Renal Medullary Red Cell and Plasma Flow as Studied with Labelled Indicators and Internal Detection

Regional renal medullary red cell and plasma flow has been investigated on 8 dogs using 32‐P labelled red cells and plasma and detection with small needle‐shaped semiconductor detectors put into the parenchyma. The transit times were determined by dividing the area with the height of the indicator‐dilution curves obtained after slug injections of alternatively labelled red cells and labelled plasma into the renal artery. Regional red cell volume was obtained from intrarenal equilibrium activity. The plasma volumes relative to the red cell volumes was determined by comparing the areas of the two indicator‐dilution curves. Whole blood flow was then estimated at 2 ml/min and g tissue in the outer zone continuously decreasing to values around 0.5 ml/rnin and g tissue in the inner parts of the inner zone. The hematocrit in vasa recta blood (denoting the ratio between the flow of red cells to the flow of whole blood) was in the outer zone 85% of that in arterial blood, successively decreasing to about 50% in the inner parts of the renal medulla.