Effect of long-term glucocorticoid administration on nondepolarizing muscle relaxants-induced neuromuscular blockade in rat diaphragma

Objective To evaluate the effect of long-term glucocorticoid administration on nondepolarizing muscle relaxants-induced neuromuscular blockade in rat diaphragma in vitro.Methods Forty adult male SpragueDawley rats,aged 8 weeks,weighing 180-220 g,were randomized into 2 groups (n =20 each):control group (group C) and dexamethasone group (group D).In group D,dexamethasone 0.6 mg/kg was injected intraperitoneally once a day for 14 consecutive days,while the equal volume of normal saline was injected instead of dexamethasone in group C.The left phrenic nerve-hemidiaphragm was removed at 24 h after the last injection to evaluate the effect of d-tubocurarine.Different concentrations (0-10 μmol/L) of d-tubocurarine were added.The d-tubocurarine concentration-effect curve was drawn.The half inhibitory concentration and 95 ％ confidence interval of d-tubocurarine were calculated.Right diaphragma was removed for determination of the expression of embryonic nicotinic acetylcholine receptor (nAChRγ) mRNA and adult nicotinic acetylcholine receptor (nAChRe) mRNA by RTPCR.Results Compared with group C,the concentration-effect curve was shifted to the right,the half inhibitory concentration was significantly increased,and the expression of nAChRγ mRNA and nAChRe mRNA was up-regulated in group D (P ＜ 0.05).Conclusion Long-term glucocorticoid administration can weaken nondepolarizing muscle relaxants-induced neuromuscular blockade in rat diaphragma in vitro,and up-regulation of nAChR mRNA expression may be involved in the mechanism. Key words: Glucocorticoids ;  Neuromuscular nondepolarizingagents ;  Neuromuscular blockade