Background: Animal studies have shown that nitric oxide is involved in delayed ischemic preconditioning.
Objectives: To determine whether plasma nitrates and nitrites (NO(x) (-), as measure of nitric oxide) are modified by two consecutive effort tests and whether these changes translate into clinical improvement
Methods: Twenty-two patients with ischemic heart disease each performed two effort tests at 24-h intervals. Plasma NO(x) (-) level was determined and compared before and after both stress tests. Peak effort, double product at peak effort and maximal ST segment depression were considered clinical endpoints and were compared between the two tests.
Results: Plasma NO(x) (-)increased slightly after the first exercise test compared with pretest value (17.05+/-1.6 mumol/mL versus 15.38+/-1.4 mumol/mL). In turn, after the second test there was a significant rise in NO(x) (-) level (23.65+/-2.2 mumol/mL versus 15.10+/-1.3 mumol/mL, P<0.03). The pretest values were almost identical between the two tests. Peak effort and double product at peak effort remained unchanged between the two tests. Although ischemic stress was the same, ST depression was significantly lower (P<0.01) for the second test (0.85+/-0.06 mm versus 1.73+/-0.16 mm).
Conclusion: Our study shows an increased plasma NO(x) (-)level after the second of two consecutive exercise stress tests at 24-h intervals, along with a decrease of electrocardiographic consequences of approximately the same ischemic stress. These findings are consistent with experimental data in animals, which point to nitric oxide as a trigger and effector of ischemic preconditioning.
Keywords: Delayed preconditioning; Exercise; Nitrate; Nitric oxide; Nitrite.