Effects of chronic administration of 7-benzylidene-7-dehydronaltrexone and naltriben on the antinociceptive actions of delta 1- and delta 2-opioid receptor agonists.
The effects of chronic administration of 7-benzylidene-7-dehydronaltrexone, a delta 1-opioid receptor antagonist and naltriben, a delta 2-opioid receptor antagonist, on the antinociceptive responses to [D-Pen2, D-Pen5] enkephalin and [D-Ala2, Glu4]deltorphin II, delta 1- and delta 2-opioid receptor agonists, respectively, were determined in the mouse. Female B6C3F1 mice were given 7-benzylidene-7-dehydronaltrexone (3 mg/kg/day), naltriben (1 mg/kg/day) or the vehicle by subcutaneously implanted Alzet osmotic minipumps for 7 days. Both [D-Pen2, D-Pen5]enkephalin and [D-Ala2, Glu4]deltorphin II administered intracerebroventricularly (i.c.v.) produced antinociceptive as measured by the tail-flick test with ED50 values of 6.76 and 6.68 micrograms/mouse, respectively. Chronic administration of 7-benzylidene-7-dehydronaltrexone lowered the ED50 of [D-Pen2, D-Pen5]enkephalin but not of [D-Ala2, Glu4]deltorphin II. Chronic administration of naltriben lowered the ED50 of [D-Ala2, Glu4]deltorphin II but had no effect on the ED50 of [D-Pen2, D-Pen5]enkephalin. The binding of [3H][D-Pen2, D-Pen5]enkephalin to whole brain membranes of chronic 7-benzylidene-7-dehydronaltrexone-treated mice did not differ from chronic vehicle-treated mice. On the other hand, chronic administration of naltriben resulted in slight but reproducible elevation in the Bmax value of [3H][D-Pen2, D-Pen5]enkephalin to bind to whole brain membranes in comparison to vehicle-injected controls. The results suggest that chronic treatment with delta 1- and delta 2-opioid receptor antagonist cause behavioral supersensitivity to their agonists, respectively, and provides further evidence for the existence of delta-opioid receptor subtypes.
Bhargava
H N
HN
Department of Pharmaceutics and Pharmacodynamics (M/C 865), University of Illinois at Chicago 60612, USA. drhnb@uic.edu
Zhao
G M
GM
House
R V
RV
Thomas
P T
PT
D000818:Animals; D001921:Brain / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004745:Enkephalins / Q000494:pharmacology; D005260:Female; D008566:Membranes / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009842:Oligopeptides / Q000378:metabolism* / Q000494:pharmacology; D010147:Pain Measurement / Q000187:drug effects*; D011957:Receptors, Opioid / Q000502:physiology; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors*
D004745:Enkephalins; D009292:Narcotic Antagonists; D009842:Oligopeptides; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; C068868:naltrindole benzofuran; C060209:deltorphin II, Ala(2)-; D009271:Naltrexone