Abstract
Background & Objectives: Several types of receptors are found at neuromuscular presynaptic side. Of these receptors, muscarinic facilitatory M1 and inhibitory M2 receptors regulate the fine-tuning actions of acetylcholine on neuronal firing. The primary objectives of this study were to find the changes of variables obtained during neuromuscular blockade by rocuronium after blocking neuromuscular presynaptic muscarinic M2 receptors. In this study, we investigated whether methoctramine contributes to tetanic fade triggered the stimulation of 50 Hz tetanic stimulation after small dose of rocuronium. Materials & Methods: A total of 30 phrenic nerve-hemidiaphragm samples were obtained at Sprague-Dawley rats and each sample was randomly allocated to the control group, MET1, or MET10 group (methoctramine administered at 1 μM, 10 μM respectively). The study protocol (Protocol No. 2012-14-255, 2015-14-076) was approved beforehand by the Ethics Committee of the Laboratory of Animal Research of our institute. While the samples were stimulated by TOF with 20sec interval, 50 Hz 5sec tetanic stimulation was administered at initial, 20min after administration of rocuronium loading dose, and 30min after administration of methoctramine, and obtained initial (A), last (B) tension and its ratio (R). Results: When comparing the R values, which is the ratio of B over A, there were significant changes before and after administration of methoctramine in MET10 group, and the value after administration of methoctramine in MET10 was significantly lower than other groups. The amount of changes in R value were larger in MET10 group comparing with other groups. Conclusion: Overall function of neuromuscular presynaptic mAChRs is to preserve or save the presynaptic function on various neuronal stimulation and this function might be disrupted by interfering the balance between these receptors. Blockade of M2 mAChR may influences to the value obtained at tetanic stimulation for monitoring neuromuscular blockade made by rocuronium.
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