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KMID : 0848120120370010001
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International Journal of Oral Biology
2012 Volume.37 No. 1 p.1 ~ p.7
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Effects of Whole Body Irradiation on Morphine, DAMGO, DPDPE, U50,488H and β-endorphin-Induced Antinociception
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Chung Ki-Myung
Park Tae-Won
Kim Jin-Kyu
Jeong Jae-Soo
Kim Tae-Wan
Cho Young-Kyung
Kim Kyung-Nyun
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Abstract
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Opioid receptors have been pharmacologically classified as μ, δ, κ and ε. We have recently reported that the antinociceptive effect of morphine (a μ-opioid receptor agonist), but not that of β-endorphin (a novel μ/ε-opioid receptor agonist), is attenuated by whole body irradiation (WBI). It is unclear at present whether WBI has differential effects on the antinociceptive effects of μ-, δ-, κ- and ε-opioid receptor agonists. In our current experiments, male ICR mice were exposed to WBI (5Gy) from a 60 Co gamma-source and the antinociceptive effects of opioid receptor agonists were assessed two hours later using the hot water (52 o C) tail-immersion test. Morphine and D-Ala 2 ,N-Me-Phe 4 ,Gly-ol-enkephalin (DAMGO), [D-Pen 2 -D-Pen 5 ]enkephalin (DPDPE), trans-3,4-Dichloro-N-methyl-N-[2-(1-pyrrolidinyl)- cyclohexyl]￢benzeneacetamide (U50,488H), and β-endorphin were tested as agonists for μ, δ, κ, and ε-opioid receptors, respectively. WBI significantly attenuated the antinociceptive effects of morphine and DAMGO, but increased those of β-endorphin. The antinociceptive effects of DPDPE and U50,488H were not affected by WBI. In addition, to more preciously understand the differential effects of WBI on μ- and ε￢opioid receptor agonists, we assessed pretreatment effects of β-funaltrexamine (β-FNA, a μ-opioid receptor antagonist) or β-endorphin 1-27 (β-EP 1-27 , an ε-opioid receptor antagonist), and found that pretreatment with β-FNA significantly attenuated the antinociceptive effects of morphine and β endorphin by WBI. significantly reversed the β-EP 1-27 attenuation of morphine by WBI and significantly attenuated the increased effects of β-endorphin by WBI. The results demonstrate differential sensitivities of opioid receptors to WBI, especially for μ- and ε-opioid receptors.
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KEYWORD
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Opioid, Antinociception, Whole-body irradiation, β-funaltrexamine, β-endorphin1-27
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