The effect of adrenaline or noradrenaline with or without lidocaine on the contractile response of lipopolysaccharide-treated rat thoracic aortas

The analgesic effect of a local anesthetic is often insufficient in acutely inflamed tissues, due to the reduced pH and/or vasodilation. Thus, vasoconstrictors (adrenaline or noradrenaline) are often used to contain the anesthetic and prolong the analgesia, although there are minimal data regarding their effects in inflamed tissues. Therefore, we prepared a model of blood vessel inflammation (using lipopolysaccharide), and investigated the contractile effects of adrenaline or noradrenaline with and without lidocaine. Wistar rats’ thoracic aortas were cut into 3-mm-thick rings, which were stretched using a pair of hooks in an organ bath (Krebs-Henseleit solution, 37°C, pH=7.4). After lipopolysaccharide exposure (1 μg/mL), adrenaline or noradrenaline was applied in successive cumulative doses (10-9 to 10-5 M) with or without lidocaine (10-4 M), and the isometric vasocontractions were recorded. The lipopolysaccharide treatment attenuated the vasocontractions that were induced by adrenaline or noradrenaline with lidocaine in a time-dependent manner. Despite its vasodilation properties, lidocaine enhanced the contractile responses that were produced by low concentrations of adrenaline (10-8 to 10-7 M), which indicates that a sufficient analgesic effect depends on the concentration of lidocaine and adrenaline. Therefore, adrenaline should be used when injecting inflamed tissues with lidocaine.