Physico-chemical modification of lidocaine uptake in rat lung tissue

The uptake of lidocaine, methyllidocaine, bupivacaine, etidocaine was studied in rat lung slices at different pH-values. The accumulation of the quaternary analogue, methyllidocaine, was not changed in the pH interval 7.0--8.0. The uptake of the three other substances was about 3--4 times lower at pH 7.0 than at pH 8.0. The rank order of distribution at a fixed cation/base ratio was bupivacaine greater than etidocaine greater than lidocaine. Interactions between lidocaine and other substances were studied in lung slices and in isolated perfused lungs. Bupivacaine and nortriptyline counteracted the accumulation of 14C-lidocaine in lung slices in a dose-dependent manner. Nortriptyline was more effective than bupivacaine. In isolated perfused lung, bolus injections of nortriptyline and lidocaine rapidly displaced 14C-lidocaine from the tissue. In this study we suggest that the base form of local anaesthetics accumulate in the lung tissue, while the cationic form binds to accessible binding sites in the cell membranes.