Urinary excretion of dye in dogs infused with BSP or its glutathione conjugate.

Renal clearance of BSP compounds was investigated in dogs during infusion of sulfobromophthalein (BSP) or its glutathione conjugate (BSP-GSH). Conjugated BSP compounds are more readily excreted into urine than unconjugated BSP. Dye clearance into urine was much less than simultaneously measured inulin clearance. This suggests that protein binding of BSP compounds significantly retards the glomerular filtration of the dye. BSP was found to bind more avidly to albumin than BSP-GSH. The ratio of dye clearance to inulin clearance remained relatively constant over a broad range of plasma concentrations of dye. The data support but do not prove glomerular filtration of non-protein-bound dye as the major mechanism accounting of urinary elimination of BSP compounds in the dog.