Analysis of the effect of neuropeptides and cannabinoids in gastric mucosal defense initiated centrally in the rat.

Increasing number of evidence suggest that gastric mucosal protection can be induced also centrally. Several neuropeptides, such as TRH, amylin, adrenomedullin, enkephalin, beta-endorphin, nociceptin, nocistatin, ghrelin or orexin given centrally induce gastroprotection and the dorsal vagal complex and vagal nerve may play prominent role in this centrally initiated effect. Since also cannabinoid receptors are present in the dorsal vagal complex, we aimed to study whether activation of central cannabinoid receptors result in gastric mucosal defense and whether there is an interaction between cannabinoids and endogenous opioids. Gastric mucosal damage was induced by 100% ethanol in rats. The cannabinoids were given intravenously (i.v.) or intracerebroventricularly (i.c.v.), while the antagonists were given i.c.v or intracisternally (i.c.). Gastric lesions were evaluated macroscopically 60 min later. Anandamide, methanandamide and WIN55,212-2 reduced ethanol-induced mucosal lesions after both peripheral (0.28-5.6 micromol/kg, 0.7-5.6 micromol/kg and 0.05-0.2 mumol/kg i.v., respectively) and central (2.9-115 nmol/rat, 0.27-70 nmol/rat and 1.9-38 nmol/rat i.c.v., respectively) administration. The gastroprotective effect of anandamide and methanandamide given i.c.v. or i.v.was reversed by the CB(1) receptor antagonist SR141716A (2.16 nmol i.c.v.). Naloxone (27.5 nmol i.c.v.) also antagonized the effect of i.c.v. or i.v. injected anandamide and WIN55,212-2, but less affected that of methanandamide. The gastroprotective effect of anandamide was diminished also by endomorphin-2 antiserum. In conclusion it was first demonstrated that activation of central CB(1) receptors results in gastroprotective effect. The effect is mediated at least partly by endogenous opioids.

Side chain modifications change the binding and agonist properties of endomorphin 2.

Side chain modifications were introduced to endomorphin 2 (E2) to improve its binding properties and biological activity. A number of C-terminal modifications decreased the binding affinity to the mu-opioid receptor and the intrinsic activity in rat brain membranes. The exception was E2-ol, which showed increased binding affinity to MOR and higher potency in stimulating [(35)S]GTPgammaS binding. N-methylation of Phe(3) (MePhe(3)) attenuated the binding affinity and produced a rightward shift of [(35)S]GTPgammaS binding curves. All derivatives had lower intrinsic activity than E2. Some of the modified peptides partially inhibited, while YPF-benzyl-allyl-amide fully inhibited, the E2 or [d-Ala(2),MePhe(4),Gly(5)ol]enkephalin stimulated [(35)S]GTPgammaS binding. Marked differences were found between the results obtained using tritiated E2, tritiated naloxone, and [(35)S]GTPgammaS binding, indicating the possible involvement of multiple binding sites. The data presented demonstrate that the C-terminal amide group has an essential role in the regulation of the binding and the agonist/antagonist properties of E2.

Activation of central opioid receptors may induce gastric mucosal defence in the rat.

The effect of different opioid peptides on acidified ethanol- and indomethacin-induced gastric mucosal lesions was studied following intracerebroventricular (i.c.v.) administration. It was found that both the selective delta opioid receptor agonists--deltorphin II, [D-Ala(2), D-Leu(5)]-enkephalin (DADLE), [D-Pen(2), D-Pen(5)]-enkephalin (DPDPE)-, mu-opioid receptor agonist--[D-Ala(2), Phe(4), GlyT-ol]-enkephalin (DAGO)--as well as beta-endorphin inhibited the mucosal damage induced by both ethanol and indomethacin in pmolar dose range. In contrast, the gastric acid secretion was not influenced by DADLE in the dose of 16 nmol/rat and only a slight reduction (40%) was induced by DAGO in the dose of 1.9 nmol/rat. The protective effect was abolished in both ulcer models by bilateral cervical vagotomy. N(G)-nitro-L-arginine, an inhibitor of NO synthase, reduced the protective action in ethanol-induced, but not in indomethacin-induced gastric damage. The results suggest that activation of supraspinal delta and mu-opioid receptors resulted in inhibition of gastric mucosal lesions elicited by ethanol or indomethacin. The gastroprotective action is independent from the effect of opioids on acid secretion. Vagal nerve is involved in conveying the central action to the periphery. The mechanism of the gastroprotective effect of opioids is different in ethanol- and indomethacin-ulcer models: prostaglandins and nitric oxide are likely to be involved in the protective action of opioid peptides in ethanol-, but not in the indomethacin-ulcer model.

