Abstract Background and Objective: Endothelial function is considered an important biomarker for cardiovascular health. This tissue controls important functions such as vascular tone regulation through the production and release of mediators such as nitric oxide and endothelin-1. Prevention of endothelial dysfunction can be effectively managed through physical activity. However, attention to the time of exercise and circadian rhythm is very important, therefore, this study aimed to investigate the differences between morning and evening exercise in the production of nitric oxide and plasma endothelin-1. Methods: In this quasi-experimental study, 40 healthy men aged 50 to 60 years were randomly divided into two groups of 20 each, training in the morning and evening, and participated in a walking program with an intensity of 65 to 70% of maximum heart rate for 12 weeks, three sessions per week. Venous blood was collected as pre-training data before the start of the training protocol, and blood was collected again after 12 weeks. The data analyzed included plasma NO and ET-1. Covariance and paired t-tests with a significance level (p≤0.05) were used in SPSS version 27 software. Results: Plasma NO levels increased significantly in both exercise groups (0.9 pg/mL in the morning group and 1.06 pg/mL in the evening group, p<0.01), however, no significant difference was observed between the morning and evening groups (p>0.05). Plasma ET-1 levels also decreased significantly in both groups (1 pg/mL in the morning group and 1.26 pg/mL in the evening group, p<0.01), but this decrease was greater in the evening group (p<0.05). Conclusion: Walking, as a moderate-intensity aerobic activity, appears to be effective in improving endothelial function by increasing NO and decreasing ET-1. However, performing exercise in the evening is more effective than in the morning, with a significant decrease in ET-1.
Sepehri Manesh M, Fathi M, Rezaei R. Comparison of the effects of morning and evening walking on plasma levels of nitric oxide (NO) and endothelin-1 (ET-1) in healthy middle-aged men. armaghanj 2026; 31 (1) URL: http://armaghanj.yums.ac.ir/article-1-3882-en.html