Résumé
BACKGROUND: To elucidate the mechanism of interaction between depolarizing and nondepolarizing muscle relaxants, train-of-four (TOF) fade during onset of neuromuscular blockade of d-tubocurarine (dTC) with or without decamethonium (C10) was evaluated in a rat phrenic nerve hemidiaphragm preparation. METHODS: Phrenic nerve hemidiaphragm preparations from 250~300 g Sprague Dawley rats (n=20) were suspended in a Krebs solution bubbled with 5% CO2 in O2 at 32oC. Phrenic nerves were stimulated with supramaximal stimuli of 0.2 ms duration at 0.15 Hz single twitch and 2 Hz TOF by a Grass S88 stimulator and the contractions of the hemidiaphragm were detected by a Grass FT03 force transducer then recorded. Estimation of ED50 for the dose response data were performed by a linear regression. The statistical significance of the results was determined by Wilcoxon Rank Sum test. p<0.05 was considered significant. RESULTS: Mean ED50 values of dTC and C10 calculated from the dose response relations were 7.76 microgram/ml and 0.65 microgram/ml respectively. Compared to adminstration of 2xED50 of dTC alone, TOF ratios at 75% and 50% of twitch height were markedly decreased by combination of ED50 of C10 and ED50 of dTC with statistic significance (67 +/- 1.9% vs. 46 +/- 3.1% and 36 +/- 2.5% vs. 7 +/- 2.5%). Conclusion: If fade in response to TOF stimulation represents a prejunctional effect, the results from this study suggests that the presynaptic action of C10 has some role in the mechanism of the interaction between dTC and C10 in the rat.