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In 1950 Brauer and Pessotti (1) observed that the concentration of sulfobromophthalein in bile reached maximal values which were not influenced by further increments in infusion rate. In 1956 Combes, Wheeler, Childs and Bradley (2) introduced the concept of maximal biliary transport capacity for sulfobromophthalein. It is now generally held that when sulfobromophthalein is infused at a rate that exceeds the maximal biliary transport capacity, the biliary excretion of the dye remains relatively constant.The effect of the initial dosage or infusion rate of sulfobromophthalein on the various parameters measuring hepatic uptake is not so uniformly agreed upon, due in part to confusion about the meaning of the parameters themselves. These include: 1) hepatic extraction-the percentage of dye removed in one passage through the liver; 2) clearance rate-the milliliters of plasma comipletely cleared of dye in 1 minute; and 3) disappearance rate or removal rate-herein defined as the percentage of remaining dye removed each minute. Unless specified, removal rate will not be used to express the number of milligrams removed per minute.Casselman and Rappaport (3), Andrews, Maegraith and Richards (4) and Combes and associates (2) have suggested that hepatic extraction is constant or nearly constant, regardless of dosage or infusion rate. Myers (5) and Cook, Lawler, Calvin and Green (6) observed the exact converse; that is, that extraction became less efficient with increasing dose. Lavers and colleagues (7) found that variation in the initial single dose did not affect the rate of removal of sulfobromophthalein from the plasma. Again, the converse has been reported: Fauvert (8) stated that increasing the initial dose decreased the plasma disappearance rate of the dye.Wheeler and associates (9, 10) recently described the hepatic uptake of sulfobromophthalein under special circumstances in which a constant infusion of dye is in excess of the maximal biliary transport capacity. Under these circumstances a portion of plasma removal of the dye is accounted for by bile excretion; this is a constant. The remainder of the dye taken up by the liver from the plasma is stored in the hepatic cells. These authors have shown that hepatic storage is directly proportional to plasma concentration. Consequently, the higher the plasma concentration, the more milligrams of dye can be stored. Limitations were not observed for any potential maximal capacity for this removal mechanism, but it should be noted that the phenomenon is not rate limited. This description does not apply to the mechanics of removal of a single injection of dye, however, because the storage compartment is empty at the outset and, obviously, no constant proportional relationship between storage and plasma concentration would be possible.Several authors (1,(11)(12)(13) reported that sodium dehydrocholate will slow the removal of sulfobromophthalein from the plasma and will delay its excretion in the bile. Cantarow, Wirts, Snape and Miller (14) and Fauvert (8)

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