Water and sodium excretion in unilaterally denervated normal and sodium depleted anesthetized rats before and after plasma volume repletion

The possible role of a reduction in plasma volume (PV) by surgery as well as the importance of dietary Na supply in denervation natriuresis have been investigated on Inactinanesthetized male rats subjected to acute unilateral renal sympathectomy. Four groups were studied: I. Normal Na diet (n=14); II. Low Na diet (boiled rice for 2 weeks)-isotonic glucose infusion (n=10); III. Low Na diet-isotonic saline infusion (n=5); IV. Normal and low Na diet rats served as conscious control (n=10). Surgery caused a 9–11% increase in hematocrit and a 15–18% decrease in PV in groups I–III. Plasma volume repletion (PVR) reverted these changes. In group I sodium excretion from both kidneys was only a fraction of that in conscious animals kept on the same diet (group IV) and marked denervation natriuresis was observed. After PVR sodium output of innervated (I) kidneys was not different from that of conscious rats but denervated (D) kidneys excreted twice that amount. In group II Na excretion was increased compared to conscious Na depleted controls, and PVR augmented further this difference. Surprisingly, the difference in urinary sodium excretion (U_NaV) between I and D kidneys was absent after surgery and was minimal after PVR in this group. In group III physiological saline infusion reverted the effect of Na depletion and denervation natriuresis was present both before and after PVR. It is concluded that PV reduction does not play a major role in denervation phenomenon. In Na depleted anesthetized rats denervation natriuresis is absent or minimal.