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KMID : 0811720010050000165
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Korean Journal of Physiology & Pharmacology
2001 Volume.5 No. 0 p.165 ~ p.0
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Peripherally Delivered Endomorphin 1 Attenuates Inflammatory Pain by Carrageenan
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Lee Seo-Eun
An Su-Kyung
Kim Jin-Hyuk
Shin Hong-Kee
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Abstract
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Endomorphins, recently found endogenous opioid peptides, have analgesic effect when delivered on the spinal cord. They act through μ-opioid receptors, and from the study with laboratory animals their potency for pain relief is similar to morphine. Some studies showed the possibilities of analgesic effect by peripherally delivered opioid peptides but it is still obscure. And it is not studied whether peripherally delivered endomorpohins induce analgesic effects or not. We tried to determine the analgesic effect of endomorphin 1 on inflammatory pain-like behaviors. Male Sprague-Dawley rats were injected into the right paw with carrageenan suspension and exposed to mechanical stimuli and heat stimuli before and after the injection. Up & down method for 50% withdrawal mecahnical threshold with von Frei hair and Hargreaves’ test with high intensity beam profection for heat sensitivity were used for pain measurement Endomorphin 1 was delivered into inflammatory area at the same time of carrageenan injection and after 6 hrs. Carrageenan injection decreased the withdrawal response thresholds to mechanical stimulus and latency to thermal stimulus clearly showing inflammatory hyperalgesia. Endomorphin-1 at high dose (20 μg), but not other lower doses, increased the pain threshold, both mechanical and thermal stimuli in the carrageenan injected animals significantly. From these results it could be concluded that endomorphin 1 weakly relieve inflammatory pain induced by carrageenan injected into paw. So peripheral μ-opioid receptors seem to contribute to opiate analgesia only in a small portion.
Source: Korean J Physiol Pharmacol.2001 Dec;5(Suppl II):S94
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