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The aim of the present study was to analyze whether angiotensin II via the endocannabinoid system can induce gastric mucosal protection, since transactivation of cannabinoid CB1 receptors by angiotensin AT1 receptor in CHO cells was described. Experimental ulcer was induced by acidified ethanol given orally in male Wistar rats, CB1(+/+) wild type and CB1(-/-) knockout mice. The compounds were administered intracerebroventricularly. It was found, that 1. Angiotensin II inhibited the ethanol-induced gastric lesions (11.9-191pmol); the effect of angiotensin II (191pmol) was inhibited by the CB1 receptor inverse agonist AM 251 (1.8nmol) and the inhibitor of diacylglycerol lipase (DAGL), tetrahydrolipstatin (0.2nmol). 2. Angiotensin II exerted gastroprotection in wild type, but not in CB1(-/-) mice. 3. The gastroprotective effect of angiotensin II (191pmol) was reduced by atropine (1mg/kg i.v.) and bilateral cervical vagotomy. In conclusion, stimulation of central angiotensin AT1 receptors via activation of cannabinoid CB1 receptors induces gastroprotection in a DAGL-dependent and vagus-mediated mechanism., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

We have reported previously that the dipeptidyl peptidase IV inhibitor Ile-Pro-Ile had an antihyperalgesic action in rats when given intrathecally in the carrageenan-induced hyperalgesia, as detected by the Randall-Selitto test. Vildagliptin, a non-peptide inhibitor of the same enzyme, which is already on the market as an "euglycemic" agent in diabetics, has a slightly more potent and more sustained antihyperalgesic effect in the same test when given by the same route. The action of 3nmol/rat vildagliptin could be antagonized by subcutaneous naltrexone (0.5mg/kg) pretreatment, or by intrathecally co-administered specific antiserum to endomorphin-2. Thus, the antihyperalgesia by vildagliptin, similarly to Ile-Pro-Ile, was opioid receptor-mediated and could be attributed to the promotion of endomorphin-2 generation in rat spinal cord dorsal horn. Furthermore, vildagliptin (1mg/kg) is a potent antihyperalgesic also when given subcutaneously., (Copyright © 2010. Published by Elsevier B.V.)

We have found recently that membrane-bound dipeptidyl peptidase IV (DPP-IV) generated extracellularly immunoreactive endomorphin-2 from Tyr-Pro precursor in a depolarisation-sensitive manner in rat isolated L4,5 dorsal root ganglia when the enzyme was switched to synthase mode by the hydrolase inhibitor Ile-Pro-Ile. Presently, we induced hyperalgesia in rats by injecting carrageenan into the right hindpaw and measured the reduction in nociceptive threshold (hyperalgesia) to pressure (Randall-Selitto test). The hyperalgesia, peaking at 180 min after injection, was fully reversed by intrathecal administration of 30 nmol/rat Ile-Pro-Ile. The antihyperalgesic action was antagonized by s.c. naloxone (1 mg/kg) and intrathecally injected specific antiserum to endomorphin-2 indicating that the opioid receptor-mediated effect was produced by an endogenously generated endomorphin-2-like immunoreactive substance. Intrathecal Ile-Pro-Ile was ineffective as an analgesic in the acute nociceptive test such as the rat tail-flick, whereas endomorphin-2 (EC(50)=13.3 nmol/rat), endomorphin-1 (6.8 nmol/rat), morphine (0.11 nmol/rat) and DAMGO (0.0059 nmol/rat) exerted opioid receptor-mediated analgesia given by the same route. We concluded that carrageenan-induced C-fiber barrage (wind-up) may create ideal conditions for the de novo synthesis of endomorphin-2 in rat spinal cord dorsal horns if the DPP-IV enzyme is switched to the synthase functional mode by Ile-Pro-Ile.

Background and Aims: The gene(s) encoding for endomorphin precursor(s) is/are still unknown. We have raised the possibility of and did find some evidence for a potential de novo biosynthetic route starting from Tyr-Pro precursor. To pursue further this possibility we measured the generation of immunoreactive endomorphin-2 (E2-IR) in adult rat isolated L4,5 dorsal root ganglia., Results and Conclusions: In rat isolated dorsal root ganglia the combination of presumed biosynthetic precursor of endomorphin 2 (E2), Tyr-Pro with the dipeptidyl peptidase IV (DPP-IV) inhibitor Ile-Pro-Ile generated 1.60+/-0.37 pg/mg Wet Tissue Weight_30 min E2-IR in the bathing fluid (n=4) with an 8-fold increase upon depolarization whereas the tissue content was low (0.50+/-0.08 pg/mg_WTW). Substance P, as determined by ELISA in the pilot experiments, was found almost exclusively within the tissues. It is concluded that E2-IR was generated extracellularly by a membrane-bound DPP-IV, which was switched to "synthase" mode by the hydrolase inhibitor Ile-Pro-Ile. DPP-IV was depolarization-sensitive in "synthase" functional mode.

