Nitric oxide modulates glomerular filtration and renal blood flow of the newborn rabbit

The current study was performed in 17 anesthetized and mechanically ventilated newborn rabbits to investigate the role of nitric oxide (NO) in the regulation of basal renal function of the immature kidney. Renal blood flow and glomerular filtration rate were determined by the clearance of p-aminohippuric acid and inulin, respectively. In 9 newborn rabbits (group 1), L-NAME, a NO synthesis inhibitor, significantly increased the renal vascular resistance by 31 +/- 9% and decreased the renal blood flow by 20 +/- 6%. The fraction of filtration significantly increased by 8 +/- 5% despite a delayed decline in glomerular filtration rate by 13 +/- 5%. Mean arterial pressure and heart rate were not altered. In 8 additional newborn rabbits (group 2), L-arginine, the physiological precursor of NO synthesis, partially reversed the renal hemodynamic changes induced by L-NAME. The present results demonstrate that the decrease in NO production induced by L-NAME (1) significantly affects the renal microcirculation of the immature newborn rabbit kidney and (2) predominantly increases the postglomerular renal vascular resistance. Endogenous NO thus appears to play a major role in maintaining the basal perfusion of the immature kidney.