Majallah-i Dānishgāh-i ̒Ulūm-i Pizishkī-i Bābul (Jan 2004)
The role of pretreatment with Dexamethasone on inhibition of acute Morphine physical dependence in rat
Abstract
Background and Objective: There is complex interaction between corticosteroids and opioid system receptors. This study was designed to investigate the interaction between the effect of Dexamethasone (DEX) and morphine in opioid physical dependence in rat. Methods: In present study, 63 male wistar rats weighing 200-250 gr were selected. Rats were made dependent by injecting cumulative doses of morphine (40-120 mg/kg/sc) twice daily for six days. For evaluation of DEX effects and involved receptors, DEX was injected 1hr prior of morphine with or without one of steroid receptors antagonists (RU 38486, selective glucocorticoid receptor antagonist and spironolactone, selective mineralocorticoid receptor antagonist). The withdrawal syndrome precipitated by injection of naloxone (2 mg/kg) was induced as an indicator of morphine dependency. These behavioral parameters (Jumping, wet-dog shake, weight loss and diarrhea) were surveyed. Additionally, plasma corticosterone (PCs) had been used as another indicator of morphine dependency. Findings: This study showed that DEX could decrease the withdrawal signs (17% weight loss 51% jumping, 28% wet-dog shake and 44% diarrhea [P<0.05]) after naloxone. Pretreatment with spironolactone and RU38486 induced variations in morphine withdrawal signs. Also, co-administration of these antagonists with DEX and morphine induced modifications in withdrawal signs. Inhibition of steroid receptors could increase of PCs and co-administration of these antagonists with DEX and morphine significantly reduced PCs compared with control groups (P<0.001). Conclusion: As the results, it could be suggested that pretreatment with DEX can decrease the level of morphine physical dependency.
