1. The effect of dietary sodium intake on pre-and post-prandial plasma sodium concentrations and on the pattern of sodium and potassium excretion was determined in conscious female dogs, who were allowed free access to water and were fed on commercial low sodium diets supplemented with 0, 50, 100 or 250 mmol of sodium chloride/day for 6 days.
2. The preprandial plasma sodium concentration was not altered by the dietary sodium intake. However, the 4 h postprandial plasma sodium concentration was linearly related to the magnitude of dietary sodium intake, whereas the 8 h postprandial plasma sodium concentration was elevated only in dogs receiving 250 mmol of sodium/day.
3. The (0–8 h/0–24 h) ratio for urinary sodium excretion was significantly correlated with both the dietary sodium intake and the postprandial increase in plasma sodium concentration.
4. The 24 h excretion of potassium was not markedly affected by the dietary sodium intake; however, the (0–8 h/0–24 h) ratio for potassium excretion was significantly correlated with both the dietary sodium intake and the (0–8 h/0–24 h) ratio for sodium excretion.
5. These data indicate that: (a) postprandial increases in plasma sodium concentration need to be considered when evaluating the mechanisms involved in the daily regulation of sodium balance; (b) the daily pattern of potassium excretion is closely linked to the dietary sodium intake.