title: Decrease in delta-opioid receptor density in rat brain after chronic [D-Ala2,D-Leu5]enkephalin treatment.
abstract: Chronic treatment of Sprague-Dawley rats with [D-Ala2,D-Leu5]enkephalin (DADLE) resulted in the development of tolerance to the antinociceptive effect of this opioid peptide. When opioid receptor binding was measured, time-dependent decreases in [3H]diprenorphine binding to the P2 membranes prepared from the cortex, midbrain and striatum were observed. Scatchard analysis of the saturation binding data revealed a decrease in Bmax values and no change in the Kd values of [3H]diprenorphine binding to these brain regions, indicative of down-regulation of the receptor. This reduction in the opioid receptor binding activities could be demonstrated to be due to the DADLE effect on the delta-opioid receptors in these brain regions. When [3H]DADLE binding was carried out in the presence of morphiceptin, a significant reduction in the delta-opioid receptor binding was observed in all brain areas tested. mu-Opioid receptor binding decrease was observed only in the striatum after 5 days of DADLE treatment. Additionally, the onset of delta-opioid receptor decrease in the midbrain area was rapid, within 6 h of the initiation of the chronic DADLE treatment. Thus, analogous to previous observations in which chronic etorphine treatment preferentially reduced mu-opioid receptor binding, chronic DADLE treatment preferentially reduced delta-opioid receptor binding activity.
authors.affiliation: Department of Pharmacology, National Defense Medical Center, Taipei, Taiwan.
authors.forename: P L
authors.initials: PL
authors.lastname: Tao
authors.forename: L R
authors.initials: LR
authors.lastname: Chang
authors.forename: P Y
authors.initials: PY
authors.lastname: Law
authors.forename: H H
authors.initials: HH
authors.lastname: Loh
mesh_terms: D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D004174:Diprenorphine / Q000378:metabolism*; D004361:Drug Tolerance; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives* / Q000494:pharmacology; D016308:Enkephalin, Leucine-2-Alanine; D007700:Kinetics; D008297:Male; D009019:Morphinans / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000378:metabolism*; D017465:Receptors, Opioid, delta; D013997:Time Factors
chemical_list: D009019:Morphinans; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D004174:Diprenorphine; D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine