CHARACTERISTICS OF CEPHALEXIN TRANSPORT ACROSS ISOLATED RABBIT ILEUM

The purpose of this study was to examine the total transepithelial (tr anscellular, paracellular and carrier-mediated) transport of cephalexi n (CFX) across isolated rabbit ileum. This epithelium was mounted in G rass diffusion cells to separate the mucosal and serosal compartments. The tissue was immersed on each side into a Ringer's solution or a PB S buffer solution at 37 degrees C and oxygenated (O-2/CO2 in 95/5, v/v ). The concentration dependence of CFX transport was examined over a c oncentration range of 0.1-5 mM and showed a Michaelis-Menten kinetics. The inhibition of CFX transport was 97 +/- 1% at 4 degrees C and 30 a nd 61% with metabolic inhibitors such as sodium azide (1 mM) and 2.4 d initrophenol (0.1 mM) respectively. The CFX transepithelial flux was g reater at pH 6 (11.42 +/- 2.24) than at pH 7-7.4 (5.0 +/- 1.03) in nmo l/h per cm(2). Without a pH gradient at pH 7.4 this effect was inhibit ed by FCCP and nigericin. At pH 7.4, amiloride did not affect CFX tran sport but ouabaine significantly affected the CFX flux with an inhibit ion of 90%. No paracellular diffusion was observed in the presence of D-glucose (25 mM). The mucosal to serosal flux of 0.1 mM of CFX was si gnificantly inhibited by 1 mM of gly-pro. Similarly, cephradine (2 mM) inhibited 0.2 mM of CFX by 23% and amoxicilline (5 mM) reduced the tr ansport by 56%. L-phenylalanine did not affect the transport of 0.5 mM of CFX. The transport of CFX through rabbit ileum followed Michaelis- Menten kinetics at lower concentrations, was pH-dependent, energy-depe ndent, Na+-independent and occurred across the intestinal mucosa throu gh a transcellular route via dipeptide carrier system(s). (C) 1997 Els evier Science B.V.