Effect of physical exercise on renal response to head-out water immersion.

Head-out water immersion (HOI) induces various renal functional changes, such as diuresis, natriuresis, and kaliuresis. The present study was undertaken 1) to characterize the renal response to HOI in Koreans who routinely ingest high salt diet and 2) to evaluate the impact of exercise on the renal response to HOI. Six healthy male subjects (average Na+ intake of 232 mEq.day-1) were immersed upto the neck in 34.5 degrees C water and rested in a seated position or exercised on a bicycle ergometer for 3 hours. In resting subjects, we observed a reversible increase in urine flow and a decrease in urine osmolality, with no changes in creatinine clearance. The peak urine flow observed during the second hour of immersion was 4-fold greater than the pre-immersion level. The excretion of total osmotic substances rose progressively during the 3-hour immersion, which was accompanied by a similar change in Na+ excretion. The K+ excretion was slightly elevated. The major component of the immersion diuresis was a water diuresis in the early phase and an osmotic diuresis in the late phase of immersion. In exercising subjects, the diuretic and natriuretic responses to HOI were attenuated and the kaliuretic response was potentiated. Blood hemoglobin concentration and plasma levels of renin, ADH, and aldosterone decreased during immersion-rest, but they remained unchanged or increased during immersion-exercise. These results suggest that 1) the cardiac mechanoreceptor-mediated renal responses to HOI are not changed by chronic high salt diet, and 2) excessive urinary sodium and water losses are prevented by exercise during immersion.