[Ion-regulating function of the human kidneys during prolonged space flight and in simulation studies].

Ten cosmonauts who performed 30- to 175-day space flights on board Salyut-4 and Salyut-6, and 50 test subjects exposed to head-down tilt (-4 degrees) for 182 days were examined. In actual and stimulated weightlessness renal excretion of calcium and potassium increased, reaching maximum during the 4-6th weeks. Before and after flight the test subjects were exposed to loading salt tests. Renal excretion of calcium and potassium in response to the loading tests with their salts postflight was much higher than preflight. During the potassium chloride load the aldosterone content in blood correlated with potassium excretion, and during the calcium lactate load an increase in calcium excretion was paralleled by a decrease in the parathormone content in blood. It is most likely that the negative balance of ions in weightlessness is associated with the reduced capacity of tissues to retain electrolytes due to the decreased ion pool. It was shown that electrolyte balance can be beneficially influenced by exercises.