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 (nAChRε)
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 nAChRε
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.