Aldosterone and the enhanced natriuresis of hypertonic infusions in the dog

The purpose of this study was to determine whether small elevations in plasma sodium concentration (PNa) were effective in decreasing aldosterone secretion and, hence, in increasing sodium excretion in dogs fed normal sodium diets. Ten dogs fed a normal sodium diet, six DOCA-treated dogs, and four adrenalectomized dogs were given the same sodium load (2.5 mmol/kg) either as a hypertonic (1 M NaCl) or hypotonic (0.1 M NaCl) infusion. In all three groups of dogs, PNa was greater after the hypertonic than after the hypotonic infusion during most of the 22-h experiment. The dogs fed a normal sodium diet responded to the elevation in PNa (hypertonic infusion) with decreased aldosterone excretion and an exaggerated natriuresis. When aldosterone levels were maintained constant by either DOCA treatment or adrenalectomy, the exaggerated natriuresis that accompanied the hypertonic infusion was prevented. Therefore, elevation of PNa appears to be an important determinant of aldosterone secretion and, hence, of sodium excretion in conscious dogs fed normal sodium diets.