Neonatal monosodium glutamate treatment abolishes both delta opioid receptor-induced and alpha-2 adrenoceptor-mediated gastroprotection in the lower brainstem in rats.

Neonatal monosodium glutamate treatment reduced immunoreactive beta-endorphin content in the mediobasal hypothalamus by 50% in adult, male Wistar rats as compared to hypertonic saline-treated littermates; there was also a moderate (approx. 25%) reduction in the rostral part of the nucleus of the solitary tract. In sham-treated adults the intracisternally injected alpha-2 adenoceptor stimulant clonidine (0.47 nmol/rat) and the delta opioid receptor type agonist (D-Ala(2), D-Leu(5))-enkephalin (0.8 nmol/rat) reduced acidified ethanol-induced mucosal lesions in the stomach by 84.1 and 77.5%, respectively, whereas the same doses were completely ineffective in rats treated neonatally by monosodium glutamate. The data taken together with the results of previous studies with the same substances in rats with retroarcuate knife cuts suggest that neuronal damage in the nucleus of the solitary tract region rather than in the arcuate nucleus is responsible for the changes seen in the pharmacological responsiveness.

Characterization of kappa and delta opioid receptors in isolated organs by using type/subtype selective agonists and antagonists.

BACKGROUND: The kappa and delta opioid receptors were characterized in longitudinal muscle strip of guinea-pig ileum (GPI, mu, kappa), mouse (MVD, delta, mu, kappa) and rabbit (LVD, kappa) vas deferens and rabbit ear artery (ART, delta, kappa) with particular attention to the presence of receptor subtypes. MATERIAL AND METHODS: For this purpose, type/subtype selective agonist and antagonist were used such as [D-Ala2, D-Leu5]-enkephalin (delta agonist) [D-Pen2,5]-enkephalin (delta 1 agonist), deltorphin II (delta 2 agonist) naltriben (NTB, delta 2 antagonist), BOC-YPGFLT(OtBu) (delta antagonist) on the one hand and ethylketocyclazocine (EKC, kappa/(agonist), PD-117 302 (kappa 1 agonist), [Met5]-enkephalin-Arg6, Phe7 (ME-RF, delta/kappa 2/(agonist) and its amide ME-RF-NH2, kappa 2/(agonist), naltrexone (NTX, mu > delta = kappa antagonist) and norbinaltorphimine (nBNI, kappa antagonist) on the other hand. RESULTS AND CONCLUSION: In MVD the Ke of NTB against different (agonists revealed no receptor type heterogeneity. In LVD the Ke of nBNI but not of NTX against EKC versus the ones against ME-RF and ME-RF-NH2 indicated inhomogenous (receptor population. The (receptor antagonist BOC-YPGFLT(OtBu) antagonized the action of ME-RF-NH2 in ART but not in MVD or LVD indicating a special receptor subtype in ART (kappa, possibly delta).

Receptor constants for endomorphin-1 and endomorphin-1-ol indicate differences in efficacy and receptor occupancy.

