Possible pooling of osmotically inactive sodium in normal volunteers during extended bed rest
- Paper number
IAC-06-A1.2.06
- Author
Mrs. Irina Larina, Institute for Biomedical Problems, Russia
- Coauthor
Mrs. Tatyana Smirnova, Institute for Biomedical Problems, Russia
- Coauthor
Dr. Boris Morukov, Institute for Biomedical Problems, Russia
- Year
2006
- Abstract
To test the hypothesis about dissociation of the volumo- and osmo- regulation, we used the data of balance studies during 120 to 360-day bed rest (BR) experiments. Volunteered subjects were 30 normal males aged 21 to 40 yrs. some of whom had participated in 2-3 of these BR experiments. Water and sodium intake with food and drinks and renal excretion were daily estimated. In 120-day BR (n=20), extrarenal sodium excretion (with feces and perspiration) was also registered. In none of the BR subjects the coefficient of correlation between water and Na balance reached r=0.6; at the end of 120-day BR all the subjects exhibited losses in total body water volume as compared with baseline values; body mass reductions and negative cumulative Na balance were found in only six subjects. Eight subjects had the cumulative Na balance positive and body mass reduced; six - gained body mass or had it same as before the experiment but their sodium balance was negative. Inconsistency of the trends in Na content on the one hand, and body mass and body water volume on the other suggest that if sodium did accumulate than it could be no other but osmotically inactive. In several subjects dynamics of the water-sodium balance was on a somewhat ultradian pattern. Partly these rhythms mirrored the periodicity of sodium entry with food or intensity of exercising. However, there were subjects with low-frequency fluctuations that could not be extenuated by any of the external regular events. Infradian rhythms in the sodium balance variations lead to the supposition of a mechanism that regulates the body sodium content. This mechanism must be significantly more inert and less precise in comparison with immediate regulation of the circulating blood volume, osmolality and electrolytes ' content in plasma. Difference in the rhythmic structure of water-sodium balance among the subjects is probably related to dissociated regulation of these processes. Based on observations of the sodium balance trend in the subjects who had 2-3 extended BDs in the record, Na pooling capacity grows with age.
- Abstract document
- Manuscript document
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