Urinary excretion of nitric oxide metabolites in runners, sedentary individuals and patients with coronary artery disease: effects of 42 km marathon, 15 km race and a cardiac rehabilitation program.

BACKGROUND

The mechanisms by which regular exercise is associated with decreases in all-cause and cardiovascular mortality are unknown. Nitric oxide (NO) may have a role, as it is known to be an important factor in cardiovascular regulation. The relationships between physical activity and systemic formation of NO were evaluated in healthy volunteers and in patients with coronary artery disease (CAD).

METHODS

Urinary excretion of NO metabolites (nitrates + nitrites) was measured in 50 men. Group 1 comprised 14 highly trained runners (90 km/week) who were tested before and after a marathon race of 42.2 km. Group 2 comprised 11 well trained men (64 km/week) who were tested before and after a 15 km race. Group 3 comprised 12 sedentary individuals who gave a single urine sample. Group 4 comprised 13 patients with CAD who were tested before and after a 6 km walk.

RESULTS

Group 1 showed the highest basal levels of urinary NO metabolites: 10.10 mmol/g creatinine; they were followed by group 2, with 5.60 mmol/g creatinine, group 3 with 1.59 mmol/g creatinine and patients with CAD (group 4), who had 0.35 mmol/g creatinine. After the marathon, those in group 1 showed a significant (P=0.0001) reduction of 80% in the excretion of NO metabolites. The 15 km race (group 2 and the 6 km walk (group 4), produced nonsignificant reductions in NO excretion. Patients with CAD were prospectively evaluated before and after a 12-week cardiac rehabilitation program. Their urinary excretion of NO metabolites (mmol/g creatinine) at the end of the program was 157% higher than at baseline (P=0.034). A positive, significant correlation (P=0.006) was observed between the increases in exercise capacity [in METs (one MET is equal to the body's oxygen consumption at rest, and corresponds to 3.5 ml/Kg/min)] and in NO metabolite excretion induced by the 12-week program.

CONCLUSIONS

The baseline urinary excretion of NO metabolites increases with increasing levels of physical activity (chronic aerobic exercise). Patients with CAD had lowest levels of urinary NO metabolites and these increased in direct proportion with the gain in functional capacity. These findings suggest that increased NO production may be a major adaptive mechanism by which chronic aerobic exercise training benefits the cardiovascular system. The marked increase in NO production induced by long-term, high levels of aerobic exercise may be protective in athletes undertaking strenuous levels of exercise.