The opioid properties of endomorphin derivatives containing a C-terminal alcoholic(-ol) function were compared to the parent amidated compounds in isolated organs (longitudinal muscle strip of guinea-pig ileum and mouse vas deferens). Similar data were also generated for the mu-opioid receptor selective agonist synthetic peptide (D-Ala2, MePhe4, Gly5-ol)-enkephalin (DAMGO) and its Gly5-NH2 congener (DAMGA). Endomorphin-1-ol (Tyr-Pro-Trp-Phe-ol) had an IC50 of 80.6 nM in mouse vas deferens and 61.2 nM in guinea-pig ileum; the corresponding values for endomorphin-2-ol (Tyr-Pro-Phe-Phe-ol) were 49.6 and 48.2 nM, for DAMGO 59.8 and 29.2 nM, respectively. As it was indicated by the antagonism by naltrexone, the agonist actions were exerted exclusively at mu-opioid receptors in both organs. The -ol derivatives were slightly (2.3-4.3 times) less potent than the parent amides in the bioassays: all peptides had, apparently, full agonist properties in intact preparations. With the aim of revealing potential partial agonist properties among the investigated peptides, we partially inactivated the mu-opioid receptor pool in mouse vas deferens by 5x10(-7) M beta-funaltrexamine. The calculated receptor constants indicated a "high-affinity, low intrinsic efficacy" profile (i.e. a potential partial agonist property) for endomorphin-1, an intermediate character for endomorpin-1-ol and full agonism for DAMGA and DAMGO. Apparently, a higher receptor fraction remained accessible for endomorphin-1 (42.8%) than for the -ol congener (14.0%), DAMGO (20.2%) and DAMGA (14.1%) after partial inactivation.

Supraspinal delta- and mu-opioid receptors mediate gastric mucosal protection in the rat.

This study evaluated the contribution of supraspinal opioid receptors to gastric mucosal protection in the rat. Intracerebroventricular (i.c.v.) and intracisternal (i.c.) injections of selective delta- [[D-Ala(2),D-Leu(5)]-enkephalin (DADLE), [D-Pen(2),D-Pen(5)]-enkephalin (DPDPE), deltorphin II], selective mu- [[D-Ala(2),Phe(4),Gly(5)-ol]-enkephalin (DAGO)] opioid receptor agonists and beta-endorphin (ligand of both receptor types) produced a dose-dependent inhibition of acidified ethanol-induced gastric mucosal damage. The ED(50) values for beta-endorphin, DAGO, DADLE, deltorphin II, and DPDPE were 3.5, 6.8, 75, 120, and 1100 pmol/rat, respectively, following i.c.v. and 0.8, 9.0, 45, 0.25, and 7 pmol/rat following i.c. injection. The gastroprotective effect of DADLE, deltorphin II, and DPDPE, but not that of DAGO, was inhibited by naltrindole, the selective delta-receptor antagonist. Since the delta(2)-receptor agonist deltorphin II was more potent than the delta(1)-receptor agonist DPDPE, the dominant role of central delta(2)-receptors in gastroprotection might be raised. The site of action for delta-receptor agonists is likely to be the brain stem since the peptides were more potent following i.c. than following i.c.v. administration. The gastroprotective effect was reduced following acute bilateral cervical vagotomy. Moreover, both the nitric-oxide synthase inhibitor N(G)-nitro-L-arginine (3 mg/kg i.v.) and the prostaglandin synthesis inhibitor indomethacin (20 mg/kg p.o.) decreased the protective effect of opioid peptides. The results indicate that 1) activation of supraspinal delta- and mu-opioid receptors induces gastric mucosal protection, 2) integrity of vagal nerve is necessary for the gastroprotective action of opioids, and 3) mucosal nitric oxide and prostaglandins may be involved in the opioid-induced gastroprotection.

[Lethal complication of an odontogenic infection developing after tooth extraction in a patient with untreated diabetes. Case report]. / Odontogén fertózés foghúzás után kialakult halálos szövódménye egy kezeletlen diabeteses betegben (Esetismertetés).

