-intensity exercise (for review, see Jones et al [43]). Moreover, nitrate supplementation has been demonstrated to elicit beneficial effects when the contribution of type II muscle towards force generation is high, including at fast but not slow muscle contraction frequencies [44], and during the transition from moderate to severe but not unloaded to moderate intensity exercise [45].…”

The effects of dietary nitrate supplementation on the adaptations to sprint interval training in previously untrained males

“…In addition, recent studies in mice have also shown that it can increase 251 muscle force production 21 and increase blood flow to type II muscle fibers 22 . The precise 252 pathway underpinning this ergogenic effect is unclear but the reduction in exercise-induced…”