Renal tubular transport of paracetamol and its conjugates in the dog.

1 The renal tubular transport of paracetamol and its conjugates was investigated with renal clearance and stop flow studies in the dog. Paracetamol is sparingly bound to plasma proteins and therefore undergoes glomerular filtration. It is reabosrbed in the renal tubules by simple diffusion. 2 The conjugates of paracetamol, the sulphate and the glucuronide, both undergo glomerular filtration being weakly protein bound. At low concentrations in plasma both compounds are secreted by an active transport process. At higher concentrations both compounds are reabsorbed. Clearances are not dependent on urinary pH or flow rate. It is concluded that reabsorption is not a passive process but that there is an active bidirectional transport of the conjugates. 3 Net tubular secretion of the sulphate, but not the glucuronide, conjugate was inhibited by the administration of probenecid.