Circadian urinary citrate excretion in a rat model of exercise

AimsCircadian rhythms are the approximate 24 h biological cycles that function to prepare an organism for daily environmental changes. Circadian rhythms unquestionably play critical roles in metabolic homeostasis and the exercise has emerged as a strong non-photic time cue or zeitgeber in animal models and humans. Numerous studies about the effects of exercise on the citrate synthase activity have been published. Citrate is used to assess energy production or expenditure because it is a substrate of the Krebs Cycle, a cycle for oxidative energy production.Main methodsWe tested the existence of a rhythmic urinary citrate excretion in a rat model that is made to exercise at six different points during the day.Key findingsThe data obtained by the enzyme assays were fitted to a mathematical model (Fourier series), showing for the first time, the existence of a distinct ultradian rhythm in the urinary citrate excretion. The aerobic exercise led to the increase in the period length of the ultradian rhythm and raised the acrophase value of the urinary citrate excretion. Therefore, the urinary citrate excretion pattern changed after exercise, showing a clear circadian rhythm fitted to the mathematical model.SignificanceThe citrate urine samples could provide accurate data for ranking an individual's metabolic status. Using exercise to maintain the circadian clock at an appropriate phase and amplitude might be effective to prevent cardiometabolic disease development.