DEVELOPMENTAL RENAL HEMODYNAMICS

Renal blood flow, which is lower in the immature than in the mature an imal, achieves adult values in human subjects by 1-2 years of age. The age-related increase in renal blood flow cannot be completely explain ed by increases in kidney size, since nephrogenesis is complete by 36 weeks' gestation in humans. Thus, other factors, especially changes in renal hemodynamics, are likely to be responsible for the increase in renal blood flow. The increase in renal blood flow appears to be direc tly related to the decrease in renal vascular resistance during the po stnatal period. Decreases in the effect of renal vasoconstrictors, inc reases in the effect of renal vasodilators, or a combination of the tw o, may be responsible. Many mediators of vasoconstriction have been st udied, including adenosine, catecholamines, endothelin, endogenous dig italis-like peptide, and the renin-angiotensin system. Mediators of va sodilation include endothelium-derived relaxing factor (e.g., nitric o xide), prostaglandins, atrial natriuretic peptide, dopamine, and kinin s. However, the decrease in renal vascular resistance with age is most likely related to decreases in activity of the renin-angiotensin syst em and responsiveness to catecholamines; these effects are modulated b y nitric oxide. Other mediators may also be important in determining t he age-related decrease in renal vascular resistance, but their exact roles remain to be defined.