Prolonged in vivo antagonism of central mu- and delta-opioid receptor activity by beta-funal trexamine |
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Authors: | A Dray L Nunan W Wire |
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Institution: | Department of Pharmacology University of Arizona Health Sciences Center College of Medicine Tucson, Arizona, 85724, U.S.A. |
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Abstract: | beta-Funaltrexamine (beta-FNA) was tested in the spinal cord and supraspinally against inhibition of reflex bladder contractions produced in the anesthetized rat by the opioid-receptor selective agonists D-Ala2, MePhe4, Gly (ol)5]enkephalin (DAGO, mu-agonist) and D-Pen2, D-Pen5] enkephalin (DPDPE, delta-agonist). All agents were microinjected either intracerebroventricularly (i.c.v.) or intrathecally (i.t.). beta-FNA (1-8 micrograms) produced long-lasting antagonism of both DAGO and DPDPE. Complete recovery from its effects was only observed some 24-32 h later. Higher doses of beta-FNA (4 and 8 micrograms i.t.) produced short-lived agonistic activity though the selectivity of this was not determined. It was concluded that beta-FNA was a potent, long-lasting antagonist at central opioid receptors in vivo but was unselective for the mu and delta opioid receptor. |
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