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

Abstract

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. 10 older adults (67±3yrs) consumed 4.03mmol nitrate and 0.29mmol nitrite (active) or devoid of both (placebo) daily for 4wks in randomized, double-blinded, crossover fashion. Brachial artery diameter (D) and blood velocity (Vmean) were measured via Doppler ultrasound at rest for the characterization of shear profile as well as during two handgrip exercise trials (4 and 8kg) for calculation of forearm blood flow (Vmean*cross-sectional area, FBF) and conductance (FBF/mean arterial pressure, FVC). Plasma [nitrate] and [nitrite] increased following active (P<0.05 for both) but not placebo (P=0.68 and 0.40, respectively) supplementation. Neither mean nor antegrade shear rate changed following either supplement (beverage-by-time P=0.14 and 0.21, respectively). Retrograde (-13.4±7.0 to -9.7±6.8s-1) and oscillatory (0.20±0.08 to 0.15±0.09A.U., P<0.05 for both) shear decreased following active, but not placebo (P=0.81 and 0.70, respectively), supplementation. The FBF response (Δ from rest) to neither 4kg nor 8kg trials changed following either supplement (beverage-by-time P=0.53 and 0.11, respectively). Similarly, no changes were observed in FVC responses to 4kg or 8kg trials (beverage-by-time P=0.23 and 0.07, respectively). These data indicate inorganic nitrate supplementation improves conduit artery shear profiles, but not exercise hyperemia, in older adults.