The renal actions of adenosine

This study examined the effects of adenosine on the renal function. In ten normal dogs intrarenal adenosine infusion (20 nmol/kg/min) increased the renal blood flow (RBF) from 521 +/- 20 ml/min to 582 +/- 23 ml/min. The extraction of PAH (EPAH) decreased from 0.85 +/- 0.02 to 0.79 +/- 0.02, the Einulin from 0.24 +/- 0.02 to 0.18 +/- 0.02. We conclude that the intrarenal infusion of adenosine modifies the intrarenal redistribution of the blood flow increasing the deep cortical and medullary blood flow. In these experiments the glomerular filtration (GFR) during adenosine infusion calculated from the extraction of the inulin (Einulin) multiplied by the renal plasma flow (RPF) decreased from 79.4 +/- 6.4 ml/min to 62.2 +/- 6.6 ml/min and calculated from the Ecreatinine x RPF from 80.3 +/- 6.3 ml/min to 59.3 +/- 4.9 ml/min. The EPAH x RPF did not change, it was 241 +/- 11 ml/min and 253 +/- 13 ml/min, respectively. While the urinary clearances (the clearance calculated by the classic clearance formula; urinary concentration of the substance multiplied by the urine volume and divided by the plasma concentration) in the control periods did not differ from the direct clearances (Cinulin = 73.3 +/- 3 ml/min, Ccreatinine = 75 +/- 4 ml/min and CPAH = 262 +/- 15 ml/min) during the adenosine infusion there are considerable differences: the Cinulin = 40 +/- 6 ml/min, the Ccreatine = 42 +/- 6 ml/min and the CPAH = 164 +/- 22 ml/min. The differences are mathematically significant (p < 0.01). During the postinfusion periods the urinary clearances did not differ from the direct clearances. These results show that during adenosine infusion there is a definitive loss of the clearance substances somewhere in the nephron between the glomeruli and the pyelon. These observations suggest that during adenosine infusion there is a back-diffusion of the clearance substances because the permeability of the tubuli changes in the medullary part. The rediffused substances will be retransported into the circulation by the renal lymph flow and that is why they do not appear in the renal venous blood. The rediffusion can explain that the intrarenal adenosine infusion decreases considerably the excretion of the sodium and water in the kidney when there is no or only a small reduction of the glomerular filtration rate.