Identification of metabolites of sulfobromophthalein.

Sulfobromophthalein (BSP) is normally cleared from the blood by the liver and excreted into the bile. Brauer, Krebs and Pessotti (1) originally reported that part of the pigment appearing in dog bile was chromatographically different from the injected dye. Our studies using differenlt chromatographic techniques indicate that in man the bulk of the recovered pigments (65 to 75 per cent, according to estimates based on their absorption at 575 nu) consists of two metabolites. Similar metabolites are normally found in the urine and trace amounts also appear in the serum. The absorption spectra in the visible range and the indicator characteristics of BSP and the metabolic products were indistinguishable (2). The liver apparently is capable of producing the metabolites, since they have beeni demonstrated in bile from preparations of isolated rat liver perfused with BSP (3, 4). Variations in the concentration of BSP metabolites in serum and urine of patients witlh liver disease are reported elsewhere (5). Since the chemical difference between the free dye and its metabolites elucidates in part the mechanismii of hepatic function involved in BSP clearance, characterization of this structural difference has received considerable attention. BSP is a derivative of phenolphthalein, therefore both compounds cotuld be excreted by the sanme patlhway, that is, by conjugation witlh glucuronic acid (6). This mechanism for BSP clearance appears unlikely since the metabolites were stable to hydrolysis with 8-glucuronidase (4, 7), with dilute acid and with dilute base, and gave a negative Dische reaction for uronlic acid (4). Furthermiiore, both of the major metabolites in human bile were associated with ninhydrin-positive substances,