Specific features of water and salt metabolism during space flights of varying duration are considered in the present article. Experiments involving Russian and foreign cosmonauts/astronauts were performed in order to assess the metabolism of water and minerals, renal function, and the hormonal regulation of these processes during space flights. These in-flight experiments combined with model studies contributed to the understanding of the mechanisms of osmotic and volumetric regulation in microgravity and provided the foundations for developing prophylactic and correction procedures preventing adverse changes associated with the adaptation of the human body to the extraordinary conditions of space flight.

According to the Sprut-2 protocol, bio-impedancemetry of ISS cosmonauts was performed once a month and also before and after mission. Multiple non-invasive body measurements were carried out in 15 cosmonauts in real time. Relocation of extracellular liquid along the body axis led to its reduction in legs and, on the contrary, an increase in the abdomen. Volumes of total body liquid as well as intra- and extracellular liquids decreased in comparison with pre-flight levels. Lean body mass also became less in microgravity, whereas fat mass showed an increase.

Consumed NaCl was rationed and integral impedancemetric, psychological, and hormonal studies were performed in six male volunteers 25 to 40 years old before, during, and after an experiment with 105-day isolation and confinement. Every 30 days blood collection for hormonal measurements was combined with filling in Cattell’s 16 personality factor questionnaire. The parameters of total body fluid, body mass, basic exchange, specific hydration and basic exchange were determined. The results showed that the experimental conditions did not affect significantly the body composition, metabolism, and its neurohumoral regulation. The metabolic variations were largely associated with motivation for and value orientation in accommodation, to the permissible extent, of the controlled diet and work/rest schedule to personal needs. In addition, it was found that evolution of the psychophysiological status of humans in isolation and confinement is governed primarily by personality characteristics and, to a less degree, by the specifics and duration of exposure to the artificial environment. Thus, in the opinion of the volunteers, the normoxic, normobaric and slightly hypercapnic (0.15–0.65% CO2) atmosphere was comfortable and harmless to health. The analysis of the whole data array confirmed the expressed interrelation between neuroendocrine and psychophysiological parameters as well as shifts in body basic exchange and mass, salt intake, and hydration rate in the conditions of isolation and confinement.

The article reviews the basic problems of orthostatic tolerance and new impedance methods for evaluation of orthostatic tests during spaceflight and in simulated microgravity. The results indicate that orthostatic tolerance requires adequate body hydration and function of volume-regulating hormones. New pharmacological compensators of orthostatic intolerance were tested in model experiments. It was shown that desmopressin and water-salt supplements aid in retention of body fluids and electrolytes during bed rest and improve tolerance during orthostatic test. Therefore, a simultaneous control of hydration status and orthostatic tolerance can be best provided through physiologically reasonable prescription of synthetic antidiuretic hormone analogs.

Renal function and body composition, including fluids, were studied during space flight conditions imitation with five-day dry immersion in 14 apparently healthy men. Noninvasive research of water spaces of the body was performed using methods of bioimpedance analysis (BIA). It was shown that renal excretion of fluids increased and negative aqueous balance developed during dry immersion. Bioimpedance research revealed decreased volume of the total body and the extracellular fluids, and the amount of circulating plasma also decreased. Thus, under the conditions of immersion, hypohydration developed in the body. In the recovery period, these changes in the hydration level rapidly returned to the initial values. The lean body mass during immersion was reduced insignificantly and the amount of fat, in contrast, exceeded the baseline levels. Furthermore, the experiment showed technical impossibility to obtain reliable impedancemetry data under the dry immersion conditions.

A portable polysegment bioimpedancometer for noninvasive monitoring of human body composition (including fluid media) under spaceflight conditions is described. The device provides real-time monitoring of the dynamics of human body composition under conditions of long-term spaceflight in a space station.

The paper deals with the application of functional load tests to assess the renal function and water-salt metabolism in human subjects during spaceflight simulating experiments and in cosmonauts in orbit and in the course of postflight recovery. The tests gave insight into mechanisms of the osmotic and volumetric regulation systems and enabled the development upon this knowledge of countermeasures to correct shifts in water-salt homeostasis.

The paper deals with the application of functional load tests to assess the renal function and water-salt metabolism in human subjects during spaceflight simulating experiments and in cosmonauts in orbit and in the course of postflight recovery. The tests gave insight into mechanisms of the osmotic and volumetric regulation systems and enabled the development upon this knowledge of countermeasures to correct shifts in water-salt homeostasis.

The use of functional load tests to assess the specific features of water-electrolyte metabolism under extreme conditions is considered, with special emphasis on their implications for space physiology and medicine. Water and mineral metabolism, the kidney function, and their hormonal regulation during simulation experiments, as well as in spaceflights and in the readaptation period, play an important role in human adaptation to new conditions of vital activity. In order to assess the state of the kidneys and water-electrolyte metabolism in cosmonauts and investigators, functional load tests were developed. They enabled us not only to gain insight into the mechanisms of osmotic and volumetric regulation but also to develop countermeasures to correct unfavorable shifts in water-salt homeostasis.

The article centres on the water-salt metabolism properties in space flights of varying duration. To assess the water and mineral turnover, renal function and their hormonal regulation in flight, a series of experiments was carried out with participation of Russian and international cosmonauts. These experiments and ground model investigations shed light on the mechanisms of osmotic and volumetric regulation in microgravity and guided the development of countermeasures and methods for correcting the negative shifts as a result of body adaptation to the novel environment.

