Studies on the mechanism of natriuresis accompanying increased renal blood flow and its role in the renal response to extracellular volume expansion.

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Abstract
The effect of unilateral renal vasodilatation on Na excretion was studied by infusing acetylcholine into the renal artery of dogs under conditions of hydropenia (no saline load), partial saline loading, extensive saline loading, and mannitol diuresis. Unilateral increases in renal plasma flow and decreases in the extraction of PAH occurred during the infusion of acetylcholine in all 4 conditions. Unilateral increases in Na excretion without equivalent increases in filtered Na occurred during the infusion of acetylcholine in the hydro-penic and partially loaded animals. These observations are consistent with the concept that increases in renal plasma flow per se may result in decrease net tubular reabsorption of Na. In animals receiving relatively large saline loads and in animals undergoing mannitol diuresis similarly large increases in renal plasma flow during the infusion of acetylcholine did not result in further increases in Na excretion, suggesting that any effect of increased blood flow to decrease the tubular reabsorption of Na was already maximally operative under these conditions. The natriuretic effect of vasodilatation was greater in animals receiving small saline loads than in the hydropenic group, although rates of blood flow were similar in both groups. This observation is consistent with the view that small saline loads may activate natriuretic factors other than blood flow and condition the kidney for a greater (natriuretic) response to increased blood flow.