To pursue further the possible de novo biosynthetic pathway of endomorphins in rat brain we raised antibodies to endomorphin-2 conjugate in rabbits. Antiserum R1 recognized endomorphin-2 with good selectivity as compared to endomorphin-1 with a median detection value of 65.5+/-7.5 pg/tube (n=7), whereas R4 antiserum recognized both endomorphins with similar sensitivity. Neither antisera recognized YP-related di- or tripeptides or YGGF-related opioid sequences (enkephalins, beta-endorphin, dynorphin). Using the same rat brain extraction-RP-HPLC-gradient separation paradigm as previously, antisera detected 144.6+/-40.0 (n=3) pg/g wet brain weight endomorphin-2-like immunoreactivity in the fraction corresponding to standard endomorphin-2 retention time and also in the fraction matching endomorphin-2-OH standard retention time (179.1+/-30.1 pg/g). Since R1 failed to recognize authentic endomorphin-2-OH, the second immunoreactive species must be different from both endomorphin-2 and endomorphin-2-OH. Possible biosynthetic intermediates to endomorphins, synthetic YPFFG and YPWFG had retention times close to the parent endomorphin standards in RP-HPLC gradient separation profile. The former was a mu-opioid receptor agonist of medium potency in the in vitro assays (rat brain RBA&GTP gamma S binding and mouse vas deferens), whereas the latter was a weak mu-opioid receptor agonist with a significant delta-opioid receptorial action as well and a definite indication of partial agonism.

We sought an isolated vascular preparation and experimental setting where the function of alpha2B-adrenoceptors could be demonstrated by non-recombinant technique. ST-91 (2-[2,6-diethylphenylamino]-2-imidazoline), an alpha 2B-adrenoceptor agonist with a mixed alpha adrenergic receptor type/subtype selection profile antagonized the relaxant effect of isoproterenol in endothelium-denuded rat mesenteric artery rings precontracted with phenylephrine. At 10(-7) M of ST-91, the antagonism was characterized by a rightward shift of isoproterenol dose-response curve (A50=6.81+/-1.40 e-7 (n=4) vs the control 1.29+/-0.25 e-7 M (n=4)) with no E(max) depression. At 10(-6) M the Emax depression was prevalent (36.1+/-7.0% (n=4) vs the control 79.9+/-5.1% (n=4)); both actions could be antagonized by the alpha2-adrenoceptor antagonist yohimbine. The not subtype-selective alpha(2)-adrenoceptor agonist xylazine (10(-7) M) did not affect the relaxant action of isoproterenol. Present findings are discussed in the light of previously reported hemodynamic effects attributed to alpha2B-adrenoceptors in receptor subtype-knockout animals.

Nociceptin, a 17-amino acid peptide (FGGFTGARKSARKLANQ, N/OFQ), is the endogenous ligand of the nociceptin/orphanin FQ (NOP) receptor. This receptor-ligand system is involved in various physiological as well as pathophysiological mechanisms, but owing to the peptidic structure, it is rapidly degraded by enzymes. The enzymatic digestion of nociceptin involves mainly aminopeptidases and yields Noc(2-17)-OH and other smaller fragments. We aimed at increasing the enzymatic stability against aminopeptidases in the case of peptide Noc(1-13)-NH(2), which possesses the minimum sequence capable of interacting with the NOP receptor. Therefore we developed a new procedure for the synthesis of peptides with the carbamic acid residue [...-NH-CH(R)-CO-NH-CO-NH-CH(Q)-CO-.]. A set of four carbamic acid-nociceptin derivatives were produced. The carbamic acid residue was incorporated into the inner part of the peptides, building on solid phase, by using a suitable dipeptide fragment with carbamic acid residue produced by a simple and efficient three-step solution phase procedure. Enzymatic stability of carbamic acid peptides was studied in the presence of aminopeptidase M (AP-M) and in rat brain membrane homogenate. The receptor-binding properties were also studied by radioligand binding assay on crude rat brain membranes and the activity of the ligands were analyzed on isolated mouse vas deferens (MVD) tissues. We found that incorporation of the carbamic acid residue into the N-terminal part of nociceptin significantly increases the resistance against AP-M. We observed the decrease of binding affinities to the NOP receptor in case of the peptides modified in the N-terminal portion. Consequently, the incorporation of the carbamic acid residue into peptides can be proposed as a promising and reasonable tool for increasing enzymatic stability, where the native molecule is less sensitive for carbamic acid residue-related structural change.

