The transport of tetracyclines across the mouse ileum in vitro: the effect of cations and other agents.

The intestinal transfer of different tetracyclines dissolved in calcium- and magnesium-free Krebs bicarbonate buffer solution, pH 7.4, was studied using the everted ileum of the mouse. The rates of transfer of chlortetracycline and demethylchlortetracycline were less than those of tetracycline and oxytetracycline, the latter compounds being transferred at the same rate. Addition of calcium and magnesium to the buffer greatly reduced the transfer of tetracycline; this inhibition could be antagonized by EDTA. The presence of iron also inhibited the transfer of tetracycline. The inhibitory effect of these ions on tetracycline transfer seemed due to chelation of the drug. Glucosamine and acetylmethionine, but not acetyl glucosamine, diminished the intestinal transfer of tetracyclines. The former two agents did not influence the uptake of tissue fluids. Tetracycline was also transfered from the serous to the mucous coat in the non-everted intestinal sac of mice. The above observations suggested that the absorption of tetracyclines was not due solely to passive diffusion.