Effects of chronic renal denervation in conscious restrained rats

Sodium (Na), calcium (Ca), inorganic phosphate (Pi) and water excretion were measured in nondiuretic (ND) and extracellular fluid (ECF) volume expanded (VE) conscious restrained rats four weeks after denervation or sham-denervation of the left kidney. On the day of the study the animals were lightly anaesthetized with ether and the femoral vessels on one side were catheterized. Urine was collected from both kidneys. The animals were allowed to recover for 3 hours and studied in a restraining chamber. In ND animals isotonic saline containing inulin and para-amino-hippuric acid (PAH) were given at a rate of 0.067 +/- 0.002 (SE) ml/min/kg body weight (BW). In VE animals the infusion rate was 0.24 +/- 0.04 ml/min/kg BW. Kidney catecholamine content was measured after the experiments. Clearances of PAH and of inulin (GFR) were the same in both kidneys. Urine volume (V), sodium excretion (UNa V/GFR), inorganic phosphate excretion (UPi V/GFR) and calcium excretion (UCa V/GFR) were significantly higher in the denervated kidneys. Values in sham denervated kidneys were not greater than those of the right kidney. Denervation was proven by demonstrating absent or very low catecholamine content in the kidneys. The results demonstrate that: chronic renal denervation in rats leads to diuresis and natriuresis even in the conscious state, thus confirming previous results from our laboratory; such changes occur independently of the state of the ECF volume and of renal haemodynamic changes; the increased excretion of Ca++ and Pi after denervation demonstrates that renal nerves affect the reabsorption of these ions either independently or by way of their effect on sodium reabsorption. These data allow us to suggest that a renal tubular dysfunction, which was proved in anaesthetized denervated animals, can also be observed in the conscious state.