The extraction of a tooth led to the acute exacerbation of existing chronic osteomyelitis then phlegmon, and sepsis as a result. Persisting coma developed after three reanimations of the patient, on account of septic shock. Finally, in more than two weeks following the extraction the patient died due to multiorgan failure. This case description wishes to call attention to the risks of complications of diabetes, to summarize the relevant documents of diagnosis and treatment of osteomyelitis and phlegmon and the data of mortality. Hopefully we offer some useful advice to the general dentist about patients with immunosuppressive diseases.

Alpha-2 adrenergic and opioid receptor-mediated gastroprotection.

Clonidine inhibited the development of gastric mucosal lesions induced by either acidified ethanol or indomethacin. The ED50 values were: 7.1 and 5.2 microg x kg(-1) orally, respectively. The gastroprotective effect was antagonised by the pre-synaptic alpha-2 antagonist yohimbine, the more selective alpha-2 antagonist Ch-38083 and the pre-synaptic alpha-2B antagonist prazosin. Moreover, the non-selective opioid receptor antagonist naloxone, the delta receptor selective naltrindole also reversed the clonidine-induced mucosal protective action. Clonidine was also effective following intracerebroventricular administration with the ED50 of 37 ng/rat against ethanol-induced mucosal damage. Our results suggest that: 1) the gastroprotective effect of clonidine is likely to be mediated by alpha-2B adrenoceptor subtype; 2) there is an interaction between pre-synaptic alpha-2 adrenoceptors and opioid system; and 3) clonidine can induce gastroprotection by central mechanism.

Modulation by GABA(B) and delta opioid receptors of neurally induced responses in isolated guinea-pig taenia coli and human colonic circular muscle.

The GABA-ergic and opioid modulation of neurally induced muscle responses was studied in isolated guinea-pig taenia coli and human colonic circular muscle, using identical field stimulation parameters (rectangular pulses of 0.5 ms duration, 9 V x cm(-1) intensity, trains of 3 pulses at 0.5 Hz, repeated every 1/3/5 min). The stimulation-induced contractions were inhibited in both preparations by GABA and baclofen; the IC50 values in human colonic circular muscle were approximately 100 and 31.0 microM, respectively. In guinea-pig taenia coli, the inhibition by 10(-4) M GABA was dose-dependently reversed by 10(-4)-10(-3) M of GABA(B) receptor antagonist CGP 35348; antagonism by phaclofen was less effective in the same concentration range. In human colonic circular muscle, inhibition by 3 x 10(-5) M baclofen was fully reversed by 10(-3) M CGP 35348. With the exception of caecum, the delta 2 opioid receptor agonist deltorphin II was a potent inhibitor in human colonic circular muscle. 10(-8) M Deltorphin caused a 74.4 +/- 9.6% (n = 4) inhibition which was reversed by 10(-6) M of delta receptor selective peptide antagonist BOC-Tyr-Pro-Gly-Phe-Leu-Thr(OtBu). Deltorphin II was ineffective in guinea-pig taenia coli even at 10(-6) M; the same concentration caused an 84.3 +/- 7.9 (n = 4) inhibition in human preparations. It is concluded that: 1) GABA-ergic modulatory mechanisms are present both in human colonic circular muscle and guinea-pig taenia coli; 2) the GABA receptors involved are of type B; and 3) delta opioid receptor-mediated modulation functions only in human colonic circular muscle in regions other than the caecum.

Functional evidence that gastroprotection can be induced by activation of central alpha(2B)-adrenoceptor subtypes in the rat.

