Changes in body posture alter plasma nitrite but not nitrate concentration in humans

• Published in: Nitric oxide Vol. 72; pp. 59 - 65
• Main Authors: Liddle, Luke, Monaghan, Christopher, Burleigh, Mia C., McIlvenna, Luke C., Muggeridge, David J., Easton, Chris
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 30.01.2018
• Subjects: Adult; Beetroot juice; Blood Pressure; Dietary Supplements; Exercise; Female; Fruit and Vegetable Juices; Heart Rate; Humans; Male; Nitrates - administration & dosage; Nitrates - blood; Nitrites - blood; Plasma Volume; Posture - physiology; Beetroot juice; Plasma volume; Exercise
• ISSN: 1089-8603; 1089-8611
• DOI: 10.1016/j.niox.2017.11.008

This study evaluated the change (Δ) in plasma volume (PV), nitrate [NO3−], and nitrite [NO2−] concentration following changes in posture in the presence and absence of elevated plasma [NO3−] and [NO2−] Fourteen healthy participants completed two trials that were preceded by either supplementation with NO3−-rich beetroot juice (BR; total of ∼31 mmol NO3−) or no supplementation (CON). Both trials comprised 30 min of lying supine followed by 2 min of standing, 2 min of sitting and 5 min of sub-maximal cycling. Measurements of plasma [NO3−] and [NO2−] were made by gas-phase chemiluminescence and ΔPV was estimated using the Dill and Costill method. Plasma [NO2−] decreased from baseline (CON: 120 ± 49 nM, BR: 357 ± 129 nM) after lying supine for 30 min (CON 77 ± 30 nM; BR 231 ± 92 nM, both P < 0.01) before increasing during standing (CON 109 ± 42 nM; BR 297 ± 105 nM, both P < 0.01) and sitting (CON 131 ± 43 nM; BR 385 ± 125 nM, both P < 0.01). Plasma [NO2−] remained elevated following exercise only in CON (125 ± 61 nM P = 0.02). Plasma [NO3−] was not different between measurement points in either condition (P > 0.05). PV increased from baseline during the supine phase before decreasing upon standing, sitting, and exercise in both trials (all P<0.05). Changing body posture causes rapid and consistent alterations in plasma [NO2−]. Researchers should therefore carefully consider the effect of posture when measuring this variable. •Plasma nitrite concentration is altered substantially by changes in body posture.•Postural changes in nitrite are consistent regardless of the baseline concentration.•Postural changes in plasma volume do not fully account for the change in nitrite.•Plasma nitrate concentration is not affected by body posture.