Renal handling of 2,4-D by the dogfish shark (Squalus acanthias)

1. The renal clearance of 2,4-dichlorophenoxyacetate (2,4-D) was studied in the dogfish shark, Squalus acanthias. 2. The clearance of total 2,4-D was more than 25 times greater than the glomerular filtration rate, which indicated that 2,4-D was secreted by the kidney. 3. The secretion of total 2,4-D was decreased by bromocresol green, an inhibitor of organic anion secretion, which also produced a concurrent decrease in the glomerular filtration rate. 4. As previously determined, 2,4-D was eliminated in the urine as the taurine conjugate (approximately equal to 95% of the excretion products). The plasma of the dogfish shark, however, contained primarily unconjugated 2,4-D (approximately equal to 90%) and only a minor amount of the taurine conjugate (approximately equal to 5%). The limited amount of the taurine conjugate in the plasma cannot account for its urinary excretion. Apparently 2,4-D is transported into the renal tubular cell, after which 2,4-D is conjugated with taurine before elimination into the urine.