IN A PREVIOUS balance of bilirubin from this laboratory, retention of bilirubin occurred in extravascular tissue spaces.1 When 8 mg of bilirubin/100 gm of mature rat was infused during a 60-minute interval, the animals excreted 40%. Of the retained bilirubin, 25% was accounted for by direct analysis in the plasma and 7% in adipose tissue. The remaining 68% of the retained bilirubin was presumed to be in extravascular tissue spaces which were non-adipose. This "residual" bilirubin was derived by arithmetic difference from the balance rather than from direct analysis. A more direct measurement of the residual bilirubin and particularly its intracellular distribution was desired.
One obvious location for significant quantities of infused bilirubin is in the liver. A number of investigations have demonstrated the rapidity with which the liver can remove bilirubin from the circulating plasma and excrete it in bile as its conjugated derivatives,2-4 Schmid and co-workers