The partial mu-opioid receptor pool inactivation strategy in isolated mouse vas deferens was used to determine partial agonism of endomorphins and their analogs (endomorphin-1-ol, 2',6'-dimethyltyrosine (Dmt)-endomorphin-1, endomorphin-2-ol and (D-Met2)-endomorphin-2) using morphine, normorphine, morphiceptin, (D-Ala2,MePhe4,Gly5-ol)-enkephalin (DAMGO) and its amide (DAMGA) as reference opioid agonists. Agonist affinities (KA) and efficacies were assessed both by the "null" and the "operational" method. The KA values determined by the two methods correlated significantly with each other and also with the displacing potencies against 3H-naloxone in the receptor binding assay in the presence of Na+. DAMGO and DAMGA were full agonist prototypes, morphine, endomorphin-1, endomorphin-1-ol, Dmt-endomorphin-1, endomorphin-2-ol and (D-Met2)-endomorphin-2 were found by both methods to be partial agonists whereas the parameters for normorphine, morphiceptin and endomorphin-2 were intermediate.

In spite of concentrated efforts, the biosynthetic route of mu-opioid receptor agonist brain tetrapeptide endomorphins (Tyr-Pro-Trp-Phe-NH2 and Tyr-Pro-Phe-Phe-NH2), discovered in 1997, is still obscure. We report presently that 30 min after intracerebroventricular injection of 20 or 200 microCi [3H]Tyr-Pro (49.9 Ci mmol(-1)) the incorporated radioactivity was found in endomorphin-related tetra- and tripeptides in rat brain extracts. As detected by the combination of HPLC with radiodetection, a peak corresponding to endomorphin-2-OH could be identified in two of four extracts of "20 microCi" series. Radioactive peaks in position of Tyr, Tyr-Pro, Tyr-Pro-Phe or Tyr-Pro-Trp appeared regularly in both series and also in the "tetrapeptide cluster" constituted by endomorphins and their free carboxylic forms. In one of the four extracts in the "200 microCi" series a robust active peak in the position of endomorphin 2 could be detected. Intracerebroventricularly injected 100 nmol, but not 10 or 1000 nmol cold Tyr-Pro (devoid of opioid activity in vitro), caused a naloxone-reversible prolongation of tail-flick latency in rats, peaking between 15 and 30 min. We suggest that Tyr-Pro may serve as a biosynthetic precursor to endomorphin synthesis.

The effect of clonidine on ethanol-induced gastric mucosal damage, gastric emptying and gastric motility was compared. The clonidine-induced gastroprotective effect (0.03-0.09 micromol/kg, s.c.) was antagonised by yohimbine (5 micromol/kg, s.c.), prazosin (0.23 micromol/kg; alpha2B-adrenoceptor antagonist) and naloxone (1.3 micromol/kg, s.c.). Clonidine also inhibited the gastric emptying of liquid meal (0.75-3.75 micromol/kg, s.c.) and gastric motor activity (0.75 micromol/kg, i.v.) stimulated by 2-deoxy-D-glucose (300 mg/kg, i.v.). Inhibition of gastric emptying and motility was reversed by yohimbine (5 and 10 micromol/kg, s.c., respectively), but not by prazosin (0.23 micromol/kg, s.c.) or naloxone (1.3 micromol/kg, s.c.). Oxymetazoline-an alpha2A-adrenoceptor agonist-inhibited both gastric emptying (0.67-6.8 micromol/kg, s.c.) and motility (0.185-3.4 micromol/kg, i.v.), whereas it failed to affect gastric mucosal lesions. The results indicate that in contrast to the gastroprotective effect, which is mediated by alpha2B-adrenoceptor subtype, alpha2A-adrenoceptor subtype may be responsible for inhibition of gastric emptying and motility. However, the site of action (central, peripheral, both) remains to be established.

