European journal of pharmacology
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We assume that phenylephrine produces late pharmacological preconditioning through the opening of the mitochondrial KATP channels. To test this hypothesis, rat hearts were isolated and perfused with Krebs buffer solution by Langendorff method and subjected to 30 min regional ischemia followed by 60 min of reperfusion. In this study, phenylephrine as a selective alpha1-adrenoceptor agonist and 5HD (5-hydroxydecanoate) as a putatively specific blocker of the mitochondrial KATP channels were used. ⋯ Compared to ischemia/reperfusion group, phenylephrine in early and late phases decreased myocardial infarct size (% of ischemia zone), reduced CK-MB (Creatine Kinase-MB) release in the coronary effluent and improved cardiac function. Pretreatment with 5HD abolished phenylephrine-induced cardioprotection in early and late phases. It is concluded that phenylephrine-induced late cardioprotection was abolished by administration of 5HD in the isolated rat hearts.
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Itching is known as a commonly side effect of opioid administration. However, the relationship of opioid receptors to itching is unclear. In this study, we examined the effect of intradermal injection of morphine and fentanyl on the itching sensation. ⋯ Additionally, scratching behavior induced by morphine and fentanyl were not suppressed by glucocorticoids (predonisolone and dexamethasone). In conclusion, opioid-induced itching may involve in peripheral opioid receptors. Moreover, histamine and arachidonic acid metabolites played no main role in opioid-induced scratching behavior.
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Brain neuronal histamine, through its receptors, is involved in central pain perception. In the present study, the effect of microinjection of histamine, mepyramine (a histamine H(1) receptor antagonist) and ranitidine (a histamine H(2) receptor antagonist) into the dorsal hippocampus was investigated on a model of orofacial pain in rats. Orofacial pain was induced by subcutaneous injection of formalin (1%, 50 microl) in the upper lip in rats, and the time spent of face rubbing was measured in 3-min blocks for 45 min. ⋯ Pretreatments with mepyramine and ranitidine at a same dose of 4 microg prevented histamine (1 microg)-induced antinociception. These results indicate that the activation of brain neuronal histamine at the levels of the hippocampus may produce antinociception. Hippocampal histamine-induced antinociception may be mediated thorough its H(1) and H(2) receptors.