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

Area of Science:

• Physiology
• Sports Science
• Nutrition Science

Background:

• Plasma nitrite ([NO2-]) is a key mediator of vasodilation and blood pressure regulation.
• Nitrate ([NO3-]) supplementation, often from beetroot juice, is known to increase plasma nitrite levels.
• Understanding how physiological changes affect these markers is crucial for accurate interpretation of research.

Purpose of the Study:

• To investigate the impact of postural changes on plasma volume (PV), nitrate ([NO3-]), and nitrite ([NO2-]) concentrations.
• To determine if elevated plasma [NO3-] and [NO2-] influence these postural effects.

Main Methods:

• Fourteen healthy participants underwent two trials: one with nitrate-rich beetroot juice (BR) and one control (CON).
• Participants maintained a supine position for 30 minutes, followed by 2 minutes of standing, 2 minutes of sitting, and 5 minutes of cycling.
• Plasma [NO3-] and [NO2-] were measured using gas-phase chemiluminescence, and changes in PV were calculated.

Main Results:

• Plasma nitrite ([NO2-]) decreased after lying supine but increased during standing and sitting in both BR and CON trials.
• Plasma nitrite remained elevated post-exercise only in the CON trial.
• Plasma nitrate ([NO3-]) levels did not differ significantly across measurement points.
• Plasma volume (PV) increased when supine and decreased upon standing, sitting, and during exercise in both trials.

Conclusions:

• Postural changes induce rapid and consistent alterations in plasma nitrite concentrations.
• The influence of posture on plasma nitrite must be considered during experimental measurements.
• Elevated nitrate intake did not alter the postural effects on plasma nitrite but did result in higher baseline levels.