Nociceptin is an endogenous anti-opiate heptadecapeptide primarily interacting with the nociceptin (NOP) receptor. This neuropeptide-receptor system is involved in pain regulation, tolerance to and dependence on opiates as well as many other physiological and pathophysiological events. The role and mechanisms of nociceptin in pathological conditions is not clearly known yet. In an attempt to have a radiopharmaceutical labeled either with 99mTc or (111)In, we incorporated diethylenetriaminepentaacetic acid (DTPA) as chelator into the structure of [Arg14,Lys15]nociceptin(1-17)-NH2 at the epsilon-amino group of Lys15. Such a radiopeptide may be useful in imaging for diagnostical purposes. Preparation of the peptide ligands was carried out by solid phase synthesis. Two peptides containing DTPA were obtained and purified. The products were [Arg14,Lys(DTPA)15]nociceptin(1-17)-NH2 and its cross-linked dimer on the basis of mass spectrometric analysis. In (115)In3+ binding experiments the conjugates exhibited preserved indium ion chelating properties, indicating the potential use of radiolabeled DTPA-nociceptin derivatives as radiopharmaceutical. Biological properties of these compounds were studied in rat brain membrane preparations by radioligand binding, functional biochemical [35S]GTPgammaS binding assays and mouse vas deferens (MVD) bioassay. Besides the similar in vitro binding characteristics to nociceptin receptor, both of the DTPA-chelated compounds were more potent and efficient than nociceptin in functional biochemical and mouse vas deferens bioassays. Our further aim is to radiolabel these compounds in order to get a radiopharmaceutical which can be used diagnostically.

In search for effective antagonist structures for the nociceptin (NOP) receptor, a number of N-acylated oligopeptides, including N-acyl tetra- and pentapeptides selective for the kappa-opioid receptor, as well as N-acyl hexapeptides bearing the Ac-Arg-Tyr-Tyr-Arg-Ile-Lys (Ac-RYYRIK) core sequence originally isolated from combinatorial chemical libraries, were synthesized and studied in radioreceptor binding assays, [(35)S]GTPgammaS functional tests and in mouse vas deferens (MVD) bioassays. The properties of the novel antagonist candidates were compared to known antagonists. A new antagonist structure with a reduced, primer alcohol C-terminus, Ac-Arg-Tyr-Tyr-Arg-Ile-lysinol (Ac-RYYRIK-ol) was described in the mouse vas deferens tests, showing an equilibrium inhibitory constant value (K(e)) of 2.44 nM, and no agonist effect at 10 microM ligand concentration. Schild-analysis indicated a clearly competitive interaction at the NOP receptor, whereas the peptide did not affect the action of the delta-opioid receptor agonist [D-Ala(2),D-Leu(5)]enkephalin. Ac-RYYRIK-ol also exhibited a high affinity in [(3)H]nociceptin-NH(2) binding competition assays using rat brain membranes. Agonist-induced G-protein activation via NOP receptors was studied in [(35)S]GTPgammaS binding stimulation assays by the use of both native brain tissue preparations and membranes from cultured CHO cells expressing recombinant nociceptin receptors. Ac-RYYRIK-ol displayed only weak intrinsic agonist activity, whereas it effectively inhibited the stimulation generated by nociceptin. The results support the high potency and antagonist nature of Ac-RYYRIK-ol and reveal important roles for both the N- and the C-terminal region of the molecule.

In nucleus tractus solitarii-dorsal vagal nucleus slices prepared from young adult rats (180-260 g) 10(-3) M L-glutamate and 10(-5) M baclofen caused a 2-3-fold increase of field stimulation-induced [3H]-norepinephrine release without affecting the resting release. In slices prepared from rats treated neonatally with monosodium glutamate neither L-glutamate nor baclofen had any effect on stimulation-induced norepinephrine release, tested between postnatal days 74-99 (350-530 g). In untreated littermates used in the same period (460-580 g) L-glutamate was fully effective whereas baclofen was ineffective. The tritium content in tissue extracts did not differ significantly in the three experimental groups. It is concluded that i) the loss of GABA(B) receptor-mediated disinhibitory stimulation of norepinephrine release is an age-related phenomenon and ii) neonatal monosodium glutamate treatment causes a damage in the local neural circuitry characterized by the loss of glutamate receptor-mediated mechanism that stimulates the release of norepinephrine.

Endomorphins-1 and -2 were substituted with all the beta-MePhe stereoisomers in their Phe residues to generate a conformationally constrained peptide set. This series of molecules was subjected to biological assays, and for beta-MePhe(4)-endomorphins-2, a conformational analysis was performed. Incorporation of (2S,3S)-beta-MePhe(4) resulted in the most potent analogues of both endomorphins with enhanced enzymatic stability. Their micro opioid affinities were 4-times higher than the parent peptides, they stimulated [(35)S]GTPgammaS binding, and they were found to be full agonists. NMR experiments revealed that C-terminal (2S,3S)-beta-MePhe in endomorphin-2 strongly favored the gauche (-) spatial orientation which implies the presence of the chi(1) = -60 degrees rotamer of Phe(4) in the binding conformer of endomorphins. Our results emphasize that the appropriate orientation of the C-terminal aromatic side chain of endomorphins is substantial for binding to the micro opioid receptor.

