[Effects of ketamine on behavioral responses to somatic and visceral stimuli in rats]

The responses to colorectal distension as a visceral stimulus were observed and tail-flick test was performed in rats, after intraperitoneal administration of ketamine 30 mg.kg-1 (n = 6) or 100 mg.kg-1 (n = 5). After determining control colorectal distension and tail-flick values, both procedures were repeated every 10 minutes for one hour in both groups. The control thresholds for colorectal distension and tail-flick latencies were 20.8 +/- 1.0 mmHg and 4.5 +/- 0.3 sec (mean +/- SD), respectively in ketamine 30 mg.kg-1 group. They were 21.2 +/- 1.1 mmHg and 4.7 +/- 0.4 sec in ketamine 100 mg.kg-1 group. These baseline threshold and latency values in the two groups were not significantly different. Ten minutes after ketamine administration, the colorectal distension thresholds and tail-flick latencies were 43.7 +/- 7.2 mmHg and 6.4 +/- 0.9 sec, respectively in ketamine 30 mg.kg-1 group. They were 53.3 +/- 14.8 mmHg and 7.2 +/- 0.8 sec, respectively in ketamine 100 mg.kg-1 group. These values were significantly greater than the preketamine control values in both groups. The present study demonstrates that ketamine exerts apparent analgesic effects against both visceral and somatic stimuli. These results led us to consider that ketamine may be clinically useful to control visceral pain.