Reabsorption and secretion of ι-malic acid in kidney proximal tubule

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Abstract
The ι-malic excretion pattern was studied in the dog using the "stop flow" method. During ι-malic and fumaric infusions, a net reabsorption of ι-malic acid was seen only in the proximal tubule. This reabsorption occurred against a massive concentration gradient and, therefore, was justifiably termed active reabsorption. Infusion of succinate produced a net secretion of ι-malic. This was also confined to the proximal tubule. The secretion, however, occurred in the direction of the concentration gradient and, therefore, was probably a diffusion phenomenon. The secretion could be inhibited by malonate. It was concluded that the renal transports of ι-malic acid are intimately related to the operation of the tricarboxylic acid cycle.