Urinary excretion of cytokines versus their plasma levels after endurance exercise

It has been consistently shown that circulating levels of interleukin (IL)-6, IL-8, IL-1 receptor antagonist (IL-1ra) and IL-10 increase remarkably following endurance exercise longer than 2 h such as marathon and triathlon races. However, no studies have compared changes in the plasma and urinary levels of these cytokines after endurance exercise, including the recovery period. In the present study, we investigated kinetic changes in the urinary excretion of cytokines following endurance exercise up to 3 h after exercise to evaluate the magnitude of change in comparison to the plasma levels and to explore the possible biological significance and the mechanisms of cytokine dynamics following exercise. Fourteen male athletes participated in a duathlon race consisting of 5 km of running, 40 km of cycling, and 5 km of running. Venous blood and urine samples were collected before, immediately after, 1.5 h and 3 h after the race. Plasma and urine were analyzed using enzyme-linked immunosorbent assays (ELISA). Plasma concentrations of IL-1β, IL-1ra, IL-6, IL-8, IL-10 and monocyte chemotactic protein (MCP)-1 increased significantly after the race, whereas tumour necrosis factor (TNF)-α, IL-2, IL-4, IL-12 and interferon (IFN)-γ did not change significantly. Urinary concentrations of IL-1β, IL-1ra, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IFN- γ and MCP-1 increased significantly after the race. When the urine concentrations were adjusted by creatinine concentration, urine volume and sampling time, the increases of IL-2, IL-4, IL-8, IL-10, IFN-γ and MCP-1 were evident and these were notably present in urine of the stressed athletes suffering from renal tubular epithelial damage. The present study provides new evidence that the kinetics and magnitude of changes in urinary cytokine concentrations differ from plasma cytokine concentrations following endurance exercise, especially, in the recovery period several hours after exercise, and that the damaged kidney might be responsible at least in part for the kinetics of some cytokines. Urinary cytokines may be sensitive biomarkers of the impact of exhaustive exercise workload on renal damage and inflammation in the recovery period after endurance exercise.