Background: Our aim was to compare the effects of exercise on systemic nitric oxide formation, assessed from the urinary excretion rates of nitrate and of cyclic GMP, in endurance-trained and untrained men.

Methods: Ten endurance-trained and six untrained men underwent a submaximal exercise test for 30 min at 60% of their individual maximal work capacity. Urinary excretion rates of nitrate (measured using gas chromatography) and cyclic GMP (measured using a radioimmunoassay) were assessed at hourly intervals.

Results: Urinary nitrate excretion was comparable at rest in the two groups (104 ± 35 and 110 ± 19 μmol/mmol creatinine; NS), more than doubled during exercise in both groups (236 ± 88 μmol/mmol creatinine in untrained and 252 ± 39 μmol/mmol creatinine in trained participants; P <0.01 for both groups) and decreased rapidly after the completion of the exercise test. Excretion of urinary cyclic GMP at rest was four times higher in the endurance-trained than in the untrained men (21 ± 5 compared with 6 ± 1 nmol/mmol creatinine; P <0.05). During the exercise test, GMP excretion approximately doubled in both groups (52 ± 12 and 10+1 nmol/mmol creatinine, respectively; P <0.01 for both groups) and returned to baseline at the end of the test. Urinary cyclic GMP and nitrate excretion correlated well in both groups (P <0.05). Atrial natriuretic factor is also a stimulator of cyclic GMP formation but resting plasma levels of atrial natriuretic factor did not differ between the groups (22 ± 3 compared with 21 ± 4pmol/l; NS).

Conclusion: An acute submaximal exercise test increases the formation of nitric oxide, reflected in the increase in urinary excretion of nitrate and cyclic GMP. This increase may contribute to vasodilatation during physical exercise and at least partly explain the beneficial effects of physical training in patients with vascular diseases.