[Differential effects of morphine and non-steroidal anti-inflammatory drugs on somatic and visceral pain in rats].

We studied the differential effects of morphine and non-steroidal anti-inflammatory drug (NSAIDs) on behavioral responses to tail-flick (TF) and colorectal distension (CD) in rats. Animals were randomly divided into three groups; morphine groups (4 mg.kg-1), flurbiprofen axetil groups (30 mg.kg-1) and aspirin DL-lysin groups (100 mg.kg-1). After determining control TF and CD values, animals received each analgesic intraperitoneally, and each procedure was repeated every 10 minutes for 30 or 40 minutes. NSAIDs produced a statistically significant increase in pain threshold for CD, but not for TF. In contrast, almost similar patterns of increase in pain thresholds for CD and TF were observed in morphine groups. The present study demonstrates that NSAIDs have a powerful antinociceptive effect on visceral pain evoked by CD.