Sequential changes in intrarenal hemodynamics during saline infusion in the dog

Intrarenal blood flow and volume (indicator-dilution technique), kidney volume (mercury-in-rubber resistance gage), intr-renal venous pressure, filtration fraction, and sodium excretion were determined dequentially before and during a l-h infusion of isotonicsaline 80 ml/kg in anesthetized dogs. The cortical fraction of renal blood flow roseduring the first 20 min of infusion from an average of 70 to 77%, butreturned nearly to control levels during the last 20 min of infusion because ofa low rise in noncortical flow. During the first 20 min a 23% increase in cortical blood volume accounted for one-third of the 8.5% increase in kidney volume, whereasin the last 20 min cortical blood volume had fallen nearly to control values and kidneyvolume was increased by 17.2%. Intrarenal resistances calculated from intrarenalpressure and flow indicated persistent cortical prevenous dilatation, progressive cortical venous constriction, and only a slight late reduction in noncortical resistance.These data indicate that hemodynamics are shanging continuously during saline infusion and the natriuresis probably is multifactorial.