[Changes in the urea content of blood in hypokinesia]

The blood and urine content of urea and creatinine, as well as urea production and creatinine clearance were measured in 9 test subjects exposed to head-down tilting (at -6 degrees) for 8 days. The trend for an increased urea content was more marked in the test subjects with its initially low concentration (3.3-4.2 mmole/l). Variations in the urea concentration were similar and included its decrease during the first day and increase thereafter. Creatinine excretion and clearance declined uniformly and significantly during the first 5 experimental days. No correlation was found between urea concentration and urea production, or between creatinine clearance and urea concentration.