Effects of alpha-adrenergic blockade on sodium excretion in normal and chronic salt retaining dogs

The alpha-adrenergic blocking agent phenoxybenzamine (PBA) was administered intravenously (10 mug kg-1 min-1) during a steady state water diuresis under pentothal anesthesia to six normal dogs, six dogs with chronic throacic inferior vena cava constriction and ascites (caval dogs) and seven dogs chronically salt depleted by sodium restriction and furosemide administration. In normal dogs urinary sodium excretion increased significantly from 265+/56 (SEM) to 370+/65 muequiv./min, whereas no increase in sodium excretion was noted in either caval dogs or salt depleted animals after PBA. In all three groups urine volume, fractional free water clearance and distalsodium load did not change significantly. In normal dogs, tubular sodium reabsorption decreased significantly from 73.4+/2.8% to 63.1+/4.0%, whereas no change was noted in caval or salt depleted dogs. Blood pressure and renal hemodynamics were not significantly altered by PBA administration in any group. These data demonstrate a natriuretic effect of alpha-adrenergic blockade in normal dogs with the major effect in the water clearing segment of the nephron. The absence of any effect in chronic caval or salt depleted dogs suggests that increased alpha-adrenergic activity does not play a significant role in the sodium retention of these animals.