Dietary nitrate improves muscle microvascular reactivity and lowers blood pressure at rest and during isometric exercise in untreated hypertensives

Abstract

Objective: This double-blind, cross-over study examined in drug-naïve hypertensives the effects of a single dose of dietary nitrate (beetroot juice, BRJ) on (a) office/ambulatory BP and arterial stiffness, (b) muscle microvascular function, and (c) hemodynamic responses and cardiovagal baroreceptor sensitivity (cBRS) at rest and during isometric exercise.

Methods: Eighteen untreated hypertensives (44.0 ± 2.6 years) consumed randomly, a nitrate-rich (8.1 mmol-BRJ_nitrate ) and a nitrate-depleted (BRJ_placebo ) BRJ. Office BP and pulse wave velocity were assessed before/after BRJ. An occlusion-reperfusion maneuver with continuous monitoring of muscle oxygenated hemoglobin (O₂ Hb) and total hemoglobin (tHb), via NIRS, followed. Participants performed submaximal isometric handgrip with beat-by-beat monitoring of hemodynamics and cBRS. Ambulatory BP assessment followed.

Results: During reperfusion, following arterial occlusion, the magnitude and rate of muscle microvascular reoxygenation (O₂ Hb) and red blood cell content (tHb) were higher in BRJ_nitrate vs BRJ_placebo (P < 0.05), suggesting improved microvascular reactivity. Office/ambulatory BP were lower following BRJ_nitrate vs BRJ_placebo (P < 0.05); pulse-wave-velocity was not altered. During isometric handgrip, BP and peripheral resistance rise were smaller in BRJ_nitrate vs BRJ_placebo (P < 0.01-0.05), with no differences in cBRS.

Conclusions: In drug-naïve hypertensives, a single dose of BRJ induces (a) short-term reductions in resting/ambulatory BP, (b) acute improvements in muscle microvascular function, and (c) attenuation in BP and peripheral resistance responses during isometric exercise.

Keywords: baroreceptor sensitivity; beetroot; blood pressure; dietary nitrate; exercise; hypertension; isometric; microcirculation; microvascular; pulse wave velocity.