Effects of quercetin on exercise potential and exercise-induced cytokines in the horse

The goal of this experiment was to test the hypothesis that quercetin would alter markers of athletic performance as well as markers of exercise-induced inflammation. Six healthy, unfit Standardbred mares (~500 kg, age 4-5 years) were assigned to one of two treatments (quercetin or water) in an experiment conducted in a crossover fashion. The horses were dosed via a nasogastric tube twice a day (08:00 and 20:00) with either 6 g of quercetin in 2 l tap water or 2 l water for 3.5 d. Two hours after the seventh and final dose, a graded exercise test (GXT) was run. During the test the treadmill remained at a fixed 6% grade. At t=0 the treadmill was started at a speed of 4 m/s. Each following minute the treadmill speed was increased by 1 m/s, up to a maximum speed of 11 m/s. Blood and muscle samples were collected before the initial dosing, before exercise and after the GXT to measure markers of inflammation. There was a significant (P < 0.10) increase in run time to fatigue when the horses were dosed with quercetin. The VO₂ recovery time was shortened significantly when compared to water-treated trials. There were exercise-induced increases (P < 0 .10) in haematocrit and the plasma concentrations of total protein, glucose, and lactate as well as expression of mRNA for TNF-α, IL-1, interferon-γ, granzyme-B (GrB) in blood. However, quercetin only affected (P < 0.10) the expression of mRNA for GrB. Intramuscular levels of IL-1 and GrB also increased significantly with exercise, but there was no effect (P > 0 .10) from quercetin treatment. This study provides evidence that quercetin could be useful in enhancing exercise performance, although the mechanism for this enhancement is unclear.