Systemic Nitric Oxide Production and 24-Hr Blood Pressure Relationship Following Aerobic Exercise in African-American Hypertensives

Abstract

1673 We previously showed that hypertensive Caucasians significantly reduced their 24-hr ambulatory blood pressure (ABP) following acute aerobic exercise. It is not known if this type of exercise provides similar BP reductions or if the physiological mechanisms underlying this reduction are the same in African-American hypertensives. PURPOSE: To determine the effects of acute aerobic exercise on 24-hr ABP and whether changes in ABP were related to urinary nitric oxide (NO) excretion levels in African-American hypertensives. METHODS: Seventeen African-Americans with high normal blood pressure or stage 1 hypertension, but otherwise healthy, underwent 50 minutes of treadmill exercise at 65–70% of heart rate reserve. Subjects completed a 24-hr ABP monitoring and urine collection period that was divided into 5 time intervals on a day following exercise and on a day without prior exercise (baseline day). Urine samples were ultrafiltered and assayed for NO end-products (NOX) using the Greiss assay. NOX levels have been used as an index of systemic NO production. RESULTS: There were no significant differences in 24-hr mean arterial BP (MAP) between the exercise and baseline day during any of the time periods. NOX excretion was significantly greater during the first 4-hr time period on the exercise day compared to the baseline day (17.8 ± 5 μmol vs. 7.5 ± 3 μmol, p = 0.009) but not significantly different during the remaining time periods. There was no relationship between 24-h MAP and 24-hr NOX excretion on the baseline day, however there was a significant positive relationship (r = 0.32, p<0.003) during the exercise day. CONCLUSION: In contrast to similar studies in hypertensive Caucasians, acute aerobic exercise did not significantly reduce ABP in hypertensive African-Americans, indicating that the mechanisms underlying acute exercise-induced reductions in blood pressure may be different in African- Americans. It appears that acute exercise may have stimulated the NO system for the 4 hrs following exercise, however, ABP was not affected.