Reduced blood pressure responsiveness to skeletal muscle metaboreflex activation in older adults following inorganic nitrate supplementation

The vasoactive molecule nitric oxide (NO) contributes to regulation of blood pressure (BP) at rest and during exercise. Age-related exaggerated increased BP responses during exercise have been proposed to be due in part to a decreased NO bioavailability and possibly an enhanced skeletal muscle metaboreflex. In the present study we sought to determine if age-related differences in BP responses to skeletal muscle metaboreflex activation exist. Additionally, since NO bioavailability can be improved with exogenous nitrate (NO3-) via the nitrate-nitrite-NO pathway, we tested the hypothesis that inorganic NO3- supplementation would reduce BP responses to muscle metaboreflex activation in healthy older adults. 13 older adults (67 1 years) participated in a randomized, double-blind, placebo controlled crossover study consisting of four weeks of NO3- supplementation [beetroot powder; 250 mg (similar to 4.03 mmol) of NO3- and 20 mg (similar to 0.29 mmol) of NO2-] and four weeks of placebo (beetroot powder devoid of NO3- /NO2-). Skeletal muscle metaboreflex testing consisted of isometric handgrip exercise (IHG) at 30% of maximal voluntary contraction immediately followed by post exercise forearm ischemia (PEI), which was achieved by inflation of a rapid pressure cuff (240 mmHg) around the upper arm. BP responses were analyzed as the change (Delta) from baseline to the end of IHG and PEI. An additional 10 young adults (25 1 years) were recruited to serve as a reference cohort and address if BP responses to skeletal muscle metaboreflex activation were greater with aging. BP responses to IHG were similar between the young and older adults. However, older adults demonstrated a greater increase in systolic BP during PEI (P < 0.05). Plasma NO3- and NO2- were increased following NO3- supplementation in older adults (P < 0.01). Delta Systolic BP (19 +/- 2 vs. 13 +/- 3 mmHg, P < 0.05), Delta Diastolic BP (7 +/- 1 vs. 5 +/- 1 mmHg, P < 0.05) and Delta Mean arterial pressure (11 +/- 1 vs. 8 +/- 2 mmHg, P < 0.05) were reduced during PEI following four weeks of NO3- supplementation, whereas placebo had no effect on ASystolic BP (16 +/- 2 vs. 17 +/- 2 mmHg), Delta Diastolic BP (5 +/- 1 vs. 7 +/- 1 mmHg), and Delta Mean arterial pressure (8 +/- 1 vs. 10 +/- 1 mmHg) during PEI (all P > 0.05). These data suggest that inorganic NO3- supplementation attenuates skeletal muscle metaboreflex mediated increases in BP during exercise in older adults.