SODIUM-INTAKE MARKEDLY ALTERS RENAL INTERSTITIAL FLUID ADENOSINE

Adenosine is produced locally in the kidney. Accumulating data suggest that adenosine plays a role in regulating renal functions. Using a mi crodialysis technique, we monitored adenosine levels in cortical and m edullary renal interstitial fluid and urine after 5 days of diets cont aining low (0.15%), normal (0.28%), and high (4.0%) sodium. Samples we re collected from anesthetized rats (n=5 for each diet). Microdialysis fluid was infused at a rate of 1 mu L/min. Adenosine, measured by rad ioimmunoassay, was stable in the diary sate. During normal sodium inta ke, renal interstitial fluid adenosine estimated from the concentratio n in dialysate leaving the cortex was 63+/-6 nmol/L, which was signifi cantly lower than in dialysate leaving the medulla (157+/-6 nmol/L, P< .01). The concentration of interstitial medullary adenosine was estima ted to be 190 nmol/L. In rats consuming a low sodium diet, renal corti cal and medullary dialysate adenosine concentrations were significantl y decreased (P<.01) by 62.6% and 64.9%, respectively. Rats consuming a high sodium diet had renal cortical and medullary dialysate adenosine concentrations that were increased 18.2- and 18.9-fold, respectively (P<.01), compared with levels in rats on a low sodium diet. Similar to changes in dialysate adenosine, urinary adenosine concentration decre ased during low sodium intake (P<.01) and increased during high sodium intake (P<.01). The higher adenosine levels in renal medullary than i n cortical interstitial fluid may reflect its major renal site of gene ration. The changes in renal adenosine generation with sodium intake m ay reflect renal energy expenditure.