ADENOSINE AND RENAL SODIUM HANDLING - DIRECT NATRIURESIS AND RENAL NERVE-MEDIATED ANTINATRIURESIS

Adenosine infusion is associated with natriuresis as well as antinatri uresis. The physiologic significance of these opposite effects is unkn own but may have to do with different conditions of ischemia, in which adenosine accumulates. These effects were characterized in the rat. F irst, intrarenal and systemic infusions within one animal were perform ed, Infusing 10 mu g/min into the left renal artery increased sodium b y similar to 50%; however, the subsequent infusion of 50 mu g/min into the thoracic aorta decreased sodium excretion by similar to 60%, in a ssociation with a small reduction of blood pressure. Second, to explor e the effect of intrarenal adenosine on tubular sodium handling, free- flow micropuncture experiments were performed. The intrarenal infusion of 10 mu g/min again caused sodium excretion, but no change in GFR, v olume, and sodium deliveries up to the early distal tubule was found. Apparently, the direct effect of adenosine in the kidney is sodium exc retion, by a tubular action beyond the early distal tubule. Third, to further characterize the indirect effect, which apparently is sodium r etention, adenosine was infused systemically at low rates, in order to avoid a decrease in blood pressure. A 25 mu g/min infusion again caus ed sodium retention, in the absence of a fall in blood pressure. After acute left renal denervation, the antinatriuretic effect disappeared in the denervated kidney but remained in the right kidney. These data suggest that increased intrarenal adenosine suppresses sodium reabsorp tion at some distal nephron site, appropriately decreasing the workloa d of the kidney. On the other hand, systemic adenosine stimulates sodi um reabsorption, an effect that is appropriate to improve systemic cir culation and depends on the renal nerves.