Effect of bradykinin on the renal medullary osmotic gradient in water diuresis

The effect of bradykinin on the renal medullary osmotic gradient was evaluated in anesthetized dogs which were undergoing water diuresis and which received a unilateral renal arterial infusion of bradykinin. The effect of the peptide on the medullary osmotic gradient was determined by analysis of medullary tissue electrolyte and urea concentrations and by analysis of changes in urine osmolality induced by vasopressin. Bradykinin decreased the total osmolality per kg H2O in tissue from inner medulla and papilla (-18.7 +/- 6% and -19.3 +/- 8%) and increased fractional water excretion (3.8 +/- 1.3%). Furthermore, a direct relationship between changes in free water clearance and changes in papillary tissue, osmolality was found. Finally, the increase in urine osmolality after ADH was significantly less in vasodilated than in control kidneys. These results indicate that bradykinin can diminish the medullary osmotic gradient during water diuresis in the dog. Thus, a bradykinin-induced increase in free water clearance may be accounted for by other than an inhibition of proximal tubular sodium reabsorption.