We used two, 3-min field stimulation cycles 30 min apart (S1, S2) in 3H-norepinephrine-loaded, superfused rat nucleus tractus solitarii-dorsal motor vagal nucleus (NTS-DVN) slices. The stimulation-induced release was expressed as the area above the baseline. Drugs were introduced 12 min before S2 and drug actions were characterized in terms of alterations of S2/S1 ratios. The S2/S1 ratio was 1.047 (0.946-1.159, n = 4, geometric mean and 95% confidence interval) in controls and 0.336 (0.230-0.490, n = 3), 0.726 (0.590-0.892, n = 4), 0.613 (0.594-0.683, n = 4) and 0.665 (0.500-0.886, n = 4) in the presence of 10(-6) M clonidine, D-Ala(2),MePhe(4),Gly(5)-ol-enkephalin (DAMGO), endomorphin-1 (Tyr-Pro-Trp-Phe-NH(2), EM-1) and -2 (Tyr-Pro-Phe-Phe-NH(2), EM-2) [the latter two in the presence of 10(-4) M diprotin A, an inhibitor of dipeptidyl-aminopeptidase IV (DAP-IV) enzyme]. The effect of DAMGO at 10(-5) M was significantly higher than at 10(-6) M, whereas the effect of endomorphins did not differ at the two concentration levels. Diprotin A potentiated only very modestly the action of endomorphins. These data (a) confirm the presence of functional mu-opioid receptors in the vagal complex, (b) render it likely that the enzymic degradation of endomorphins is not a highly effective process in brain slices and (c) may suggest that the apparent ceiling in the effect of endomorphins might be related to their partial agonist property., (Copyright 2002 Elsevier Science B.V.)

Previously, using the acidified ethanol-induced ulcer model in rats, we demonstrated that the mainly vagus-dependent gastroprotective effect of intracerebroventricularly injected clonidine was mediated by beta-endorphin release in the lower brainstem. Presently, retroarcuate transections were used to evaluate the contribution of forebrain beta-endorphinergic projection in this mechanism. Since the transection trajectory affected the cingulate cortex and other forebrain structures, matching lesions were also performed. In control and sham-operated rats intracisternal injection of clonidine and the direct opioid receptor (delta type) stimulant peptide (D-Ala(2), D-Leu(5))-enkephalin caused a potent and fully naloxone-reversible (i.e. opioid receptor-mediated) protection against acidified ethanol-induced mucosal damage. In gyrus cinguli-transected rats (as well as in groups with midline hippocampal, thalamic and hypothalamic lesions) gastric mucosal protection induced centrally by direct delta-opioid receptor stimulation in the lower brainstem was completely abolished. The protective effect of clonidine was significantly reduced but it was still present in these animals. The residual protection by clonidine was naloxone-resistant, i.e. independent of an opioid mediation. Transections of the cingulate gyrus as well as thalamic but not the retroarcuate transections elevated plasma corticosterone levels. The changes seen in the clonidine/opioid-induced gastroprotection did not show any correlation with the changes in plasma corticosterone levels. It was concluded that (i) the transection of the cingulate cortex strongly influences the neural input to the nucleus tractus solitarii-dorsal motor vagal nucleus complex that is required for the activation of gastroprotective vagus outflow by delta-opioid receptor stimulation; (ii) the transection uncovers a direct, clonidine-induced gastroprotective pathway which is probably suppressed in intact animals.

The intracerebroventricularly (i.c.v.) injected presynaptic alpha2-adrenoceptor agonists, clonidine and oxymetazoline, exerted a dose-dependent inhibition on the gastric acid secretion in pylorus-ligated rats; the ED50 values were 20 and 7.5 nmol/rat, respectively. Moreover, beta-endorphin, given i.c.v., also decreased acid secretion (ED50=0.25 nmol/rat i.c.v.). The antisecretory effect of these compounds was highly reduced by glibenclamide (10 nmol/rat i.c.v.), a selective blocker of K(ATP) channels. These results suggest that K(ATP) channels in the central nervous system are likely to be involved in the centrally initiated antisecretory action of both alpha2-adrenoceptor agonists and beta-endorphin.

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.

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.

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).

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 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.

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.

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.

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.

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.

[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.

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.

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.

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.

