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Two groups of 5 healthy volunteers each were exposed for 7 days to: 1) group 1 to horizontal bed rest and 2) group 2 to head-down tilt at -6 degrees. The purpose of the study was to determine the effect of body position on fluid-electrolyte metabolism and renal function. During the control period (14 days), bed rest and the recovery period the consumption of fluids and mineral substances and their renal excretion were measured. The typical changes in fluid-electrolyte metabolism during head-down tilt developed faster than during horizontal bed rest. The fluid-electrolyte balance became negative in the course of the exposure and returned to normal during the recovery period. The group 2 subjects showed greater body weight losses due to both fluid and muscle mass losses.

It was demonstrated that a prolonged (24 days) bed rest at altitudes of 2200 m and 3200 m as well as at sea level was accompanied by an increased renal excretion of fluids and osmotically active substances, including electrolytes. Exercises done during bed rest indiced a smaller increase of the renal excretion of sodium and potassium. However, as bed rest continued the differences between the groups of test subjects disappeared. The levels of hypoxia and exercises used in the study proved inefficient to prevent changes in the fluid-electrolyte metabolism occurring during bed rest.

The paper presents the results of studying fluid-electrolyte metabolism and the renal function in A. A. Gubarev and G. M. Grechko after their 30-cay orbital flight. On the R + O day renal excretion of fluid, sodium, potassium and osmotically active subtances decreased. Renal excretion of calcium and magnesium postflight was higher than preflight. Similar, although better pronounced, changes were seen during provocative tests with a water load. One of the factors causing changes in the renal transport of electrolytes postflight could have been an alteration in the ionic composition of the serum, especially a decrease in the potassium concentration and an increase in the calcium and magnesium content. Disorders in the relationship between the function of osmo- and ion regulation systems and dissociation in the renal excretion of individual ions after the 30-day flight that were distinct during tests with a water load seem to be associated with metabolic changes during and after flight rather than with hemodynamic changes.

The influence of anabolic steroids on the fluid-electrolyte metabolism and renal function of man was studied during a prolonged bed rest experiment. Seven test subjects were kept under surveillance. Three test subjects were given nerobol and four subjects served as controls. The fluid-electrolyte metabolism and the osmoregulatory function of the kidneys were studied. Nerobol induced a decreased excretion of sodium, potassium, calcium, chlorides and osmotically active substances. Nerobol produced the most pronounced effect on the calcium and potassium metabolism. The effect of the drug used during the prolonged bed rest experiment depended on the time and dosage as well as on the state of fluid-eletrolyte metabolism and the renal function.

The paper describes the effect of exercises, LBNP, controlled water and salt consumption, and drugs used as countermeasures against cardiovascular deconditioning during prolonged (2--7 weeks) head-down bed rest. Each of the above countermeasures applied separately had a limited effect. The use of a combination of exercises, LBNP and water-salt supplements at the final stage of the bed rest experiment made it possible to prevent entirely deterioration of work capacity and decrease of orthostatic tolerance of the test subject. The paper presents the scheme and regimens of the above countermeasures employed to meet the requirements of the flights of the orbital station "Salyut".

The paper presents the results of studying the fluid-electrolyte metabolism in P. I. Klimuk and V. I. Sevastyanov before and after their 63-day flight aboard the orbital station Salyut-4. Postflight weight losses in P.I. Klimuk and V.I. Sevastyanov were 5.6 and 3.5%, respectively, the losses being attributed to body dehydration. Postflight both cosmonauts showed a trend for an increased renal excretion of potassium, magnesium, and calcium as compared with their food intake. Those were more expressed on the day after the water load application. Possible causes of the changes and the pattern of recovery of fluid-electrolyte metabolism after a prolonged space flight are discussed.

Sodium balance and circulating plasma, intracellular, extracellular and interstitial fluid volumes were measured in the test subjects exposed for 120 days to head-down tilt at -5 degrees. The large scatter of the above parameters was associated with individual variations and with the use of different countermeasures against demineralization (exercise and drugs-xydiphone and glucamak). The effect of the countermeasures was different both in qualitative and quantitative terms. It appears that the target of their action was different. The best prophylactic effect was seen when exercise and drugs were used in combination. These findings suggest that individual variations of fluid-electrolyte metabolism during prolonged hypokinesia are related to the different capacity of tissues for water and electrolytes.

The water-salt supplement developed in ground-based experiments in order to increase human tolerance to LBNP and orthostatic tests was recommended to be given to the crewmembers at the final stage of the second expedition of Salyut-4. On the 53rd flight day, concomitantly with an intake of 4.0 g sodium chloride and 900-1200 ml water, an LBNP test was carried out to assess the effectiveness of this supplement, to select its optimal doses and to clarify individual responses. After the intake both cosmonauts showed a better tolerance of the LBNP test. They also displayed individual variations in their responses, viz. the commander in arterial circulation, and the flightengineer in venous circulation. As suggested by the ground-based experiments and the inflight provocative test, both cosmonauts were requested to take 9.0 g sodium chloride and 1000--1200 ml water on the last flight day. The postflight examinations demonstrated that the countermeasures applied (physical exercises, LBNP) in combination with the direct action on the fluid-electrolyte metabolism gave a pronounced positive effect.