Study of water-salt metabolism and renal function in cosmonauts

In manned space flights the renal function and water-salt metabolism undergo substantial changes. With the reserve capabilities of kidneys in mind, their function and regulation of the water-salt balance were investigated in cosmonauts postflight and in Earth-bound simulation experiments with the aid of water loading, hormonal injections (pituitrin, engiotensin, DOCA, ACTH); water- and ion-release were also studied during LBNP and physical exercises. The cosmonauts who performed space flights of 2 to 5 days showed water retention and increased urine excretion of salts during the first postflight days in response to a water load. After the 18-day flight water excretion remained unchanged whereas salt excretion increased. The capacity for osmotic concentration and urine dilution did not alter. The study of the hormonal effect in simulation experiments of different duration demonstrated a normal renal response to the hormonal excretion. After the LBNP tests and physical exercises the water- and salt-excretion declined; a correlation between the level of water- and salt-excretion and the level of these loads was established. The data on the blood- and urine-ionic composition, excretion of nitrogen metabolites, and hormones postflight as well as the results of load and functional tests suggest that changes in the renal function of cosmonauts in weightlessness are associated with regulatory effects on the kidney rather than disturbances in the function of nephron cells.