dynorphins and chlornaltrexamine

beta-Chlornaltrexamine (beta-CNA) is a non-equilibrium opioid receptor antagonist which alkylates and inactivates opioid receptors. Because opioid peptides are thought to contribute to the regulation of food intake, we examined the effects of intracerebroventricular (icv) injections of beta-CNA on the food intake and body weight of male rats. We also tested the ability of beta-CNA to block food intake stimulated by selective agonists of kappa, mu and delta opioid receptors: dynorphin A2 (DYN), Tyr-D-Ala-Gly-(Me)Phe-Gly-ol (DAGO), and [(D-Ser2,Leu5]-enkephalin-Thr6 (DSLET). Treatment with beta-CNA caused a long-term (2-4 days) reduction in daily food intake and a concomitant reduction in body weight. An additional experiment indicated that the weight loss after beta-CNA treatment could be completely accounted for by the reduction in intake. beta-CNA treatment also abolished or greatly attenuated the feeding effects of DAGO, DSLET and DYN, even when these peptides were tested 26 hours after beta-CNA administration. The long duration of the effects of beta-CNA suggests that this compound will be a useful pharmacological tool in further study of the opioid feeding system.

Topics: Animals; Body Weight; Dynorphins; Eating; Endorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalins; Male; Naltrexone; Oligopeptides; Rats; Rats, Inbred Strains; Receptors, Opioid

The opioid receptor antagonists, naloxone and beta-chlornaltrexamine, were used to determine whether activation of endogenous opioid peptide containing pathways produced pharmacologically reversible opioid actions. Extracellularly recorded responses of the hippocampal CA3 pyramidal cells were evoked by stimulation of the dynorphin-containing mossy fiber pathway. Neither naloxone nor beta-chlornaltrexamine pretreatment significantly changed the evoked response. However, both antagonists blocked the effect of applied dynorphin-A(1-17) on CA1 pyramidal cell evoked responses. Thus, our data demonstrate that if endogenous opioids are released from this pathway, the peptides cannot be responsible for the evoked response measured in hippocampal CA3 cellular field. With no direct evidence for endogenous opioid peptides acting through opioid receptors, the neurotransmitter role of dynorphins in rat hippocampus remains obscure.

Topics: Animals; Dynorphins; Endorphins; Evoked Potentials; Hippocampus; In Vitro Techniques; Naloxone; Naltrexone; Peptide Fragments; Rats; Synaptic Transmission

We have previously demonstrated that [3H]dynorphin A selectively labels kappa opioid receptors in guinea-pig whole brain. In these current studies, using protection from inactivation by beta-chloronaltrexamine (beta-CNA), we are able to demonstrate that although dynorphin A prefers kappa receptors, it will label mu receptors when kappa receptors are not available, or present in only a small number. Thus, differences in numbers of mu and kappa receptors present in brain preparations are critical in determining the receptor binding profile of [3H]dynorphin A across species. Additionally, although all the prodynorphin derived peptides show kappa preference, the ability of the other prodynorphin derived peptides to compete with [3H]dynorphin A for its receptor varies across species. Consequently, in a highly enriched kappa preparation such as monkey cerebral cortex, [3H]dynorphin A appears to label kappa receptors with substantial selectivity, and the other prodynorphin-derived peptides show less ability to compete with dynorphin A for its receptor. In contrast, in a kappa-poor tissue such as rat brain, all of the prodynorphin-derived peptides, including dynorphin A-(1-8), show very similar potency. Thus, differences in mu and kappa receptor numbers across brain regions and species lead to differences in the receptor binding profile of dynorphin A.

