Early effects of renal denervation in the anaesthetised rat: natriuresis and increased cortical blood flow

1. A novel method of renal denervation was developed based on electro-coagu lation of tissue containing most of the sympathetic fibres travelling towar ds the kidney. Kidney tissue noradrenaline was decreased to 4.7% of the con tent measured in the contralateral innervated kidney when studied 3 days po stdenervation. 2. The method was utilised in anaesthetised rats to examine the effects of denervation within the heretofore unexplored first 75 min period postdenerv ation. Sodium excretion (U-Na(V) over dot) increased significantly (+82 %, P < 0.03) over the 25-50 min after denervation. In a parallel group, with a lower baseline U-Na((V) over dot) there was also a significant increase in U-Na((V) over dot) Ti (+54%, P < 0.03) within the first 25 min. The renal perfusion pressure was maintained at a constant value and the glomerular fi ltration rate did not change after denervation. 3. Renal cortical and medullary blood flows (CBF, MBF) were estimated as la ser Doppler flux and medullary tissue ion concentration was estimated as el ectrical admittance( Y). Following denervation, in both groups CBF increase d significantly within the first 25 min (+12%, P < 0.01, and +8 %, P < 0.05 , respectively) while MBF did not change or decreased slightly; Y did not c hange. 4. The data document the development of natriuresis within the first 25-50m in after denervation. The increase in CBF indicated that, prior to denervat ion, the cortical, but not medullary, circulation was under a tonic vasocon strictor influence of the renal nerves. Such a dissociation of neural effec ts on the renal cortical vs, medullary vasculature has not been previously described.