Plasma Clearance of Rose Bengal (Tetraiodotetrabromfluorescein)

Abstract

Disappearance of Rose Bengal from the plasma after a single intravenous injection of the dye may be used for the estimation of plasma clearance of this dye. The plasma clearance has dimensions of milliliters per minute, and appears to be independent of plasma concentration when doses below 60-120 mg of dye are used. The single injection clearance is essentially equal to that obtained by constant infusion methods in the early part of the infusion. This supports the idea that the single injection clearance is a valid measure of the plasma clearance. The single injection clearance is depressed when large quantities of dye are given at one time, and the constant infusion clearance becomes depressed in the course of a prolonged infusion. This is interpreted to indicate that the limiting factor in dye elimination has become the capacity of the liver rather than the rate at which dye is delivered to the liver. It is further concluded that the capacity of the excretory mechanism is diminished as dye is eliminated, i.e., that there is a depletable reservoir of capacity for dye excretion. It is shown that Rose Bengal extraction cannot be demonstrated in the areas drained by the femoral and jugular veins. It is further shown that the hepatic blood flow estimated by dividing the blood clearance of Rose Bengal by the hepatic extraction ratio of the dye is smaller than the estimated hepatic blood flow determined by others using the same method with BSP. It is concluded that Rose Bengal has a smaller ratio of extrahepatic to hepatic clearance than does BSP. Evidence is presented to indicate that in prolonged infusions Rose Bengal and BSP may have an extravascular distribution. The errors involved in the estimation of hepatic blood flow by infusion techniques if such extravascular distribution exists are indicated.