Effect of detomidine on visceral and somatic nociception and duodenal motility in conscious adult horses

Objective To evaluate the effects of detomidine on visceral and somatic nociception, heart and respiratory rates, sedation, and duodenal motility and to correlate these effects with serum detomidine concentrations. Study design Nonrandomized, experimental trial. Animals Five adult horses, each with a permanent gastric cannula weighing 534 ± 46 kg. Methods Visceral nociception was evaluated by colorectal (CRD) and duodenal distension (DD). The duodenal balloon was used to assess motility. Somatic nociception was assessed via thermal threshold (TT). Nose–to–ground (NTG) height was used as a measure of sedation. Serum was collected for pharmacokinetic analysis. Detomidine (10 or 20 μg kg −1 ) was administered intravenously. Data were analyzed by means of a three–factor anova with fixed factors of treatment and time and random factor of horse. When a significant time × treatment interaction was detected, differences were compared with a simple t –test or Bonferroni t –test. Significance was set at p Results Detomidine produced a significant, dose–dependent decrease in NTG height, heart rate, and skin temperature and a significant, nondose–dependent decrease in respiratory rate. Colorectal distension threshold was significantly increased with 10 μg kg −1 for 15 minutes and for at least 165 minutes with 20 μg kg −1 . Duodenal distension threshold was significantly increased at 15 minutes for the 20 μg kg −1 dose. A significant change in TT was not observed at either dose. A marked, immediate decrease in amplitude of duodenal contractions followed detomidine administration at both doses for 50 minutes. Conclusions and clinical relevance Detomidine caused a longer period of visceral anti–nociception as determined by CRD but a shorter period of anti–nociception as determined by DD than has been previously reported. The lack of somatic anti–nociception as determined by TT testing may be related to the marked decrease in skin temperature, likely caused by peripheral vasoconstriction and the low temperature cut–off of the testing device.