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J Costentin

Publications and source records attributed to J Costentin.

At least 181 records · Page 10Linked to original sources
PubMed1987

Role of endogenous enkephalins in locomotion evidenced by acetorphan, an "enkephalinase" inhibitor.

To investigate whether endogenous enkephalins modulate locomotion we studied the effect of the systemic administration of acetorphan, a parenterally active "enkephalinase" inhibitor. Locomotor activity in mice and rats was considered as an index to the activity of mesolimbic dopaminergic neurons. Acetorphan injected i.v. induced an increase in locomotion, mice and rats presenting a similar behavioral response. Naloxone, at low doses, blocked the enhanced motor response. The increased locomotion was antagonized by a pretreatment with haloperidol or potentiated by GBR 12783, a potent and specific inhibitor of dopamine (DA) uptake. The neurotoxic lesion of the mesolimbic DA system with 6-hydroxydopamine abolished the effect of acetorphan. These data suggest that the locomotor hyperactivity induced by the enkephalinase inhibitor results from the protection of local endogenous enkephalins and may be mesolimbic DA-dependent.

Amino Acids, Sulfur↗
PubMed1987

Enantiomers of thiorphan and acetorphan: correlation between enkephalinase inhibition, protection of endogenous enkephalins and behavioral effects.

The relationships between various properties of inhibitors of enkephalinase (membrane metalloendopeptidase, EC 3.4.24.11) i.e., enzyme inhibition, protection of endogenous enkephalins, antinociceptive activity and stimulation of locomotor activity was investigated by comparing the relative potencies of the two enantiomers of Thiorphan and acetorphan, its parenterally active prodrug. In vitro (R)- and (S)-Thiorphan were almost equipotent in inhibiting enkephalinase activity (Ki, 1.7 and 2.2 nM, respectively) or thermolysin activity (Ki, 13 and 6 microM, respectively) whereas the (R)-isomer was 44-fold less potent than the (S)-isomer on ACE activity (Ki 4800 and 110 nM, respectively). When tested on slices of rat globus pallidus in the presence of bestatin, to block the aminopeptidase pathway of enkephalin degradation, both Thiorphan enantiomers ensured a complete protection of endogenous (Met5)enkephalin released by depolarization and a suppression of the increase in the extracellular levels of Tyr-Gly-Gly, a characteristic enkephalin metabolite. These two effects occurred at EC50 values of the two enantiomers (10 nM in both cases), consistent with the idea that they were due to enkephalinase inhibition. After i.v. administration of the acetorphan enantiomers to mice, the enkephalinase activity of a rapidly prepared striatal membrane fraction was reduced in a dose-dependent manner with similar "ex vivo" ED50 values (1.0 and 0.3 mg/kg for the (R)- and (S)-isomer, respectively). In contrast the ACE activity of the same preparation was reduced in a significant manner only by (S)-acetorphan (ED50 value of 11 mg/kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids, Sulfur↗
PubMed1986

Naloxone-insensitive potentiation of neurotensin hypothermic effect by the enkephalinase inhibitor thiorphan.

The hypothermic effect of neurotensin (0.1 microgram) injected i.c.v. in mice is potentiated by the enkephalinase inhibitor thiorphan (10 micrograms, i.c.v.). This potentiation is not reversed by systemic naloxone. The hypothermic effect of neurotensin is not modified by the amino-peptidase inhibitor bestatin (50 micrograms, i.c.v.) nor by the angiotensin-converting enzyme inhibitor captopril (50 micrograms, i.c.v.). These data indicate the involvement of enkephalinase in the inactivation of neurotensin, at least when it is injected i.c.v.

Amino Acids, Sulfur↗
PubMed1986

High-affinity [3H]GBR 12783 binding to a specific site associated with the neuronal dopamine uptake complex in the central nervous system.

