Purpose: To evaluate in vitro lidocaine and racemic bupivacaine effects in neuromuscular transmission and in neuromuscular blockade produced by rocuronium.
Methods: Rats were distributed in 5 groups (n = 5) in agreement with the studied drugs: lidocaine, racemic bupivacaine, rocuronium, separately (Groups I, II, III); rocuronium in preparations exposed to local anesthetics (Groups IV, V). The concentrations used were: 20 microg/mL, 5 microg/mL and 4 microg/mL, for lidocaine, bupivacaine and rocuronium, respectively. It was evaluated: 1) amplitude of diaphragm muscle response to indirect stimulation, before and 60 minutes after separately addition of lidocaine, racemic bupivacaine and rocuronium and the association of local anesthetics - rocuronium; 2) membrane potentials (MP) and miniature end-plate potentials (MEPP).
Results: Lidocaine and bupivacaine separately didn't alter the amplitude of muscle response and MP. In preparations previously exposed to lidocaine and racemic bupivacaine, the rocuronium blockade was significantly larger (90.10 +/- 9.15% and 100%, respectively), in relation to the produced by rocuronium separately (73.12 +/- 9.89%). Lidocaine caused an increase in the frequency of MEPP, being followed by blockade; racemic bupivacaine produced decrease being followed by blockade.
Conclusions: Local anesthetics potentiated the blockade caused by rocuronium. The alterations of MEPP identify presynaptic action.