Introduction: 

Nitric oxide (NO) functions as a potent regulator of vascular tone. NO may serve as a modulator of overall microvascular integrity, function and oxygen transport. The synthesis of NO has been attributed exclusively to endothelial cells. Recently, red blood cells (RBCs) have been shown to express a functional eNOS isoform and thus seem to play a crucial role in NO generation. Acute and/or chronic exercise and especially the resulting shear stresses are important stimuli for NO production in endothelial cells. It is still unknown whether exercise influences the regulation of erythrocyte eNOS content and activity. It is well-established that physical exercise affects the plasma membrane of RBCs and thus impairs RBCs' deformability, which in turn reduces the oxygen supply in peripheral capillaries. Therefore, the present study aims to investigate the possible influence of a two-day long highly intensive training camp on the eNOS isoforms and phosphorylation states in human RBCs.Methods:

Twelve male international-class hockey players (26.33.7 years) participated in this study. A two-day lasting highly intensive training camp was conducted to prepare for an international competition. Several training sessions were carried out each day. Blood samples were taken before the training and after the training camp. eNOS content and activities of its phosphorylation states were analyzed by immunohistochemical procedures.Results:

Compared to the pre-training camp status the eNOS content was decreased after the training camp. Comparable to these results, activated eNOS was also decreased after the training camp. The eNOS phosphorylation site Ser1177 showed decreased activities after the training camp in human RBCs. The same picture was observed by analyzing the nitrotyrosine, which is formed by NO and superoxide, level after training camp. In contrast, eNOS phosphorylation sites Ser116 and Thr495 did not show any differences after the training camp compared to the pre-training camp situation.Discussion:

The present data show that intensive physical exercise might be a crucial regulator of eNOS content and eNOS phosphorylation in human erythrocytes. As demonstrated in the present study, highly intensive exercise can impair eNOS content and subsequently activated eNOS phosphorylation states. Further studies are needed to provide differentiated insights to eNOS regulation in human erythrocytes depending on exercise input. The present results may also have a clinical importance, because eNOS regulation in human RBCs might be dependent on exercise intensity.