Topics: Alkylating Agents; Animals; Benzomorphans; Brain Chemistry; Dynorphins; Guinea Pigs; In Vitro Techniques; Macaca mulatta; Morphine; Naltrexone; Peptides; Rats; Receptors, Opioid; Receptors, Opioid, kappa; Receptors, Opioid, mu; Stereoisomerism

In the guinea-pig ileum myenteric plexus-longitudinal muscle preparation, products from the dynorphin gene fell into three groups according to their potency. Dynorphin A was the most potent; dynorphin-32, dynorphin B, dynorphin B-29 and alpha-neo-endorphin were about equipotent and 10 to 20 times less potent than dynorphin A; dynorphin A-(1-8) and beta-neo-endorphin were about 200 times less potent than dynorphin A. Dynorphin A (a kappa agonist) was about 10 times less sensitive to antagonism by naloxone (as measured by naloxone Ke) than was normorphine (a mu agonist). Ke values for dynorphin-32, dynorphin B and alpha-neo-endorphin were the same as for dynorphin A, indicating that these peptides are also highly selective kappa agonists. Dynorphin A-(1-8), dynorphin B-29 and beta-neo-endorphin had Ke values intermediate between dynorphin A and normorphine, suggesting that they interact at both kappa and mu receptors. Addition of peptidase inhibitors to the bathing medium increased the potencies of dynorphin B, dynorphin B-29, alpha-neo-endorphin, dynorphin A-(1-8) and beta-neo-endorphin, but not of dynorphin A, dynorphin-32 or normorphine. The inhibitors did not change the naloxone Ke for dynorphin A or normorphine, or for dynorphin B-29, dynorphin A-(1-8) and beta-neo-endorphin, suggesting that the intermediate values were not caused by degradation to products with different receptor selectivities from the parent compounds. Ke for dynorphin-32, dynorphin B and alpha-neo-endorphin changed from being the same as dynorphin A in the absence of inhibitors to intermediate between dynorphin A and normorphine in the presence of inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Dynorphins; Endorphins; Enkephalin, Leucine; Guinea Pigs; Ileum; In Vitro Techniques; Male; Muscle Contraction; Muscle, Smooth; Myenteric Plexus; Naloxone; Naltrexone; Peptide Fragments; Protein Precursors; Receptors, Opioid

Topics: Animals; Dose-Response Relationship, Drug; Dynorphins; Endorphins; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Guinea Pigs; Ileum; Male; Mice; Muscle Contraction; Muscle, Smooth; Naloxone; Naltrexone; Receptors, Opioid; Receptors, Opioid, kappa; Structure-Activity Relationship; Vas Deferens

Opioid receptors on guinea pig brain membranes were alkylated by the naltrexone analogue beta-chlornaltrexamine. Binding of the prototypical mu and kappa ligands, [3H]dihydromorphine and [3H]ethylketocyclazocine, was more readily affected by the reagent than was binding of the delta ligand, 3H-labeled [D-Ala2, D-Leu5]enkephalin. Treatment of membranes with beta-chlornaltrexamine in the presence of dynorphin resulted in significant protection of [3H]ethylketocyclazocine binding sites, without protection of [3H]dihydromorphine or 3H-labeled [D-Ala2, D-Leu5]enkephalin sites. Similarly, [D-Ala2, D-Leu5]enkephalin and sufentanil selectively protected binding sites for 3H-labeled [D-Ala2, D-Leu5]enkephalin and [3H]dihydromorphine, respectively. Scatchard analysis of [3H]ethylketocyclazocine binding to untreated membranes suggested two types of binding site with 40-fold difference in affinities. Membranes treated with beta-chlornaltrexamine in the presence of dynorphin retained about 40% of the high-affinity sites and lost the low-affinity sites. Selective protection of sites with high affinity for dynorphin and ethylketocyclazocine was confirmed in competition binding assays. These results strongly suggest that the three types of opioid receptor are not interconvertible and provide further evidence that the endogenous peptide dynorphin is a highly selective ligand of the kappa opioid receptor.

Topics: Animals; Brain Chemistry; Cell Membrane; Dynorphins; Endorphins; Guinea Pigs; Ligands; Naloxone; Naltrexone; Receptors, Opioid

Topics: Animals; Binding, Competitive; Dynorphins; Endorphins; Enkephalin, Leucine; Enkephalins; Guinea Pigs; Ileum; Kinetics; Muscle Contraction; Myenteric Plexus; Naltrexone; Narcotic Antagonists; Narcotics; Nitrogen Mustard Compounds; Peptide Fragments; Receptors, Opioid