Clonidine injected intracerebroventricularly (i.c.v.) (0.47 nmol/rat) exerted gastric mucosal protective effect against acidified ethanol. Evidence was obtained that the gastroprotective effect of clonidine was blocked by i.c.v. injected alpha(2)-adrenoceptor antagonists yohimbine (non-subtype selective antagonist), prazosin and 2-[2-(4-(O-methoxyphenyl)piperazin-1-yl)ethyl]-4,4-dimethyl-1,3-(2 H, 4H)-isoquinolindione (ARC-239) (representative alpha(2B/2C)-adrenoceptor blocking agents) and opioid receptor antagonists naloxone (a non-selective, moderately mu-opioid receptor preferring antagonist), naltrindole and naltriben delta-opioid receptor antagonists). The centrally injected naltrindole (0.5 nmol/rat) antagonised also the gastroprotective effect of clonidine --but not that of the delta-agonist [D-Ala(2), D-Leu(5)]enkephalin--administered peripherally. The results suggest that central alpha(2B/2C)-adrenoceptor subtypes and opioid--particularly delta--receptors are likely to be involved in the gastric mucosal protective effect of clonidine.

Intracerebroventricular injection of clonidine releases beta-endorphin to induce mucosal protection in the rat.

The possibility that the endogenous opioid system could be involved in the central nervous system (CNS)-mediated gastroprotective effect of clonidine was investigated. Intracerebroventricularly (i.c.v.) injected clonidine (470 pmol/rat) inhibited the gastric mucosal lesions induced by (orally administered) acidified ethanol in a significant manner in the rat. The gastroprotective effect of the centrally administered clonidine was antagonised by i.c.v. or intracisternally (i.c.) administered presynaptic alpha-2 adrenoceptor antagonist, yohimbine; the non-selective opioid receptor antagonist, naloxone; and the delta opioid receptor antagonist naltrindole. These results suggest that an interaction between central alpha-2 adrenoceptors and endogenous opioid systems is involved in mediating the mucosal protective effect. beta-endorphin antiserum (i.c.) also antagonised the gastroprotection induced by intracerebroventricularly injected clonidine indicating that beta-endorphin release is likely to be a key factor in the gastroprotective effect of clonidine. Furthermore, the i.c.v. or i.c. injection of beta-endorphin produced a potent gastroprotection in the picomolar range. The mucosal protective effect of clonidine was abolished after vagotomy indicating that the central effect may be conveyed to the periphery by vagal efferents. Since atropine (1 mg/kg i.v.) failed to modify, but hexamethonium (10 mg/kg i.v.) antagonised the gastroprotective effect of clonidine, it would appear that in the periphery nicotinic, but not muscarinic, cholinergic receptors are likely to be involved in the mucosal protective effect of clonidine. In conclusion, clonidine (i.c.v.) induces gastroprotective action by releasing an endogenous opioid substance - most likely beta-endorphin - in the rat. The clonidine-induced central gastroprotection requires the integrity of vagal pathway; cholinergic nicotinic - but not muscarinic - receptors might mediate the effect in the periphery.

Deltorphin II analogues with 6-hydroxy-2-aminotetralin-2-carboxylic acid in position 1.

Two approaches to the design of very active and highly selective delta opioid peptides were used to obtain new deltorphin analogues with altered hydrophobic and stereoelectronic properties. Deltorphin II analogues were synthesized with the substitution of Ile instead of Val at positions 5 and 6 in the address domain and 6-hydroxy-2-aminotetralin-2-carboxylic acid (Hat) instead of Tyr(1) in the message domain. In the radioreceptor-binding studies, in which type-specific tritiated opioid ligands were used, (R)- and (S)-Hat-deltorphins exhibited similar K(i) values, revealing high delta selectivity. The peptides displayed agonist properties in the in vitro bioassay, with IC(50) values in the subnanomolar range in the mouse vas deferens assay and in the micromolar or higher range in the guinea pig ileum assay, again demonstrating a high selectivity toward delta receptors. The agonist property of the new ligands was confirmed by means of [(35)S]GTPgammaS-binding experiments in membranes of the rat frontal cortex.

New opioid affinity labels containing maleoyl moiety.