This review is focused on the redistribution of blood and other bodily fluids along the body axis in the cranial direction under conditions of microgravity or during simulation of the physiological effects of microgravity. This redistribution of bodily fluids in the direction of the thorax or head results in respective physiological responses and induces a whole cascade of secondary adaptation mechanisms. Changes in central venous pressure, heart cavity volume, kidney functioning, and hormonal volume regulation lead to adaptive modifications in bodily fluid sectors. Modification of the hemodynamic in the splanchnic vascular system influences the organs of the abdominal cavity. Pharmacological correction accelerates the adaptation of the human body to unusual living conditions.

The urine protein composition (proteome) of healthy humans was analyzed using proteomic techniques to obtain data under normal physiological conditions and after six-month space flights. It was shown that, after long space flights, specific minor proteins are revealed in cosmonauts’ urine that can be identified as proteins coming from kidneys and urinary tracts.

С помощью протеомной технологии исследован белковый состав (протеом) мочи здорового человека в обычных, физиологических условиях и после полугодовых космических экспедиций. Показано, что после полетов у космонавтов в моче выявляются специфические минорные белки, которые удалось идентифицировать и отнести к белкам, исходящим из почек и мочевыводящих путей.

A fifty-year study of water-electrolyte metabolism, the condition of the water medium of the body, and hormonal regulation during space flights and the postflight period or their on-ground modeling (hypokinesia, bed rest, immersion, etc.) has shown the important role of water-salt homeostasis in adaptation of the human and animal body to weightlessness. It has been revealed that, in weightlessness, the conditions for the development of a negative balance of a liquid (hydrohydration) and basic electrolytes are created. After termination of long space flights, attributes of the development of adaptive reactions, compensating for the loss of extracellular liquid volume come to light. In order to assess the state of the kidneys and water-electrolyte metabolism in cosmonauts and investigators, functional load tests, and special methods of diagnostics were developed. This is the basis for the research aimed at improving the scheme of correction of the water balance of the body of cosmonauts at different stages of a flight.

Изучение состояния водного и электролитного обмена, функции почек и их гормональной регуляции при космических полетах и в реадаптационном периоде, а также в модельных экспериментах (гипокинезия, иммерсия и др.) показало важнейшую роль водно-солевого метаболизма в процессах общей адаптации человека к новым условиям жизнедеятельности. В условиях невесомости и при ее имитации наблюдается гипогидратация организма и развитие отрицательного баланса основных электролитов, и особенно кальция, с повышением риска костной травмы и образования мочевых камней. После возвращения к нормальной гравитации развиваются адаптивные реакции, направленные на восполнение потерь внеклеточной жидкости. В результате 50-летних исследований разработаны методы диагностики состояния водно-электролитного метаболизма и специфические средства профилактики, направленные не только на коррекцию водно-солевого обмена, но и на повышение общей устойчивости организма.

The effects of the administration of desmopressin, a synthesized analog of antidiuretic hormone, together with a water-salt supplement on the renal function and orthostatic stability were investigated. Six healthy men spent 12 h in the head-down tilt (HDT) position. It was demonstrated that administration of desmopressin led to normalization of salt and water homeostasis; moreover, the tolerance of the standard 20 min passive standing test was improved significantly. These observations indicate that intake of the synthetic vasopressin analog combined with water-salt supplement counteracts hypohydration of the body during HDT and improved orthostatic tolerance.

The review is devoted to shifting of blood and other liquids along the body axis toward the cranium end in microgravity and during simulation of the zero-g physiological effects. The body liquids redistribution excites a number of consistent physiological reactions as well as a cascade of secondary adaptation processes. Changes occur in central venous pressure and size of the heart cavities, renal function and hormonal volumoregulation entailing the adaptive shifts in body liquid segments. Hemodynamic changes in the splanchnic vascular system affect functioning of the abdominal organs. Measures of pharmacological correction expedite human adaptation to unusual environments.

Renal function and body composition, including liquids, were investigated in 14 essentially healthy male subjects during simulation of some spaceflight effects by 5-d dry immersion (DI). Noninvasive measurement of water spaces of organism was performed with the methods of bio-impedance analysis (BIA). Increase of renal excretion of liquids and appearance of negative water balance were observed. BIA revealed reductions of total body and extracellular liquids and a decrease of circulating plasma volume. This means, that DI induced hypohydration of organism. In the post-DI period, the hydration status regained its baseline level fairly soon. Lean body mass slightly decreased; adipose mass, on the contrary, exceeded baseline values. Moreover, the experiment evidenced technical impossibility to obtain valid impedansimetry data in DI.

Effects of desmopressin, a synthetic analog of antidiuretic hormone (ADH), on water-salt metabolism and orthostatic tolerance were evaluated in human subjects during 24-hr HDT (-15 degrees). Consumption of the preparation was found to dampen losses in total body and extracellular liquids and to slow down diuresis as well as establishment of a positive water balance as compared with control series without ADH. In addition, tolerance of the standard standing test improved noticeably. To conclude, desmopressin precluded hypohydration of the tilted subjects and, consequently, prevented loss of orthostatic tolerance.