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Chronic morphine upregulates a mu-opiate binding site labeled by [3H]cycloFOXY: a novel opiate antagonist suitable
R B Rothman1, S McLean, V Bykov
1Laboratory of Preclinical Pharmacology, St. Elizabeths Hospital, NIMH, Washington, DC 20032.
Abstract:
CycloFOXY (17-cyclopropylmethyl-3,14-dihydroxy-4,5-alpha-epoxy-6-beta- fluoromorphinan) is a novel opiate antagonist synthesized as a ligand suitable for in vivo visualization of opiate receptors using positron emission transaxial tomography. In this paper we report that [3H]cycloFOXY labels two distinct opiate binding sites in rat brain membranes, tentatively identified as mu and kappa. Furthermore, chronic administration of morphine results in a selective up-regulation of the mu binding site. The implications of this finding for models of the opioid receptors and the mechanism of the sodium effect are discussed.