Effect of dexmedetomidine on visceral pain in rats: the role of α2 adrenergic receptors in locus coeruleus

Objective To evaluate the effect of dexmedetomidine on visceral pain in rats and the role of α2 adrenergic receptors in locus coeruleus (LC). Methods Thirty-two healthy adult male Sprague-Dawley rats, weighing 250-300 g, were divided into 4 groups (n=8 each) using a random number table method: control group (group C), visceral pain group (group VP), dexmedetomidine group (group DEX) and α2-adrenergic receptor antagonist atipamezole group (group AP). α2-adrenergic receptor antagonist atipamezole 522 μg/kg was intramuscularly injected in group AP, and the equal volume of normal saline was given instead in C, VP and DEX groups.At 10 min after intramuscular injection, dexmedetomidine 10 μg/kg was injected via the tail vein in DEX and AP groups, and the equal volume of normal saline was given instead in C and VP groups.VP, DEX and AP groups received intraperitoneal injection of 0.9% acetic acid 10 ml/kg to make the visceral pain model at 15 min after injection via the tail vein.The cumulative visceral pain score was recorded within 60 min after acetic acid injection.The number of c-fos positive cells in LC was detected by immunohistochemistry, and the content of norepinephrine (NA) in the spinal cord were detected by enzyme-linked immunosorbent assay at 2 h after acetic acid injection. Results Compared with group C, the cumulative visceral pain scores, the number of c-fos positive cells in LC and content of NA in the spinal cord were significantly increased in VP, DEX and AP groups (P<0.05). Compared with group VP, the cumulative visceral pain scores, the number of c-fos positive cells in LC and content of NA in the spinal cord were significantly decreased in DEX and AP groups (P<0.05). Compared with group DEX, the cumulative visceral pain scores, the number of c-fos positive cells in LC and content of NA in the spinal cord were significantly increased in group AP (P<0.05). Conclusion Dexmedetomidine can alleviate visceral pain in rats, and the mechanism is partially related to activating α2 adrenergic receptors in LC. Key words: Dexmedetomidine; Visceral; Pain; Locus coeruleus; Receptors, adrenergic alpha-2