Endogenous bradykinin regulates renal function in the newborn rabbit

The developmental changes in the activity of the renal kallikrein-kinin 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 receptor antagonist HOE-140 was investigated in newborn rabbits. Effective blockade of bradykinin effect by HOE-140 was demonstrated in 10 rabbits. In 10 additional animals the subcutaneous injection of 300 micrograms/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, indicating 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 regulatory role for the renal KKS in the immature kidney under basal conditions. By inducing predominant efferent arteriolar vasodilation, the KKS appears to play a key role in regulating the neonatal glomerular microcirculation. This is in sharp contrast with the mature kidney, where the KKS predominantly acts on tubular function as a diuretic-natriuretic factor.