dynorphins and normorphine

In the mouse isolated vas deferens the amplitude of excitatory junction potentials (e.j.p.s) recorded intracellularly from smooth muscle cells varied with the strength of stimulation. Receptor type selective opioids were tested in this preparation. The mu-agonist normorphine (2,000 nmol/l) reduced the amplitude of e.j.p.s and shifted the stimulus-response curve in a parallel way to the right. By contrast, the kappa-agonist U-50488 (1,000 nmol/l) and the delta-agonist [D-Ala2,D-Leu5]-enkephalin (2 nmol/l) caused a non-parallel shift of the curve. In addition, opioids having a lower selectivity for one type of receptor were also used. The preferential kappa-agonists ethylketocyclazocine (40 nmol/l) and dynorphin A1-13 (100 nmol/l) produced parallel and non-parallel shifts, respectively. Thus, normorphine and ethylketocyclazocine were more effective in depressing e.j.p.s evoked by low intensities of stimulation than those evoked by high intensities of stimulation. U-50488, dynorphin A1-13 and [D-Ala2,D-Leu5]-enkephalin caused an equal depression of e.j.p.s evoked by either intensity of stimulation. The preferential mu- and delta-antagonists naloxone (1,000 nmol/l) and ICI 154129 (10,000 nmol/l), reversed the action of the respective agonists normorphine and [D-Ala2, D-Leu5]-enkephalin. In addition, ICI 154129 (10,000 nmol/l) reversed the action of dynorphin A1-13, as well. The preferential kappa-antagonist MR-2266 (1,000 nmol/l) prevented the effect of both ethylketocyclazocine and U-50488. It is concluded that under the conditions of these experiments normorphine and ethylketocyclazocine acted at mu-, U-50488 at kappa-, and dynorphin A1-13 and [D-Ala2,D-Leu5]-enkephalin at delta-receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Cyclazocine; Dynorphins; Electric Stimulation; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Ethylketocyclazocine; In Vitro Techniques; Male; Mice; Morphine Derivatives; Muscle, Smooth; Neuromuscular Junction; Pyrrolidines; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Synaptic Transmission

The electrophysiological actions of normorphine and dynorphin-A were compared in the dentate gyrus and CA1 regions of the rat hippocampus. In both regions, these opioids increased cell excitability and induced afterpotentials following electrical stimulation of synaptic afferents. Based upon apparent naloxone dissociation constants, we conclude that normorphine activated mu receptors in both regions. However, dynorphin-A appears to act via mu receptors in CA1, but kappa receptors in the dentate gyrus.

Topics: Animals; Dynorphins; Hippocampus; In Vitro Techniques; Membrane Potentials; Morphine Derivatives; Naloxone; Pyramidal Tracts; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, kappa; Receptors, Opioid, mu

Extraluminal strain gage transducers were sutured along the transverse axis of the duodenum in order to monitor circular muscle contractile activity in the pentobarbital anesthetized dog. Administration by intravenous bolus of a variety of mu- and delta-directed opioid ligands resulted in a dose-dependent increase in duodenal contractile activity. In contrast, all kappa-directed ligands were devoid of stimulatory activity. Naloxone reversed the effects of normorphine and [Met5]enkephalin but was 20 times more effective against normorphine than [Met5]enkephalin. Based on the inactivity of all kappa ligands examined and the differential potency of naloxone against [Met5]enkephalin and normorphine, we suggest that this model may be useful in the classification of opioid ligands as to their receptor selectivity in vivo. Further, these data indicate that the stimulation of duodenal contractile activity is not mediated by enteric kappa receptors.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Dogs; Duodenum; Dynorphins; Electric Stimulation; Enkephalin, Methionine; Female; Gastrointestinal Motility; Male; Morphine; Morphine Derivatives; Naloxone; Peptide Fragments; Phenazocine; Pyrrolidines; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu

