Inhibitory Effects of Angiotensin-Converting Enzyme Inhibitors on Cefroxadine Uptake by Rabbit Small Intestinal Brush Border Membrane Vesicles

Abstract

Effects of angiotensin-converting enzyme (ACE) inhibitors, captopril, enalapril maleate and quinapril, on the uptake of aminocephalosporin antibiotic, cefroxadine, by rabbit small intestinal brush border membrane vesicles were examined. These ACE inhibitors significantly inhibited the uptake of cefroxadine, which is transported by H⁺/dipeptide transporter in the membrane, in the order of captopril<enalapril<quinapril in the presence of an inward H⁺ gradient. Inhibitory effect of quinapril was more marked than that of aminocephalosporin cepharadine, while in the absence of an inward H⁺ gradient inhibition by these ACE inhibitors was much less. Dixon plot analysis showed that the inhibition by enalapril and quinapril in the presence of an inward H⁺ gradient occurred in a competitive manner and estimated inhibition constants of these two drugs to be 5.3 mM and 0.46 mM, respectively. These results suggested the strong affinity of these ACE inhibitors, especially quinapril, on the H⁺/dipeptide transporter.