Premium
Augmented reflex cutaneous vasodilatation following short‐term dietary nitrate supplementation in humans
Author(s) -
Levitt Erica L.,
Keen Jeremy T.,
Wong Brett J.
Publication year - 2015
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/ep085061
Subject(s) - vasodilation , microdialysis , blood pressure , blood flow , nitrate , reflex , sodium nitroprusside , chemistry , laser doppler velocimetry , nitric oxide , mean arterial pressure , hemodynamics , dietary nitrate , medicine , anesthesia , endocrinology , heart rate , nitrite , central nervous system , organic chemistry
New FindingsWhat is the central question of this study? Nitrate supplementation via beetroot juice has been shown to have several benefits in healthy humans, including reduced blood pressure and increased blood flow to exercising muscle. Whether nitrate supplementation can improve blood flow to the skin in heat‐stressed humans has not been investigated.What is the main finding and its importance? Similar to previous studies, we found that nitrate supplementation reduces blood pressure. Nitrate supplementation increased vasodilatation in the skin of heat‐stressed humans but did not directly increase skin blood flow.Nitrate supplementation has been shown to increase NO‐dependent vasodilatation through both NO synthase (NOS)‐dependent and NOS‐independent pathways. We hypothesized that nitrate supplementation would augment reflex cutaneous active vasodilatation. Subjects were equipped with two microdialysis fibres on the forearm randomly assigned as control (Ringer solution) or NOS inhibition (20 m m l ‐NAME). Whole‐body heating was performed to raise core temperature by 0.8°C above baseline core temperature. Maximal cutaneous vasodilatation was achieved via 54 m m sodium nitroprusside and local heating to 43°C. Skin blood flow (measured by laser‐Doppler flowmetry) and blood pressure were measured. Cutaneous vascular conductance (CVC) was calculated as skin blood flow divided by mean arterial pressure (MAP) and expressed as a percentage of maximal CVC (%CVC max ). Subjects underwent heat stress before and after nitrate supplementation (3 days of beetroot juice; 5 m m , 0.45 g nitrates per day). During heat stress, MAP was reduced following nitrate supplementation compared with the control conditions (before 88 ± 3 mmHg versus after 78 ± 2 mmHg; P < 0.05); however, resting MAP was not different between conditions (before 88 ± 3 mmHg versus after 83 ± 2 mmHg; P = 0.117). Nitrate supplementation increased plateau CVC at control sites (before 67 ± 2%CVC max versus after 80 ± 5%CVC max ; P = 0.01) but not at l ‐NAME‐treated sites (before 45 ± 4%CVC max versus after 40 ± 5%CVC max ; P = 0.617). There was no change in the calculated percentage of NOS‐dependent vasodilatation before and after supplementation (before 59 ± 4% versus after 64 ± 6%; P = 0.577). These data suggest that nitrate supplementation augments CVC and reduces MAP during heat stress.