Intrarenal Blood Flow Distribution (IRBF) in the Puppy Using Xenon Washout and Microspheres

Abstract

Total renal blood flow measured by the 133Xenon washout (Xe) rose from 1.5 ml/g/min at 6 wks. to 3.5 at 16 wks. of age in 30 canine puppies.IRBF analyzed from the Xe curve showed Component I (CI) increased from 1.7 ml/g/min at 6 wks. to 4.6 at 16 wks. and Component II (CII) increased from 0.9 at 6 wks. to 1.1 at 16 wks. The ratio CII/CI was 0.55 at 6 wks. and fell to 0.25 at 16 wks. (p<0.01). The low cortical flow was also demonstrated by 169Yb microsphere method. Anatomical vascular development using silicone rubber further showed in increase in cortical size with age. Cardiac output measured by indocyanine green in 8anesthetized puppies over an age range of 6-16 wks. remained at 90 ml/kg/min while RBF in ml/kg/min increased. The relatively low cortical flow at 6 wks. was associated with a PAH extraction ratio (EPAH) of 0.44 and filtration fraction (FF) of 0.40. EPAH increased to 0.75 at 12 wks. and FF decreased to 0.24 at 16 wks. These studies directly demonstrate for the first time underperfusion of the young puppy renal cortex as compared to the medulla. Renal functional maturation is accomplished in the canine by an increase in cortical blood flow during growth.