ENDOGENOUS BRADYKININ REGULATES RENAL-FUNCTION IN THE NEWBORN RABBIT

The developmental changes in the activity of the renal kallikrein-kini n system (KKS) are related to the hemodynamic changes occurring in the neonatal kidney. In order to clarify the functional importance of the renal KKS in the developing kidney, the effect of the bradykinin B2 r eceptor antagonist HOE-140 was investigated in newborn rabbits. Effect ive blockade of bradykinin effect by HOE-140 was demonstrated in 10 ra bbits. In 10 additional animals the subcutaneous injection of 300 mu g /kg HOE-140 resulted in an increase in renal vascular resistance with a consequent decrease in renal blood flow. Glomerular filtration rate did not change significantly, while the filtration fraction rose, indi cating preferential efferent arteriolar constriction. Urine flow rate increased as well as the fractional excretion of potassium. No change in sodium excretion was observed. The present data suggest a regulator y role for the renal KKS in the immature kidney under basal conditions . By inducing predominant efferent arteriolar vasodilation, the KKS ap pears to play a key role in regulating the neonatal glomerular microci rculation. This is in sharp contrast with the mature kidney, where the KKS predominantly acts on tubular function as a diuretic-natriuretic factor.