Evidence that beta-endorphin is an agonist at bovine pineal delta-opioid receptors.
Since beta-endorphin is the putative endogenous ligand for epsilon-opioid receptors, the previous demonstration of saturable, high affinity beta-endorphin binding sites on bovine pineal membranes suggests the possible presence of epsilon-opioid receptors. To determine the identity of pineal beta-endorphin binding sites, the inhibition of [125I]beta-endorphin binding by ligands with varying affinities for epsilon-, mu-, delta- or kappa-opioid receptors was investigated. A high positive correlation was observed between the Ki values for these drugs to inhibit [125I]beta-endorphin binding to pineal membranes and for these drugs to bind to delta-opioid receptors but not to mu-, kappa- or epsilon-opioid receptors, demonstrating that in the pineal beta-endorphin binds to delta-opioid receptors. Both NaCl and a GTP analogue were potent inhibitors of [125I]beta-endorphin binding, providing evidence that beta-endorphin is an agonist at pineal delta-opioid receptors. These results suggest that endogenous bovine beta-endorphin may modulate pineal function.
Aloyo
V J
VJ
Department of Pharmacology, Medical College of Pennsylvania, Philadelphia, USA.
Pazdalski
P S
PS
D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D010870:Pineal Gland / Q000378:metabolism*; D017465:Receptors, Opioid, delta / Q000819:agonists*; D001615:beta-Endorphin / Q000494:pharmacology*
D017465:Receptors, Opioid, delta; D006165:Guanylyl Imidodiphosphate; D009270:Naloxone; D009271:Naltrexone; D001615:beta-Endorphin; C055382:naltrindole