Opioid receptor binding properties and pharmacological profiles of novel peptides containing maleoyl function were determined in order to develop new affinity labels. Based on the enkephalin structure peptide ligands were synthesized and tested. Both in in vitro receptor binding experiments and pharmacological studies, all ligands showed agonist character with relatively high affinity (Ki values in the nanomolar range) and good to moderate selectivity. Replacement of Gly2 in the enkephalin frame with D-Ala led to higher affinities with a small decrease in selectivity. The longer peptide chains resulted in compounds with high percentage (up to 86%) of irreversible binding. The selectivity pattern of the ligands is in good agreement with the data obtained from the pharmacological assays (guinea pig ileum and mouse vas deferens bioassays). The newly synthesized peptides could be used in further studies in order to determine more detailed characteristics of the ligand-receptor interaction.

Irreversible labelling of the opioid receptors by a melphalan-substituted [Met5]enkephalin-Arg-Phe derivative.

[Met5]enkephalin-Arg-Phe (Tyr-Gly-Gly-Phe-Met-Arg-Phe) was modified with the methyl esther of melphalan (Mel; 4-bis(2-chloroethyl)amino-L-phenylalanine) and the resulting compounds were studied for their opioid binding properties in guinea pig and rat brain membranes. Three new peptides, with a substitution of a single amino acid, were synthesized (Mel-Gly-Gly-Phe-Met-Arg-Phe, Tyr-Gly-Gly-Mel-Met-Arg-Phe and Tyr-Gly-Gly-Phe-Met-Arg-Mel). In the rat brain, none of these ligands displayed any type specificity, whereas in guinea pig brain membranes the C-terminally modified peptide, Tyr-Gly-Gly-Phe-Met-Arg-Mel ([Mel7]peptide), displayed a kappa-binding profile and was a weak kappa-opioid-receptor agonist in isolated guinea pig ileum. The effect of sodium ions on [Mel7]peptide competition against [3H]naloxone binding indicated a weak agonist nature of the compound. When guinea pig brain membranes were preincubated with 1-10 microM of [Mel7]peptide, an apparently irreversible inhibition of [3H]naloxone ligand binding was observed. These results suggest that the heptapeptide containing melphalan at the C-terminus can be used as a relatively high-affinity irreversible label for the kappa-opioid receptor.

Diprotin A, an inhibitor of dipeptidyl aminopeptidase IV(EC 3.4.14.5) produces naloxone-reversible analgesia in rats.

The dipeptidyl aminopeptidase IV (DP IV) inhibitor Diprotin A produces a full, dose-dependent, short-lasting and naloxone-reversible analgesia in the rat tail-flick test when given intracerebroventricularly, with an ED50 of 295 nmol/rat but it has no direct opioid agonist activity in the longitudinal muscle strip of guinea-pig ileum bioassay. Two of the potential DP IV substrates, morphiceptin and endomorphin 1, identified recently in bovine brain were also analgesic given by similar route. The action of endomorphin 1 was more potent (ED50 = 7.9 nmol/rat) and slightly but significantly more sustained than that of Diprotin A. Diprotin A neither potentiated nor prolonged the effect of a marginally analgesic dose of endomorphin 1. The distinct time course and the lack of potentiation indicate that in the analgesic effect of Diprotin A in rats the protection of a brain Tyr-Pro-peptide other than endomorphin 1 is involved.

Changes in cardiac electrophysiology, morphology, tissue biochemistry and vascular reactions in glutathione depleted animals.

The effects of acute and chronic glutathione depletion (single i.p. injection of 3 mmol/kg L-buthionine-S,R-sulphoximine and 2 mmol/kg for 4 days) on heart action potential (AP) characteristics, electronmicroscopy, cytochemistry and biochemistry and vascular contractility and nitric oxide-mediated relaxation were studied in rats and guinea pigs. In guinea pig cardiac preparations both acute and chronic glutathione depletion caused a significant decrease of maximum rate of rise of depolarization phase and duration of action potential AP(APD) at 25, 50, and 90% of repolarization but did not modify the other AP parameters. The contractile responses of helically cut aortic strips to norepinephrine were not altered by chronic glutathione depletion but the relaxing responses of precontracted preparations to acetylcholine were significantly reduced both in rats and guinea pigs. Morphologically there were indications of permeability changes, intracellular and interstitial edema and myofilament damage in the myocardium. There was also a decrease in cytochromoxydase and succinyl dehydrogenase activities both in rats and guinea pigs. The present data suggest that glutathione depletion may influence the Na+ and K+ channel activities, causes morphological and biochemical changes in cardiac preparations and may interfere with nitric oxide generation or its action in aortic strips.

