BACKGROUND: The effects of local and inhalation anesthesia on the contraction of the tracheal smooth muscle have been reported. However, when inhalation and local anesthesia are administered simultaneously, their effects on the contraction of the airway smooth muscle are not well known. Therefore, this study evaluated the effects of lidocaine, bupivacaine, with or without enflurane, on the histamine induced tracheal smooth muscle contraction in guinea pigs.

METHODS: Isolated tracheal rings of guinea pigs were suspended in Krebs solution. The contractions were recorded isometrically using a transducer. A contraction was induced by histamine (10^-5 M). Enflurane (1 MAC) was administered for 15 min after administering the histamine. The cumulative dose responses of the lidocaine and bupivacaine (10^-8 M, 10^-7 M, 10^-6 M, 10^-5 M, 10^-4 M, and 10^-3 M), enflurane-lidocaine and enflurane-bupivacaine groups were checked.

RESULTS: The contraction by histamine were inhibited by lidocaine (10^-4 M and 10^-3 M) and bupivacaine (10^-5 M, 10^-4 M and 10^-3 M). In addition, the contractions were inhibited more significantly in the bupivacaine group (10^-7 M, 10^-6 M, 10^-5 M, 10^-4 M and 10^-3 M) after administering enflurane.

CONCLUSIONS: Lidocaine and bupivacaine inhibited the contractions induced by histamine. The contractions by bupivacaine were further inhibited after administering enflurane.