Hip-Arg-Phe-, Hip-Phe-Arg- and Hip-His-Leu-cleaving dipeptidyl carboxypeptidase activities were measured in the supernatant (S2) and pellet (P2) fractions obtained by ultracentrifugation of human adrenal tumor preparations. Negligible enzyme activity was found in cortical tumor whereas highly significant activities were present in the P2 fractions of the two pheochromocytoma specimens. The hydrolysis rates, expressed in terms of the percent of added substrate were 58-66%/60 min for Hip-Phe-Arg, 55-58%/60 min for Hip-Arg-Phe and 19-30%/60 min for Hip-His-Leu. The angiotensin-converting enzyme inhibitor, captopril, differentially inhibited the enzyme splitting Hip-His-Leu versus the one cleaving Hip-Arg-Phe; Hip-Phe-Arg is probably the substrate of both. It is concluded that the Hip-Arg-Phe-cleaving enzyme in adrenomedullary tumor is probably identical to the purportedly novel dipeptidyl carboxypeptidase that we detected earlier in rabbit ear artery wall, which converts (Met5)-enkephalin-Arg6,Phe7 to (Met5)-enkephalin.

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.

Opioid properties of several morphiceptin- (Tyr-Pro-Phe-Pro-NH2), Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) and dynorphin-derivatives were characterized in rat brain in vitro receptor binding assay and in electrically stimulated longitudinal muscle strip preparation of guinea pig ileum. In the case of morphiceptin-related peptides, an excellent correlation was found between the [3H]-naloxone binding displacement data and the agonist potencies determined in the bioassay. The "turning point' was the C-terminal amidation in the tri- and tetrapeptide pairs in both series. Tyr-MIF-1 derivatives showed weak affinity in the opioid receptor binding assay and none of them had any remarkable effect in the bioassay either as agonist or antagonist. The dynorphin A(1-10)-peptides modified at positions 5 and 8 retained their affinity with Pro5-, Pro8-, and Ala8-substituents, whereas some loss of affinity was observed in the case of Gly8-Dyn A(1-10).

BOC-Tyr-Pro-Gly-Phe-Leu-Thr(OtBu) is a potent, highly delta-opioid receptor-selective competitive antagonist, the Ke values in the mouse vas deferens in vitro assay against [D-Ala2, D-Leu5]-enkephalin [D-Pen2, D-Pen5]enkephalin and deltorphin-II being 39.5, 38.7 and 27.3 nM, respectively, whereas those against [D-Ala2, MePhe4-Gly5-ol]enkephalin (DAMGO) and ethylketocyclazocine in the guinea-pig ileum are 368,000 and > 200,000 nM, giving a higher than 9000-fold delta- vs mu- and a higher than 5000-fold delta- vs kappa-selectivity ratio. The Ki values against various labeled delta-ligands in the rat brain receptor binding assay were in the 300-1000 nM range, whereas the Ki against [3H]-DAMGO was higher than 30,000 nM. The striking discrepancies between bioassay and receptor binding data show another aspect of already recognized differences of mouse vas deferens and rat brain delta-receptors. With the aim of producing a delta-selective affinity ligand, we synthesized the BOC-Mel1 derivative; however, there was a 175-fold loss of delta-receptor affinity in the bioassay and no indication of an irreversible interaction, but a delta-agonist effect appeared in spite of nonprotonated nitrogen. The corresponding BOC-Phe1 derivative had a 10 times higher affinity and, apparently, no agonist activity.

The captopril-inhibited enzyme which forms [Met5]-enkephalin from [Met5]-enkephalin-Arg6,Phe7 in isolated rabbit ear artery was characterized further by using various natural substrate candidates/analogues ([Met5]-enkephalin-Arg6,Phe7 and its amide, [Met5]-enkephalin, angiotensin I and bradykinin), peptidase inhibitors such as captopril, enalaprilate and thiorphan and by endothelial removal. 10(-5) and 10(-4) M but not 10(-6) M captopril reduced the effectiveness of [Met5]-enkephalin-Arg6,Phe7 and potentiated the effect of bradykinin but did not affect markedly the action of the other peptides. Of the inhibitors, enalaprilate was less effective than captopril, and thiorphan had no effect. The [Met5]-enkephalin-Arg6,Phe7-->[Met5]-enkephalin conversion was not affected by endothelial removal. The substrate and inhibitor spectrum of this non-endothelial enzyme activity bears no relationship in other, hitherto characterized dipeptidylcarboxypeptidases/endopeptidases known to be involved in the metabolism of the tested peptides.

Opioid receptor antagonist properties of the mu opioid receptor selective peptide, BOC-Tyr-Lys-Lys-Trp-Trp-NH2 and its systematically modified analogues were determined in guinea pig ileum, mouse vas deferens and rabbit vas deferens bioassays to locate the necessary structural features to develop kappa receptor selective antagonist(s) of substantial affinity. Replacing the tyrosine residue by phenylalanine as well as increasing the lipophilicity of the C-terminal by isoamylamide substitution yielded enhanced kappa receptor affinity. The presence of the C-terminal lipophilic Trp-Trp-NH2 region is necessary as revealed from the equilibrium dissociation constant values. Recognizing that only one lysine residue is required for the antagonist activity led to the synthesis of the tetrapeptide BOC-Tyr-Lys-Trp-Trp-NH2 having a kappa/mu selectivity of 22 and a Ke of 5.4 microM.

