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-coagulation of tissue containing most of the sympathetic fibres travelling towards the kidney. Kidney tissue noradrenaline was decreased to 4.7% of the content measured in the contralateral innervated kidney when studied 3 days postdenervation. 2. The method was utilised in anaesthetised rats to examine the effects of denervation within the heretofore unexplored first 75 min period postdenervation. 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 filtration rate did not change after denervation. 3. Renal cortical and medullary blood flows (CBF, MBF) were estimated as laser Doppler flux and medullary tissue ion concentration was estimated as electrical admittance( Y). Following denervation, in both groups CBF increased 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 change. 4. The data document the development of natriuresis within the first 25-50min after denervation. The increase in CBF indicated that, prior to denervation, the cortical, but not medullary, circulation was under a tonic vasoconstrictor influence of the renal nerves. Such a dissociation of neural effects on the renal cortical vs, medullary vasculature has not been previously described.