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Publication AbstractsEffect of Dietary Sodium on Fluid/Electrolyte Regulation During Bed RestW. Jon Williams, Suzanne M. Schneider, Randall J. Gretebeck, Helen W. Lane, Charles A. Stuart, and Peggy A. WhitsonAviat Space Environ Med 2003; 74:37-46 AbstractBackground: A negative fluid balance during bed rest (BR) is accompanied by decreased plasma volume (PV) which contributes to cardiovascular deconditioning. Hypothesis: We hypothesized that increasing dietary sodium while controlling fluid intake would increase plasma osmolality (POSM), stimulate fluid conserving hormones, and reduce fluid/electrolyte (F/E) losses during BR; conversely, decreasing dietary sodium would decrease POSM, suppress fluid conserving hormones, and increase F/E losses. Methods: We controlled fluid intake (30 ml · kg-1 · d-1) in 17 men who consumed either a 4.0 ± 0.06 g · d-1 (174 mmol · d-1) (CONT; n = 6), 1.0 ± 0.02 g · d-1 (43 mmol · d-1) (LS; n = 6), or 10.0 ± 0.04 g · d-1 (430 mmol · d-1) (HS; n = 5) sodium diet before, during, and after 21 d of 6° head-down BR. PV, total body water, urine volume and osmolality, POSM, and F/E controlling hormone concentrations were measured. Results: In HS subjects, plasma renin activity (-92%), plasma/urinary aldosterone (-59%; -64%), and PV (-15.0%; 6.0 ml · kg-1; p < 0.05) decreased while plasma atrial natriuretic peptide (+34%) and urine antidiuretic hormone (+24%) increased during BR (p < 0.05) compared with CONT. In LS, plasma renin activity (+166%), plasma aldosterone (+167%), plasma antidiuretic hormone (+19%), and urinary aldosterone (+335%) increased with no change in PV compared with CONT (p < 0.05). Total body water did not change in any of the subjects. Conclusions: Contrary to our hypothesis, increasing dietary sodium while controlling fluid intake during BR resulted in a greater loss of PV compared with the CONT subjects. Reducing dietary sodium while controlling fluid intake did not alter the PV response during BR compared with CONT subjects.Keywords: fluid and electrolyte hormones, plasma volume, total body water, osmolality. Information on subscribing, and on obtaining copies of an article or of an entire issue. Table of Contents for Volume 74, Number 1 of the ASEM journal.
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