Dexamethasone reduces morphine-induced Straub reaction in mice

This study examined the effect of dexamethasone on morphine-induced straub reaction in mice. When morphine was administered in doses of 7.5, 15 and 30 mg kg(-1) intraperitoneally, a dose-dependent straub reaction was produced. Dexamethasone per-se (0.1-10 mg kg(-1) i.p.) did not modify the tail of control mice. Pre-treatment with dexamethasone 120 min before morphine injection caused a dose-dependent reduction of straub reaction. Cycloheximide (15 mg kg(-1) i.p.) administered 2 h before morphine did not change morphine-induced straub reaction, but was able to prevent the effects of dexamethasone on morphine-induced straub reaction. The glucocorticoid receptor antagonist RU-38486 (15 mg kg(-1) i.p.) did not affect morphine-induced straub reaction, whereas it was able to block the effects of dexamethasone on morphine-induced straub reaction. Results of this study indicate that dexamethasone reduced morphine-mediated straub reaction in mice, indicating a further important functional interaction between dexamethasone and the opioid system. The ability of cycloheximide and RU-38486 to block dexamethasone's effects indicates that the steroid's interference with morphine-mediated straub reaction involves a protein-synthesis-dependent mechanism via glucocorticoid receptors.