Repletion of acute sodium deficit in rats drinking either low or high concentrations of sodium chloride solution

These studies investigate the relationship between expression of sodium appetite and restoration of physiological normalcy after acute sodium depletion in Sprague-Dawley rats. After depletion (treatment with diuretic and 24 h without NaCl), separate groups of rats were allowed to drink either a low (0.03 M) or a high (0.3 M) concentration of NaCl. Intake and urinary output of sodium and selected plasma measures were made at various times up to 48 h. Depleted rats with access to 0.3 M NaCl consumed more Na+ than their deficit in the first hour and were volume expanded as a result of this excessive intake, but they continued to consume NaCl for 6-12 h. Depleted rats given 0.03 M NaCl drank a comparable volume to the 0.3 M group in the first hour and thus only approximately 10% of the solute. The intake of 0.03 M NaCl slowed after 6-12 h, at which time the cumulative intake matched the deficit and the plasma parameters had returned to nondepleted levels. Under these conditions of slow intake, it appears that sodium appetite is more closely matched to need than is the case when highly concentrated sources of sodium are available. Satiation of sodium appetite seems to require the passage of time as well as repletion of body sodium.