dihydromorphine and morphiceptin

The characteristics of opiate binding sites in the retina of the chick, rabbit and goldfish have been investigated. In the newly hatched chick retina, 131 fmol/mg of binding sites for [D-Ala2-D-Leu5]-[3H]enkephalin are present; competition studies with the delta selective peptide [D-Thr-Leu5]-enkephalin (DTLET) and the mu selective peptide morphiceptin show that all of the [D-Ala2-D-Leu5]-[3H]-enkephalin binding sites are of the delta subtype. Dihydro[3H]morphine binds poorly to the chick retina; 13.2 fmol/mg of this binding is displaceable by morphiceptin and corresponds to mu binding sites. Benzomorphan sites are defined as sites occupied by [3H]diprenorphine which is displaceable by low concentrations of ethylketocyclozacine but not by high concentrations of D-Ala2-D-Leu5-enkephalin and morphiceptin. At least 88 fmol/mg of benzomorphan sites are present in the chick retina. [3H]diprenorphine binding to the rabbit and fish retina was measured. The rabbit retina bound 60 fmol/mg, and the fish retina 42 fmol/mg of [3H]diprenorphine. These findings are discussed in the light of the studies on the localization and physiological effects of enkephalin in the retina.

Topics: Animals; Benzomorphans; Chickens; Dihydromorphine; Diprenorphine; Endorphins; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Goldfish; Oligopeptides; Rabbits; Receptors, Opioid; Retina; Species Specificity

Topics: Animals; Benzomorphans; Binding Sites; Brain; Cattle; Dihydromorphine; Endorphins; Etorphine; In Vitro Techniques; Morphinans; Rats; Receptors, Opioid; Retina; Tritium

The synthetic peptide NH2-Tyr-Pro-Phe-Pro-CONH2 (morphiceptin), which is the amide of a fragment of the milk protein beta-casein, has morphinelike activities and is highly specific for morphine (mu) receptors but not for enkephalin (delta) receptors. It is as active as morphine in the guinea pig ileum but much less active in the mouse and rat vas deferens. The discovery of this specific morphine receptor ligand substantiates the hypothesis of multiple opiate receptors. The ligand, which may be of physiological significance since a very similar, or identical, activity can be detected in enzymatic digests of beta-casein, may prove useful for further investigation of the functions of opiate receptor subtypes.

Topics: Animals; Binding, Competitive; Caseins; Dihydromorphine; Endorphins; Enkephalins; Guanosine Triphosphate; Guinea Pigs; Ileum; Male; Mice; Naloxone; Rats; Receptors, Opioid; Sodium; Vas Deferens