Sodium excretion in normal conscious dogs

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Abstract
Dogs maintained on a low Na intake were given doses of saline (0.125 mol/l NaCl, 0.025 mol/l NaHCO3, 0.004 mol/l KCl) by gastric tube. Doses of 100 and 200 ml produced only minor increases in Na excretion; after 300 ml, Na excretion rose from about 2 to about 60 .mu.mol/min. Plasma protein fell by 1.8 g/l for each 100 ml of saline retained. Within normal ranges of Na excretion there is a threshold of plasma protein concentration above which Na is retained and below which Na is excreted. Changes in exogenous creatinine clearance were calculated allowing for the filtered load of Na, demonstrating that absolute tubular reabsorption of Na and H2O is increased in volume expansion by isotonic saline. A diet of meat produced large increases in glomerular filtration rate without much increase in Na excretion. Mechanisms are discussed by which Na reabsorption is more effective after meat than after doses of saline. Creatinine clearance increased by 0.67 ml/min for each 1 g/l decrease in plasma protein; this supports a theory that the rate of glomerular capillary blood pressure is 9.3 kPa [kilopascals] (70 mmHg) rather than 6.7 kPa (50 mmHg).