To find a delta-opioid receptor preferring peptide structure containing an Asp residue in a potentially interacting position, Tyr-Pro-Phe-Asp, Tyr-D-Ala-Phe-Asp, Tyr-D-Ala-Gly-Phe-Asp, Tyr-D-Ala-Gly-Phe-Asp alpha- and beta-methyl ester and Tyr-Gly-Gly-Phe-Asp peptides were synthesized and their biological activities were analyzed in vitro in mouse vas deferens and longitudinal muscle strip of guinea pig ileum. Changing the beta-methyl ester for an alkylating chloromethyl ketone moiety in the delta-receptor-selective agonist Tyr-D-Ala-Gly-Phe-Asp-beta-methyl ester enhanced further the delta-receptor preference. The delta-receptor selective chloromethyl ketone but not the beta-methyl ester gave a very slow washout after prolonged incubation in the mouse vas deferens bioassay; however, it was still readily displaceable by naloxone. The washout pattern of mu-specific Tyr-D-Ala-Gly-(Me)Phe chloromethyl ketone did not differ in the bioassays from that of the corresponding Gly5-ol derivative. Both chloromethyl ketones gave irreversible characteristics in the receptor binding assay.

Comparative CD and Fourier transform ir (FTIR) spectroscopic data on N-Boc protected linear peptides with or without the (Pro-Gly) beta-turn motif (e.g., Boc-Tyr-Pro-Gly-Phe-Leu-OH and Boc-Tyr-Gly-Pro-Phe-Leu-OH) are reported herein. The CD spectra, reflecting both backbone and aromatic contributions, were not found to be characteristic of the presence of beta-turns. In the amide I region of the FTIR spectra, analyzed by self-deconvolution and curve-fitting methods, the beta-turn band showed up between 1639 and 1633 cm-1 in trifluoroethanol (TFE) but only for models containing the (Pro-Gly) core. This band was also present in the spectra in chloroform but absent in dimethylsulfoxide. These findings, in agreement with recent ir data on cyclic models and 3(10)-helical polypeptides and proteins in D2O [see S. J. Prestrelski, D. M. Byler, and M. P. Thompson (1991), International Journal of Peptide and Protein Research, Vol. 37, pp. 508-512; H. H. Mantsch, A. Perczel, M. Hollósi, and G. D. Fasman (1992), FASEB Journal, Vol. 6, p. A341; H. H. Mantsch, A. Perczel, M. Hollósi, and G. Fasman (1992), Biopolymers, Vol. 33, pp. 201-207; S. M. Miick, G. V. Martinez, W. R. Fiori, A. P. Todd, and G. L. Millhauser (1992), Nature, Vol. 359, pp. 653-655], suggest that the amide I band, with a major contribution from the acceptor C = O of the 1<--4 intramolecular H bond of beta-turns, appears near or below 1640 cm-1, rather than above 1660 cm-1.(ABSTRACT TRUNCATED AT 250 WORDS)

The kinetic parameters of antagonism by the delta opioid receptor selective antagonist N-t-Boc-Tyr-Pro-Gly-Phe-Leu-Thr, obtained by using moderately selective or selective agonists, were compared in the mouse vas deferens bioassay. The apparent affinity for the preferred receptor type was 6.8 times higher when selective agonist was used, resulting in a Ke of 81.4 nM (66.3-99.9, n = 6) against [D-Ala2, D-Leu5]-enkephalin, with a 3700-fold delta over mu or kappa selectivity ratio.

We have recently (Rónai et al., 1992) introduced a family of novel delta-opioid receptor-selective peptide antagonists, based on the Tyr-Pro-Gly-Phe-Leu-Thr structure, where the nitrogen accepts substituents that make protonation possible (e.g. diallyl) as well as substituents (e.g. t-Boc) where protonation cannot occur. In this paper, we present the details of a design strategy where the structurally closely related biologically active and inactive compounds are suggestive of conformational requirements of action. Furthermore, since even those derivatives of the antagonist peptides where the N-terminus was free were either devoid of opioid agonist activity or were extremely weak agonists, it is suggested that these antagonists do not interact with the conventional "opioid nitrogen site". To find this "conventional" site, a number of N-substituted (phenylglycyl-, alpha-Boc-lysyl-, alpha-Phe-beta-alanyl-) derivatives of Tyr-Pro-Gly-Phe-Leu-Thr hexapeptide were synthesized and their biological activities were determined in the mouse vas deferens bioassay.

