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), intrarenal venous pressure, filtration fraction, and sodium excretion were determined sequentially before and during a 1 h infusion of isotonic saline 80 ml/kg in anesthetized dogs. The cortical fraction of renal blood flow rose during the first 20 min of infusion from an average of 70 to 77%, but returned nearly to control levels during the last 20 min of infusion because of a late 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, whereas in the last 20 min cortical blood volume had fallen nearly to control values and kidney volume was increased by 17.2%. Intrarenal resistances calculated from intrarenal pressure 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 changing continuously during saline infusion and the natriuresis probably is multifactorial.