Effect of exercise on occurrence of diurnal rhythms of plasma ions and metabolites in Thoroughbred racehorses

Abstract

Records of plasma calcium (Ca ++ ), phosphorus (P i ), potassium (K + ), sodium (Na + ), chloride (Cl -), magnesium (Mg ++ ), iron (Fe ++ ), glucose, cholesterol, triglycerides and total protein levels were measured to determine the effects of exercise on occurrence of diurnal rhythms in Throughbred racehorses (n=7) under physical training. Physical activities consisted of gallop on the track and walking. Blood samples were collected from jugular vein every 4h over a 48h period. Plasma Ca ++ , K + , Mg ++ and Na + levels were obtained by flame photometry; and, P i , Cl -, Fe ++ , glucose, cholesterol, triglycerides and total protein levels were measured by colorimetric tests using visible UV spectrophotometry. The data were analyzed using a 24h period to each exercise performed. Diurnal rhythm of Pi was observed when walking was the physical activity performed, and its acrophase occurred at the light period. Plasma triclycerides showed significant diurnal rhythms, with their acrophases occurring at the dark period, even when walking or gallop were performed. High intensity exercise (gallop) decreased triglycerides amplitude. No significant diurnal rhythms of other variables were found. Gallop, as physical activity, masked phosphorus diurnal rhythm. However, physical training did not influence triglycerides diurnal rhythm occurrence. High intensity exercise (gallop) just declined triglycerides amplitude.