RENAL TUBULAR SECRETION AND REABSORPTION OF ORGANIC BASES IN THE DOG*

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Abstract
Under conditions in which urine pH and volume are rigidly controlled, organic base excretion in the dog shows competitive inhibition, a phenomenon consistent with tubular secretion by active transport. Since mutual inhibition is demonstrable for both amines and onium compounds, it is inferred that both types are secreted as the charged particle. The pH dependence of amine excretion is attributable to non-ionic diffusion in a reabsorp-tive direction. Diffusion from the peritubular space into the tubular fluid cannot be rigidly excluded, but if it occurs it is limited in amount due to the relatively slow approach to diffusion equilibrium. The final concentration of organic base in the voided urine depends on multiple factors whose relative importance varies with pH and other experimental conditions.