Time course of human skeletal muscle nitrate and nitrite concentration changes following dietary nitrate ingestion

Dietary nitrate (NO₃^-) ingestion can be beneficial for health and exercise performance. Recently, based on animal and limited human studies, a skeletal muscle NO₃^- reservoir has been suggested to be important in whole body nitric oxide (NO) homeostasis. The purpose of this study was to determine the time course of changes in human skeletal muscle NO₃^- concentration ([NO₃^-]) following the ingestion of dietary NO₃^-. Sixteen participants were allocated to either an experimental group (NIT: n = 11) which consumed a bolus of ∼1300 mg (12.8 mmol) potassium nitrate (KNO₃), or a placebo group (PLA: n = 5) which consumed a bolus of potassium chloride (KCl). Biological samples (muscle (vastus lateralis), blood, saliva and urine) were collected shortly before NIT or PLA ingestion and at intervals over the course of the subsequent 24 h. At baseline, no differences were observed for muscle [NO₃^-] and [NO₂^-] between NIT and PLA (P > 0.05). In PLA, there were no changes in muscle [NO₃^-] or [NO₂^-] over time. In NIT, muscle [NO₃^-] was significantly elevated above baseline (54 ± 29 nmol/g) at 0.5 h, reached a peak at 3 h (181 ± 128 nmol/g), and was not different to baseline from 9 h onwards (P > 0.05). Muscle [NO₂^-] did not change significantly over time. Following ingestion of a bolus of dietary NO₃^-, skeletal muscle [NO₃^-] increases rapidly, reaches a peak at ∼3 h and subsequently declines towards baseline values. Following dietary NO₃^- ingestion, human m. vastus lateralis [NO₃^-] expressed a slightly delayed pharmacokinetic profile compared to plasma [NO₃^-].