Ascorbic acid tubular reabsorption

Decreased renal tubular reabsorption of tricyclic antidepressants can be caused by ascorbic acid (40). 

Saturation and Intradermal Tests. Ascorbic acid saturation tests, based on observations that subjects with low tissue reserves excreted less of a test dose of vitamin C in the urine than subjects with adequate stores, did not distinguish between varying degrees of deficiency at the lower levels of nutrition. Relatively high plasma levels must be attained before the effect of the renal tubular reabsorption is surpassed and significant excretion occurs (see Section 5). 

Pharmacokinetics During administration of high doses of ascorbic acid, plasma ascorbic acid concentrations do not rise in proportion to the dose, because of saturable absorption and extensive renal elimination aided by saturable tubular reabsorption [3 ]. For example, when the daily dose of ascorbic acid is increased from 200 to 2500 mg (from 1.1 to 14 mmol) the mean... 

The physiology of excretion of ascorbic acid, which is a threshpld substance, has been reviewed by Smith. The mechanism of reabsorption in the renal tubules is poorly understood. Average maximum tubular reabsorption was found by Ralli and associates to be 1.77 mg. per 100 ml. of tubular filtrate per minute (see Chapter 11). 

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