Mechanical and Electrophysiological Effects of Some Local Anaesthetic Agents and Their Isomers on the Rat Portal Vein

Mechanical and electrophysiological effects of the DL, L and D‐forms of mepivacaine and bupivacaine and of the optically inactive compound tetracaine have been studied on the isolated rat portal vein. After the addition of the local anaesthetics to vessels in normal Krebs solution there was an initially increased spike activity accompanied by increased mechanical activity. L(+)‐mepivacaine was more potent than D(‐)‐mepivacaine in increasing the tension, but there was no significant difference between L(‐)‐and D(+)‐bupivacaine. After the initial contractile phase the tension decreased and disappeared despite continous spike activity. The relaxation appeared and proceeded faster with high than with low concentrations of local anaesthetics; the relaxations also proceeded faster in experiments with D(‐)‐mepivacaine than with L(+)‐mepivacaine. At a later stage the spike discharge was also blocked. In muscles that were contracted with K+ or noradrenaline the local anaesthetics caused a relaxation. D(‐)‐mepivacaine was more potent than L(+)‐mepivacaine, but there was still no difference between L(‐)‐ and D(+)‐bupivacaine.