Exercise intensity and renal hemodynamics

This study investigated the effects of exercise intensity on renal hemodynamics. Three healthy male subjects underwent exercise tests on a bicycle ergometer at 7 different work loads for 15 min. The indicators of exercise intensity employed in this study were the percentage of maximal oxygen uptake (%VO₂max) and percentage of ventilatory threshold (%VT). As renal clearence parameters, para-aminohippurate clearance (C_PAH) and inulin clearance (C_IN) were measured by the continuous infusion technique. Indicators of renal hemodynamics during exercise were the percentage of C_PAH, C_IN and filtration fraction (FF) at rest. Plasma norepinephrine (NE), plasma epinephrine (E) and plasma renin activity (PRA) were measured. The best regression models between renal clearance parameters and exercise intensity were selected using Akaike's information criterion (AIC). 1) The renal clearance parameters used during exercise were %C_PAH, which determined the cubic regression model and %C_IN, which determined the quadratic regression model as the exercise intensity increased using AIC. 2) The percentage of maximal oxygen uptake at the onset of decrease in %C_PAH and %C_IN were 35 and 49%VO₂max, respectively, while %C_PAH and %C_IN began to decrease at 75 and 105%VT, respectively. Intensity of exercise at the onset of increase in %FF was 49%VO₂max or 106%VT. 3) The renal clearance parameters during exercise decreased linearly as NE, E and PRA increased. The increase in NE contributed mainly to a change in renal clearances shown by multiple regression analysis. The above results suggest that the relationship among renal plasma flow (RPF), glomerular filtration rate (GFR) and exercise intensity were demonstrated by the cubic regression model and quadratic regression model using AIC, respectively. Glomerular filtration rate and FF were maintained at the resting levels during aerobic exercise.