In the guinea pig ileum myenteric plexus--longitudinal muscle preparation, dynorphin-(1--13) and the prototypical kappa agonist ethylketocyclazocine had equally poor sensitivity to naloxone antagonism and showed selective cross protection in receptor inactivation experiments with the alkylating antagonist beta-chlornaltrexamine. In binding assays with membranes from guinea pig brain, ethylketocyclazocine and dynorphin-(1--13) amide were more potent in displacing tritium-labeled ethylketocyclazocine than in displacing typical mu and delta opioid receptor ligands. In the two preparations studied, the dynorphin receptor appears to be the same as the kappa opioid receptor.

Topics: Analgesics, Opioid; Animals; Binding, Competitive; Brain; Cyclazocine; Dynorphins; Endorphins; Enkephalin, Leucine; Enkephalins; Ethylketocyclazocine; Guinea Pigs; In Vitro Techniques; Ligands; Morphine Derivatives; Myenteric Plexus; Naloxone; Peptide Fragments; Receptors, Opioid

To test the hypothesis that dynorphin is a K-opiate agonist acting on the myenteric plexus, the potency of two benzomorphan antagonists (Win 44, 441 and Mr 2266) to block the inhibitory action of dynorphin, enkephalins and opioid alkaloids was determined on the longitudinal muscle preparation of the guinea pig ileum. The effectiveness of these antagonists was compared to that of naloxone. Antagonistic potency was established by calculating the apparent antagonist dissociation constant, Ke, as derived from Schild plots. Win 44, 441 and Mr 2266 were about 7-8 times more potent than naloxone against dynorphin, dynorphin-(1-13) or ethylketocyclazocine. Although the Ke obtained with Win 44, 441 or Mr 2266 against dynorphin or ethylketocyclazocine were significantly lower than those of naloxone, the values obtained for these antagonists did not differ significantly in the case of each of these agonists. With respect to the antagonism of the enkephalins or normorphine, Win 44, 441 was the most potent antagonist. Its Ke value for the enkephalins was 2.5-3 times lower than those for dynorphin or ethylketocyclazocine and in comparison to naloxone, Win 44, 441 was about 5 times more potent. Although Mr 2266 was a potent antagonist of dynorphin, ethylketocyclazocine, the enkephalins or normorphine, it showed no selectivity of action. The fact that the 3 opiate antagonists evidenced similar Ke values for dynorphin and ethylketocyclazocine, but different ones for the enkephalins or normorphine supports the conclusion that dynorphin activates preferentially K- but not mu-opiate receptors in the myenteric plexus.

Topics: Animals; Azocines; Benzomorphans; Cyclazocine; Dynorphins; Endorphins; Enkephalins; Ethylketocyclazocine; Guinea Pigs; Ileum; In Vitro Techniques; Male; Morphine Derivatives; Muscle, Smooth; Naloxone; Narcotic Antagonists

Application of 100 nM beta-FNA for 60 minutes to isolated longitudinal muscles-myenteric plexus preparations from the guinea pig ileum caused a marked antagonism of the inhibitory action of normorphine and leucine enkephalin without greatly affecting the inhibitory potency of dynorphin or ethylketocyclazocine. The interaction of beta-FNA with the normorphine (mu-opiate receptors) appears to be non-equilibrium. Pretreatment with beta-FNA caused a significant increase in the apparent naloxone dissociation constant for normorphine and leucine enkephalin but not for dynorphin or ethylketocyclazocine. The results lend further support to the hypothesis that normorphine and the enkephalins activate preferentially mu-opiate receptors on the ileum, whereas dynorphin interacts predominantly at k-opiate sites.

Topics: Animals; Binding, Competitive; Dose-Response Relationship, Drug; Dynorphins; Electric Stimulation; Endorphins; Guinea Pigs; Morphine Derivatives; Muscle, Smooth; Naloxone; Naltrexone; Receptors, Opioid; Time Factors