Clinical implication of screening p53 gene mutations in head and neck squamous cell carcinomas.

The role of the tumour-suppressor gene p53 in the tumorigenesis of head and neck cancer has been well established, but the clinical significance of p53 alteration is still unclear. A group of 50 patients with head and neck squamous cell carcinoma (HNSCC) were investigated for p53 alterations. DNA was extracted from fresh tumour samples and polymerase chain reaction/single-strand conformation polymorphism analysis was used to detect p53 gene mutations in the region from exon 5 to exon 9. In addition, p53 protein overexpression was assessed by immunohistochemistry using the monoclonal antibody DO-7 on paraffin-embedded tissue sections. p53 gene mutations were found in 45% and p53 protein expression was detected in 61.2% of tumour samples. While p53 protein expression was not correlated with any clinical factors, p53 gene mutations indicated local regional recurrences of HNSCC. The risk of locoregional recurrence was significantly greater in patients with a p53 gene mutation than in patients with the wild-type p53 gene (P = 0.001). Multivariate analysis confirmed p53 gene mutation to be an independently predictive factor for the tumour recurrence (P = 0.0064). When we analysed p53 gene mutation in 12 patients with primary and recurrent tumours, we found that 4 patients (33.3%) had a different p53 gene mutation in the recurrent tumour from that in the original primary tumour. The results indicate that p53 gene mutations and not protein overexpression are valuable predictors for tumour recurrences and for differential diagnosis of a second primary HNSCC.

Affinity profiles of novel delta-receptor selective benzofuran derivatives of non-peptide opioids.

Highly selective heterocyclic opioid ligands with potent delta-antagonist activity have been developed on the basis of the "message-address" concept. Using this strategy, benzofuran derivatives corresponding to the non-selective opioid antagonist, naloxone, and to the mu-opioid receptor selective agonists, oxymorphone and oxycodone, were synthesized. In vitro opioid receptor binding profiles and agonist/antagonist character of these compounds were determined in rat brain membrane preparations with highly selective radioligands. All three benzofuran derivatives displayed high affinities for the delta-opioid receptor, much less potency toward the mu-binding site, and were the least effective at the kappa-site. The results indicated that the addition of the bezofuran moiety to these fused ring opioids confers delta-receptor selectivity. The Na+ indices suggested a partial agonist character for oxymorphone- and oxycodone-benzofuran, and an antagonist character for naloxone-benzofuran. These compounds were capable of irreversible inhibition of opioid binding sites in a dose-dependent.

Analysis of the role of delta opioid receptors in gastroprotection in the rat.

The effect of delta opioid agonists - [D-Ala2, D-Leu5]-enkephalin (DADLE), [D-Pen2, D-Pen5]-enkephalin (DPDPE) and deltorphin II - on acidified ethanol induced gastric mucosal lesions was studied in the rat compared with that of morphine. It was found that DADLE, DPDPE, deltorphin II and morphine exerted a dose-dependent inhibition on the mucosal lesions injected subcutaneously, their ID50 values were 0.037, 1.8, 3.5 and 0.35 micromoles/kg, respectively. Naltrindole (10 mg/kg sc.), the selective delta opioid receptor antagonist, inhibited the gastroprotective effect of DADLE, DPDPE and deltorphin II, but it failed to antagonise the effect of morphine. Our results suggest that 1. delta receptors are involved in opioid-mediated gastroprotection, 2. ethanol-induced gastric mucosal damage in the rat may be a quick, simple in vivo model for screening opioid delta receptor agonists and antagonists in the periphery.