[Metabolic characteristics during 120-day head-down tilt hypokinesia]

Nine healthy test subjects, aged 25 to 44 years, were exposed to bed rest (at -5 degrees) for 120 days. Venous blood and 24-hour urine samples were used to measure Na, K, total and ionized Ca, Mg, total protein, protein fractions, creatinine, urea, uric acid, malate, isocitric and lactate dehydrogenases, aspartate and alanine aminotransferases, and creatine phosphokinase and its isoforms, acid and alkaline phosphatase and its isoenzymes. Prolonged exposure to head-down tilting resulted in a negative balance of fluid and electrolytes, lowered concentration of total protein and albumins, and an increased concentration of urea and creatinine, basic products of protein metabolism. In blood, the activity of dehydrogenases of the tricarboxylic acid cycle and creatine kinase decreased at the expense of its muscle isoenzyme and the activity of acid phosphatase, total alkaline phosphatase and bone isoenzyme of alkaline phosphatase increased.