Anger regulation style, postoperative pain, and relationship to the A118G mu opioid receptor gene polymorphism: a preliminary study.

Greater trait anger-out is associated with elevated pain responsiveness. Previous work suggests this effect may be mediated by deficient endogenous opioid analgesia, possibly reflecting diminished opioid receptor sensitivity. The A118G single nucleotide polymorphism (SNP) of the mu opioid receptor gene influences both opioid receptor sensitivity and clinical responsiveness to opioid analgesics. Therefore, this study tested whether this SNP either mediated or moderated the effects of anger-out on postsurgical pain outcomes. Forty-eight patients undergoing coronary artery bypass graft surgery provided genetic samples, and completed measures of anger-out and postsurgical pain. Postsurgical opioid analgesic use was also recorded. Anger-out was positively associated with postsurgical pain ratings (p < 0.05). Anger-out was not associated with A118G SNP status (p > 0.10), suggesting the latter is unlikely to mediate anger-out's pain-related effects. A significant anger-out x A118G interaction was observed on analgesic use (p < 0.05), due to a much stronger positive relationship between anger-out and analgesic demands in patient with the A118G SNP (b = 0.53) than those with the wild-type receptor (b = 0.07). These results suggest that the A118G SNP may moderate but not mediate the effects of anger-out on postoperative pain responses.