Abstract
We examined the effects of the amount of fluid ingestion on the renal concentrating ability during moderate exercise in a hot environment. Untrained subjects (n=6) performed 100 min of intermittent exercise on a cycle ergometer at 60% VO2max in a climatic chamber (32°C, 60% RH). The subjects were tested under the following three conditions: 1) no fluid ingestion (NF), 2) fluid ingestion in amounts equal to one-half of dehydration (FL-1%), 3) fluid ingestion in amounts equal to dehydration (FL-2%). During the NF and FL-1% trials, urine flow rate, osmolar clearance, and creatinine clearance decreased significantly (P<0.05) during exercise compared with the pre-exercise level. In addition, free water clearance was significantly (P<0.05) higher during exercise than the pre-exercise level in the NF and FL-1% trials. During the FL-2% trial, there were no significant differences in urine flow rate and osmolar, free water, and creatinine clearances during exercise compared with the pre-exercise level. On the basis of these observations, it is likely that the decrease in the tubular water reabsorption and the increase in the tubular sodium reabsorption were attenuated in the FL-2% trial. Thus, we suggest that fluid ingestion in amounts equal to dehydration is capable of attenuating the decline in the renal concentrating ability during moderate exercise. [J Physiol Sci. 2008;58 Suppl:S160]
