THE MECHANISM OF THE EXCRETION OF VITAMIN C BY THE HUMAN KIDNEY 1

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Abstract
Simultaneous vit. C and insulin clearances show that vit. C is excreted by filtration and active tubular reabsorption. The reabsorptive mechanism for vit. C appears to be limited by a maximal rate, so that when the vit. is presented to the tubules by the glomerular filtrate at a rate exceeding this maximum, the excess is excreted in the urine. The maximal rate of reabsorption in 3 individuals averaged 2.16 ragm. per min. (or 1.77 mgm. per 100 cc. of glomerular filtrate). The excretion of vit. C in a given individual will be detd. by the plasma level, the rate of glomerular filtration, and the maximal rate of tubular reabsorption. At low plasma levels the vit. C clearance reaches a minimal and constant value. Simultaneous vit. C, inulin and glucose clearances show that vit. C is not reabsorbed by the same mechanism as glucose.