Aim: In our previous study, we demonstrated that the vasoconstrictive action of lidocaine occurs at a concentration of 10-4 mol/L. Furthermore, we found that lidocaine enhanced contractile responses produced by low concentrations of adrenaline (10-8-10-7 mol/L). In this study, the responses of isolated rat thoracic aorta preparations to local anaesthetic solutions containing either prilocaine or mepivacaine were examined in the presence of adrenaline or noradrenaline.
Methods: We isolated thoracic aorta from Wister rats. The arteries were cut into ~3 mm long rings that were stretched by a pair of hooks in an organ bath filled with Krebs-Henseleit solution. After 1 μg/ml lipopolysaccharide treatment, vasoconstrictors (either adrenaline or noradrenaline) were applied in a cumulative manner between concentrations of 10-9–10-5 mol/L of either prilocaine or mepivacaine (10-4 mol/L). Changes in isometric vasocontractions were continuously recorded with an amplifier system using the PCD-30A computer system.
Results: The contractile response to both prilocaine and mepivacaine significantly decreased at low concentrations of adrenaline (10-8-10-7 mol/L). The contractile response to mepivacaine also significantly decreased at low concentrations of adrenaline (10-9-10-8 mol/L). In contrast, with the exception of prilocaine at a low concentration of adrenaline (10-8 mol/L), neither prilocaine nor mepivacaine significantly decreased the contractile responses. In a model of blood vessel inflammation under 6 h lipopolysaccharide treatment, prilocaine and mepivacaine enhanced contractile responses produced by 10-9-10-7 mol/L noradrenaline.
Conclusion: Noradrenaline should be administered when injecting inflamed tissues with prilocaine or mepivacaine.