[Effect of horizontal immersion into water at 38 degrees C on the urinary elimination of catecholamines]

The urinary excretion of noradrenaline, adrenaline and creatinine has been studied in normal young individuals during a water bath at 38 degrees C for 40 minutes. The noradrenalinuria and the ratio noradrenalinuria/creatininuria are decreased, indicating an inhibition of the vasomotor activity of the orthosympathetic system. This inhibition is related to the consequence of the external hydrostatic pressure of the water filling the intrathoracic venous reservoirs and increasing the systemic blood pressure at the sino-baroreceptor level, hyperthermia playing a very limited role.