Biomedical Research

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.

Author(s): Shigeki Fujiwara, Akiko Noguchi, Masanori Tsukamoto, Shinichi Ito, Uno Imaizumi, Yoshinari Morimoto, Kazu-ichi Yoshida, Takeshi Yokoyama
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