Behavioural effects of laparotomy and analgesic effects of ketoprofen and carprofen in rats

Rat behaviour was studied to develop a reliable method of determining the severity and duration of post-laparotomy pain, and to assess analgesic effects of ketoprofen or carprofen. Behaviour was studied in groups of ten animals 1 h following subcutaneous (s/c) saline (0.2 ml/100 g), ketoprofen or carprofen (5, 10 or 15 mg/kg) given either alone, or prior to surgery. The frequency of over 150 individual behavioural acts was calculated during the first post-treatment hour, the hour immediately prior to darkness, and the first 15 min of each of 5 subsequent hours. Discriminant analysis and analysis of variance isolated several easily recognizable behaviours which were markedly altered in frequency by surgery. These were unaffected by drug administration alone and were mainly transient, easily quantifiable activities; ‘cat-like’ back arching, horizontal stretching followed by abdominal writhing and twitching while inactive. Reductions in the frequency of these behaviours following surgery with analgesic treatment supported the hypothesis that they reflected post-operative pain. Ketoprofen and carprofen were equipotent and no dose related effects were apparent. Analgesic activity lasted between 4 and 5 h with the 5 mg/kg dosage, this being estimated from the duration of overall and specific behaviour differences between saline and drug treated animals. The data provided substantial evidence as to the usefulness of behavioural criteria for estimating pain severity, and for the first time, the basis of a system for routine pain assessment and management in rats subjected to abdominal surgery.