• Y Harada, K Nishioka, L M Kitahata, K Kishikawa, and J G Collins.
• Department of Anesthesiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
• Anesthesiology. 1995 Aug 1; 83 (2): 344-52.

BackgroundVisceral pain is an important component of many clinical pain states. The perispinal administration of drug combinations rather than a single agent may reduce side effects while maximizing analgesic effectiveness. The purpose of this study was to examine the nature of interactions between an alpha 2-adrenergic agonist (clonidine) and a mu-opioid agonist (morphine), a delta-opioid agonist ([D-Pen2, D-Pen5] enkephalin [DPDPE]), or a kappa-opioid agonist (U50,488H).MethodsColorectal distension was used to elicit a nociceptive visceromotor response (contraction of abdominal musculature) in rats. The ability of intrathecally administered clonidine alone or in combination with morphine, DPDPE, or U50,488H to alter thresholds for the production of the visceromotor response was examined.ResultsClonidine produced dose-dependent reduction in threshold. U50,488H, at the doses tested, showed no synergistic interaction with clonidine.ConclusionsSpinal combinations of alpha 2-adrenergic and mu- or delta- but not kappa-opioid agonists may be beneficial in the control of visceral pain.

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