We labelled the neuronal dopamine uptake system by using the potent dopamine uptake inhibitor GBR 12783 in its tritiated form (18.3 Ci/mmol). The binding of [3H]GBR 12783 to rat striatal membranes was saturable and specific with a Kd of 1.6 nM and a Bmax of 10.3 pmol X mg protein-1 as determined by Scatchard analysis. [3H]GBR 12783 binding to rat striatal membranes was inhibited by dopamine uptake inhibitors with IC50 highly correlated with their IC50 for inhibiting [3H]dopamine uptake by a rat striatal synaptosomal preparation. The rank order of potency was the following: GBR 12783 greater than amfonelic acid greater than mazindol greater than pyrovalerone greater than nomifensine greater than benztropine greater than amineptine greater than methylphenidate greater than cocaine. Substrates of dopamine uptake competed with [3H]GBR 12783 binding at concentrations higher than those at which they inhibited [3H]dopamine uptake. In rats with a unilateral section of the medial forebrain bundle, the decrease in [3H]GBR 12783 binding to membranes prepared from the ipsilateral striatum was equal to the decrease in [3H]dopamine uptake by a synaptosomal preparation obtained from the same striatum. [3H]GBR 12783 bound in a sodium-dependent manner to membranes prepared from striatum, nucleus accumbens and tuberculum olfactorium. GBR 12783 displayed an approximately 150-fold lower affinity for the cortical norepinephrine uptake system labelled with [3H]desipramine than for the dopamine transport complex labelled with [3H]GBR 12783. [3H]GBR 12783 appears an attractive tool for the selective characterization of the dopamine uptake system in vitro.

Animals↗
PubMed1986

Dissociated effects of inhibitors of enkephalin-metabolising peptidases or naloxone on various nociceptive responses.

The antinociceptive effects of Thiorphan, an 'enkephalinase' inhibitor, or bestatin, an aminopeptidase inhibitor, as well as of their association and the pronociceptive effects of naloxone, an opiate receptor antagonist, were evaluated in various analgesic tests in mice. These tests could be classified into two groups: (i) those tests in which the two peptidase inhibitors display naloxone-sensitive antinociceptive activity, particularly when administered together, and in which naloxone displays pronociceptive activity (vocalisation, hot-plate jump, writhing), (ii) those tests in which the two peptidase inhibitors and naloxone are ineffective (tail withdrawal, hot-plate licking, tail-flick). In contrast to the above, either morphine or [Met5]enkephalin in subthreshold dosage administrated together with the peptidase inhibitors displayed antinociceptive activity in the two groups of tests. The threshold dosages of morphine were the lowest in tests of the first group. The dissociated and opposite effects of peptidase inhibitors and naloxone per se might reflect a variable participation of endogenous enkephalins (or other opioid peptides) in the control of various nociceptive responses.

Analgesics↗
PubMed1986

GBR 12783, a potent and selective inhibitor of dopamine uptake: biochemical studies in vivo and ex vivo.

The effects of GBR 12783, an aryl 1,4-dialk(en)ylpiperazine derivative, were studied on the in vivo and ex vivo neuronal uptake of dopamine (DA), norepinephrine (NE) and serotonin (5HT). The drug inhibited potently (IC50 = 1.8 nM) and competitively the [3H]DA uptake by rat striatal synaptosomes. It produced significant [14C]DA release only at much higher concentrations (in the micromolar range). Depending on the animal species (rat or mouse) and the experimental conditions, GBR 12783 was 18-90 times and 85-300 times less effective against NE and 5HT uptake respectively than against DA uptake. In synaptosomes preloaded with [3H]DA, GBR 12783 added to the superfusion medium prevented the (+)amphetamine-induced DA release. The total binding of [3H]GBR 12783 to a membranal fraction prepared from striatum was lower than the binding to a synaptosomal fraction, suggesting its entry in synaptosomes. In addition, the concentration-dependent release of [3H]DA produced by GBR 12783 from a striatal vesicular fraction may account for the synaptosomal DA release promoted by micromolar concentrations of the drug. In ex vivo experiments, the ID50 for DA uptake inhibition (30 min after i.p. administration) was 8.1 mg/kg. After a dose of 10 mg/kg i.p., the striatal DA uptake inhibition occurred quickly (less than 10 min) and was long-lasting (greater than 5 h). The specificity of the drug for the DA uptake relative to NE and 5HT uptakes was also seen after i.p. administration of GBR 12783.

