Expression of the inducible nitric oxide synthase (iNOS) in human leukocytes: responses to running exercise

Introduction: We examined the influence of two different bouts of vigorous running exercise on the expression of the inducible nitric oxide synthase ( iNOS) in leukocytes (LE). Methods: In study 1, 10 trained runners competed in a half marathon (HM) lasting 90.5 +/- 11.0 min. In study 2, 8 untrained subjects performed a graded treadmill test followed by a continuous run (CR ) until exhaustion (11.3 +/- 1.3 min). iNOS mRNA levels were assessed by RT /PCR at rest, 0, 3, and 24 h after HM and CR. In study 2, iNOS was addition ally analyzed at the protein level in lympho- (L), mono- (M), and granulocy tes (G) by flow cytometry at rest and up to 48 h after CR. Results: Analysi s revealed a rise of the iNOS transcript directly after the HM in 8 of 10 s ubjects. In study 2, the expression of iNOS protein at rest differed betwee n L (mean +/- SE: 30.9 +/- 4.5% iNOS positive cells), M (91.3 +/- 4.0%), ad d G (64.9 +/- 10.3%): 3 h after CR, expression of iNOS increased in L (67.3 +/- 7.4%) and G (90.3 +/- 2.9%) and was still elevated 48 h post-exercise. However, our measurements failed to detect significant changes of leukocyt e iNOS mRNA in response to CR. After the HM, our findings were paralleled b y elevated plasma levels of interleukin-8, myeloperoxidase (MPO), and partl y of TNF-a, whereas CR only induced a low rise of MPO. Conclusion: Our inve stigations revealed an increased expression of iNOS at the transcriptional and translational level in response to vigorous exercise. This reflects an inflammatory response and may contribute to an exercise-induced rise of end ogenous nitric oxide production. It remains unclear if these effects serve an in-vivo immunoregulatory or cell-damaging role.