Ovariohysterectomy in the rat: a model of surgical pain for evaluation of pre-emptive analgesia?

Ovariohysterectomy in the rat led to the induction of abdominal postures an d referred mechanical allodynia in the hind paws. The latter was differenti ated into static and dynamic subtypes. The abdominal postures were present up to 4-5 h, whilst the two types of allodynia lasted for at least 2 days. A single administration of morphine 30 min before surgery dose-dependently (0.1-3 mg/kg, s.c.) blocked the development of abdominal postures and the t wo types of mechanical allodynia. The highest dose of morphine almost compl etely blocked these responses. The duration of action of 3 mg/kg morphine w as short and similar (1,5-2 h) when administered either before or after sur gery. However, multiple administrations of morphine (0.5 h before, and 0.5 and 2 h after surgery) blocked the development of abdominal postures and bo th allodynias for up to 2 days. In contrast, administration of three doses of morphine (3 mg/kg) in a similar dosing regime but starting 24 h after su rgery, only blocked the two types of allodynia for 4 h. These data indicate the importance of blocking the induction phase of surgical pain and suppor t the concept of pre-emptive analgesia. It is suggested that the ovariohyst erectomy model should prove to be useful for studying mechanisms and design ing novel therapeutic strategies for the treatment of post-operative pain. (C) 2000 International Association for the Study of Pain. Published by Else vier Science B.V. All rights reserved.