Conventional opioids including opioid peptides require an "opioid" nitrogen which exists in protonated state while interacting with the receptor. In the present paper we demonstrate that the Tyr-Pro-Gly-Phe-Leu-Thr hexapeptide sequence accepts N-terminal substituents such as N-t-Boc, N-phenylacetyl and N-diphenylacetyl where the N cannot become protonated, as well as "traditional" substitutions such as N,N-diallyl, where protonation is likely under physiological conditions. The opioid peptides bearing these substituents are pure antagonists of medium affinity (Ke values in the mouse vas deferens bioassay against [Met5]-enkephalin are in the 3 x 10(-7)-4 x 10(-6) M range) with a high delta receptor preference (50-350-fold delta over mu selectivity ratios).

In isolated, perfused rabbit ear artery bradykinin, like [Met5]enkephalin and angiotensin II, inhibited neurogenic constrictions in concentrations lower than 10(-8) M without affecting the responses to exogenous norepinephrine. The IC50 value of bradykinin was 1.95 x 10(-10) M. The inhibitory action of bradykinin and angiotensin II but not of [Met5]enkephalin was reduced or even reversed by indomethacin pretreatment, suggesting that endogenous prostanoids are involved.

Angiotensin I and II inhibited the nerve stimulation-induced pressure changes in isolated, perfused rabbit ear artery with an IC50 of 3.07 and 0.36 nM, respectively. Neither angiotensin I nor angiotensin II affected the basal pressure or the pressure changes elicited by exogenously administered norepinephrine (NE). The potency of angiotensin I was unaltered by 10(-5) M captopril, indicating that conversion by angiotensin converting enzyme (ACE) was not necessary and did not take place. [Sar1,Val5,Ala8]angiotensin II (3 x 10(-8) M) antagonized the effect of angiotensin I. These findings could have implications regarding ACE inhibitor therapy and the pathophysiology of migraine.

The opioid activities of peptide and non-peptide narcotics were studied in longitudinal muscle strip of guinea pig ileum (GPI) and in mouse vas deferens (MVD). The comparison of agonist activities of peptides found in GPI and MVD offered the opportunity to predict the presence but not the magnitude of potential analgesic activity. The kinetics of the antagonism between naltrexone and different types of agonists were also determined in these systems. Using C-6 epimers of naltrexone, it was found that the site of opiate receptors recognizing the information provided by the C-6 substituent of naltrexone are different in GPI and MVD.

The binding of novel dibenzodioxazocine derivatives to rat striatal dopamine receptors was studied in vitro, using 3H-spiperone as radioligand. The biochemical-pharmacological characteristics of the effect of a selected representative, EGYT-2509 are discussed in details. The parameters of specific spiperone binding to rat striatal membrane preparation (KD = 0.550 nM, Bmax = 465 fmole/mg protein) as well as the displacing potencies of known dopamine receptor ligands matched closely the corresponding values in the literature. Using 0.4 nM radioligand, a Ki value of 404 nM was obtained for EGYT-2509; the binding of the drug had a minor serotonergic component. EGYT-2509 behaved as a dopamine receptor antagonist in all functional in vitro biochemical-pharmacological tests (striatal adenylate cyclase, striatal dopamine release, prolactin release from pituitary) performed previously. The drug exhibited a marked preference for adenylate cyclase-coupled (D1) dopamine receptors, followed by the 3H-spiperone displacing potency at striatal receptors. It was a rather weak antagonist both at striatal dopamine autoreceptors and at the receptors controlling prolactin release. Finally, when comparing the structure-activity relationships obtained with dibenzo-dioxazocines in the dopamine receptor binding assay with the relative pharmacological potencies of a structurally related neuroleptic group, i.e. of phenothiazines, a definite parallelism could be demonstrated.

The effects of morphine and a potent enkephalin analogue on spontaneous locomotion have been compared in mice. In doses of 3-10 mg/kg SC both compounds induced a brief reduction of motor activity followed by a period of behavioral hyperactivity. Similar receptorial mechanisms are suggested in mediation of their motor effects.

Evidence has been obtained that prazosin possesses a presynaptic alpha 2-adrenoceptor blocking action in the rat was deferens preparation stimulated at 1 Hz. In the presence of prazosin yohimbine failed to affect the presynaptic alpha 2-adrenoceptor stimulatory effect of 1-noradrenaline while the effect of xylazine was almost completely abolished. It is therefore suggested that there are two kinetically different prejunctional alpha 2-adrenoceptor sites.