Absorption and Excretion of Drugs. XXXIII. The Correlation between the Absorption of Barbituric Acid Derivatives from the Rat Small Intestine and Their Binding to the Mucosa

Abstract

In order to examine the fundamental problems concerning the contribution of the binding to the mucosa in the absorption of barbituric acid derivatives from the rat small intestine, some in situ and in vitro experiments were carried out. It was clarified that the accumulation in the small intestine was negligible during the in situ continuous perfusion, and therefore the absorption rate constants computed from the amount decreased in the perfusion solution express almost quantitatively the penetration into the vascular system. The degree of binding to the mucosa determined in vitro was correlated to the absorption characteristics. The importance of the binding process in the absorption was also confirmed by in vitro uptake experiments. The uptake was classified into two processes ; the adsorption on the mucosal surface and the accumulation in the tissue. Of these two processes, the adsorption was ascertained as a determining step in the entire absorption process from the rat small intestine.