Methadone’s Effect on Hypothermia-Induced Shivering in Post Anesthetic Rat: Role of Nitric Oxide

Post anesthesia shivering which happens in some patients during recovery time after general anesthesia is followed by central hypothermia and peripheral vasoconstriction. In this study, the effect of opioidergic/nitrergic systems were determined on post anesthesia shivering in rat. Animals were cooled gently on a cold surface with indirect contact with a mixture of ice and water. Animals were treated with saline; methadone (a full opioid agonist, 10 mg/kg); naltrexone (an opioid receptor antagonist, 10 mg/kg); L-NAME (a nonselective nitric oxide synthase (NOS) inhibitor, 10 mg/kg). The core body temperature and the frequency of basal state- and post anesthetic-shivering were recorded using a stainless steel rectal probe (MLT-1403, AD Instruments®) and electromyography (EMG) electrodes connected to Animal Bio Amp (FE136, AD Instruments®) signal conditioner, respectively. Methadone administration reduced the frequency of shivering after anesthesia, while injection of naltrexone and L-NAME increased post anesthetic shivering compared to vehicle group. Co-administration of L-NAME and methadone showed a significant decrease the frequency of post anesthetic shivering. Furthermore, the temperature of shivering onset was reduced following methadone administration, which was blocked by injection of both naltrexone and/or L-NAME. To conclude, the findings of this study revealed the protective impact of methadone on post anesthesia shivering-induced with hypothermia dominated to nitrergic pathway effects in rat.