Hemodynamic adaptation to reduced renal mass in early postnatal development.

Radioactive microspheres, clearance methodology, and glomerular counting techniques were used to compare hemodynamic changes resulting from uninephrectomy at birth with those of sham-operated guinea pigs 8-13 days of age and 18-24 days old. Left renal blood flow doubled from 10-20 days of age, and was approximately 65% higher in animals with reduced renal mass. Cardiac output also doubled from 10-20 days of age but was not significantly affected by uninephrectomy whereas mean arterial blood pressure rose with normal or compensatory renal growth. There was a progressive fall in renal vascular resistance that paralleled the drop in total peripheral resistance during normal growth, but the fraction of cardiac output supplying the remaining kidney of renoprival guinea pigs rose significantly from 7% at 10 days to 11% at 20 days of age. Whole kidney filtration fraction averaged 0.25-0.29 for all groups. There was no change in cortical blood flow distribution with age or after uninephrectomy: 50, 30, and 20% supplied outer, middle, and inner thirds, respectively. Glomerular perfusion rate increased proportionately in all cortical levels during normal or compensatory renal growth, and was higher in outer and inner cortical thirds than in the middle cortex. It is concluded that systemic and intrarenal hemodynamic responses to uninephrectomy at birth are similar to the pattern of normal maturation. Reduction in renal mass and normal somatic growth provide additive stimuli resulting in maintenance of homeostasis.