بررسي تغيير پاسخ دهي به اثر ضد دردي مرفين و تحمل به مرفين بعد از حذف تخمدان هاي موش صحرايي ماده

The Difference of Analgesic Effect and Tolerance to Morphine between Ovariectomized and Intact Female Rats

Background: Estrogens have numerous non-reproductive neurobiological effects on the brain through the nuclear hormone receptor activities of intracellular ERa and ER(3. Some of these receptors involve in pain modulation and conduction. In the present study, the morphine tolerance and its analgesic effect in ovariec¬tomized (OVX) rats was investigatedy. Methods: Fourty female rats were divided into 4 groups: Sham, OVX, Sham-Tolerance, and OVX- Tolerance. Eight weeks after surgery, morphine tolerance was induced by daily injection of 20 mg/kg morphine during 4 consecutive days in animals of groups 3 and 4. Animals of groups 1 and 2 were simultaneously treated with 1 ml/kg saline, respectively. Hotplate test was carried out in 5th day as a base record, then the animals received 5 mg/kg morphine and antinociceptive effect was evaluated every 10 minutes. Findings: The reaction times after morphine (5 mg/kg) injection was higher than base time in sham and OVX groups but there was not difference in OVX-Tolerance and Sham-Tolerance. However the reaction time after injection of morphine (5 mg/kg) in sham group was higher than OVX group and there was not difference between Sham- Tolerance and OVX-Tolerance. Conclusion: The result showed that repeated administration of morphine can lead to tolerance. How¬ever there were not difference between tolerance in the presence and absence of female gonadal hor¬mones. Keywords: Rat, Ovariectomized, Pain, Tolerance.