Inorganic nitrate supplementation attenuates conduit artery retrograde and oscillatory shear in older adults

• Published in: American journal of physiology. Heart and circulatory physiology 2021-03, Vol.320 (3), p.H991-H998
• Main Authors: Casey, Darren P, Bock, Joshua M
• Format: Article
• Language: English
• Subjects: Adults; Age Factors; Aged; Aging; Beta vulgaris; Bioavailability; Blood flow; Blood Flow Velocity; Blood pressure; Brachial Artery - diagnostic imaging; Brachial Artery - drug effects; Brachial Artery - physiology; Conductance; Cross-Over Studies; Crossovers; Diameters; Dietary Supplements; Doppler effect; Double-Blind Method; Female; Forearm; Forearm - blood supply; Fruit and Vegetable Juices; Hemodynamics - drug effects; Humans; Hyperemia; Male; Middle Aged; Nitrates; Nitrates - administration & dosage; Nitrates - blood; Nitric oxide; Older people; Placebos; Regional Blood Flow; Shear rate; Supplements; Time Factors; Treatment Outcome; Ultrasound; Veins & arteries
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.00843.2020

Aging causes deleterious changes in resting conduit artery shear patterns and reduced blood flow during exercise partially attributable to reduced nitric oxide (NO). Inorganic nitrate increases circulating NO bioavailability and may, therefore, improve age-associated changes in shear rate as well as exercise hyperemia. Ten older adults (age: 67 ± 3 yr) consumed 4.03 mmol nitrate and 0.29 mmol nitrite (active) or devoid of both (placebo) daily for 4 wk in a randomized, double-blinded, crossover fashion. Brachial artery diameter (D) and blood velocity (V ) were measured via Doppler ultrasound at rest for the characterization of shear profile as well as during two handgrip exercise trials (4 and 8 kg) for calculation of forearm blood flow (V × cross-sectional area, FBF) and conductance [FBF/mean arterial pressure, forearm vascular conductance (FVC)]. Plasma [nitrate] and [nitrite] increased following active ( < 0.05 for both) but not placebo ( = 0.68 and 0.40, respectively) supplementation. Neither mean nor antegrade shear rate changed following either supplement (beverage-by-time = 0.14 and 0.21, respectively). Retrograde (-13.4 ± 7.0 to -9.7 ± 6.8·s ) and oscillatory (0.20 ± 0.08 to 0.15 ± 0.09 A.U., < 0.05 for both) shear decreased following active, but not placebo ( = 0.81 and 0.70, respectively), supplementation. The FBF response (Δ from rest) to neither 4-kg nor 8-kg trials changed following either supplement (beverage-by-time = 0.53 and 0.11, respectively). Similarly, no changes were observed in FVC responses to 4-kg or 8-kg trials (beverage-by-time = 0.23 and 0.07, respectively). These data indicate that inorganic nitrate supplementation improves conduit artery shear profiles, but not exercise hyperemia, in older adults. We report for the first time, to our knowledge, that 4 wk of inorganic nitrate supplementation attenuates retrograde and oscillatory shear in the brachial artery of older adults. However, this was not associated with greater hyperemic or vasodilatory responses to exercise. In sum, these data highlight favorable changes in shear patterns with aging, which may reduce the risk of atherosclerotic cardiovascular disease.