Gastrointestinal absorption of ascorbic acid in guinea pigs.

Abstract

Gastrointestinal tract of guinea pigs was recirculated in situ with ascorbic acid, and absorption rate was determined in order to discuss its feasible mechanism involved. The absorption rate of ascorbic acid from the small intestine was a little larger than that from the stomach especially in relatively lower dose, and a type of saturation kinetics was observed in both sites. Apparent Michaelis constants were 1.30 mM and 1.27 mM for stomach and small intestine respectively, indicating almost the same apparent affinity to both sites. Additional absorption experiments were carried out in the presence of three metabolic inhibitors (phlorizin, ouabain, and 2, 4-dinitrophenol), dehydroascorbic acid, and glucose. Phlorizin or glucose was considered to exert a competitively inhibiting effect on the small intestinal absorption of ascorbic acid, while the stomach absorption was affected neither remarkably nor competitively by almost all of the adjuvants. A difference in those inhibitoty effects as well as the properities of drug moiety is fully suggestive of that in absorption mechanism between the two sites. It may be simultaneously implied, from the blood level immediately after 1 hr tests of recirculation and its curve following i. v. administration of ascorbic acid, that the absorbed drug will be rapidly distributed in the animal tissue cells.