Effects of Repeated Administration of a κ-Opioid Agonist on Phorbol Ester Binding to Membrane-Bound Protein Kinase C in Rat Brain

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The dissociation constant (K_D) of [³H] phorbol 12, 13-dibutyrate (PDBu) binding to protein kinase C (PKC) in membranes of rat cortex and midbrain was significantly decreased with no change in the receptor density (B_max) following 7-d treatment with a κ-opioid agonist, U-50, 488 (20mg/kg/d, i.p.). Neither the B_max nor K_D values in pons/medulla were altered by repreated U-50, 488 treatment. These results suggest that repeated administration of a κ-opioid agonist increases the affinity for PDBu binding to the membrane-bound PKC in rat cortex and midbrain, but not in pons/medulla.