Animals↗
PubMed1986

Dissociated effects of apomorphine on various nociceptive responses in mice.

The effects of increasing doses of apomorphine were studied in mice in six nociceptive tests: (1) withdrawal of the tail immersed in hot water, (2) vocalization induced by the electrical stimulation of the tail, (3) tail flick using a radiant beam, (4) withdrawal of a tail-clip, (5) writhing induced by the i.p. injection of phenylbenzoquinone, (6) forepaw licking and jump latencies on a hot plate. Only in the tests (5) and (6), an apparent analgesia was obtained. Differences were observed between tests (5) and (6), as to: (i) the apparent relative effectiveness of (-)sulpiride (more effective in test [5] than in test [6]), (ii) the naloxone-induced modifications of apomorphine effects (whereas naloxone antagonized apomorphine effects in test [6], it did not in test [5]), (iii) the decrease of apomorphine-induced responses by prevention of hypothermia (in test [6] but not in test [5]). These data suggest that APO-induced increased jump latencies are at least partly related with hypothermia and endogenous opioid systems, whereas APO effect on the writhing test depends on the stimulation of dopamine receptors particularly sensitive to sulpiride and is independent from body temperature and opioidergic transmissions.

Analgesics↗
PubMed1986

Pharmacological properties of acetorphan, a parenterally active "enkephalinase" inhibitor.

Acetorphan, i.e. N-[(R,S)-3-acetylmercapto-2-benzylpropanoyl]-glycine, benzyl ester, is a lipophilic derivative of Thiorphan, a potent inhibitor of "enkephalinase" (EC 3.4.24.11). On purified enkephalinase its inhibitory potency was approximately 1000 fold less than that of Thiorphan but became close to the latter (nanomolar) when it was incubated previously with cerebral membranes. After parenteral administration to mice and rats (1-10 mg/kg) extensive inhibition of cerebral enkephalinase was shown by the depressed enzyme activity in brain membranes from treated animals and the long-lasting potentiation of analgesia elicited by (D-Ala2,Met5)enkephalin (i.c.v.). This suggests that acetorphan easily enters the brain where the active Thiorphan is released. Parenteral acetorphan elicited a series of naloxone-reversible, opioid-like effects, most of which were described previously with intracerebral Thiorphan or other enkephalinase inhibitors. Antinociceptive effects were found in some tests (hot plate jump and phenylbenzoquinone-induced writhing) but not in others (hot plate licking and tail withdrawal). "Antidepressant" effect was found in the "mouse despair" test and antidiarrhoeal effect in the rat castor oil test. Acetorphan also elicited significant increases and decreases in turnover indexes of serotonin and noradrenaline, respectively, in mouse cerebral cortex. In mice chronically treated with acetorphan, the antinociceptive activity of the compound was not modified markedly and no overt withdrawal symptom could be observed after either treatment interruption or administration of naloxone.

Amino Acids, Sulfur↗
PubMed1985

Unexpected potentiation by discriminant benzamide derivatives of stereotyped behaviours elicited by dopamine agonists in mice.

Among four stereotyped manifestations that can be simultaneously quantified in mice treated with apomorphine (APO), two of them (climbing and sniffing) emerge at low APO dosages (below 1 mg/kg) whereas licking and sniffing require APO dosages above 6 mg/kg. However, in mice pretreated (either i.p. or i.c.v.) with sulpiride (especially the levo isomer) or (+/-)amisulpride in moderate dosage stereotyped licking and sniffing are elicited by APO in much lower dosage (0.75 mg/kg). As a consequence, in mice pretreated with these benzamide derivatives and receiving 0.75 mg/kg APO, a biphasic effect was observed: licking and gnawing progressively appear at low dosages, whereas they are progressively abolished at higher dosages. This potentiation of the effects of APO by (+/-) amisulpride is even more obvious (maximal scores increased) with larger test-doses of the dopamine agonist (up to 5 mg/kg). Amisulpride also allows the emergence of the two stereotyped behaviours in mice receiving other dopamine agonists in subthreshold dosages (Dipropyl 5,6-ADTN, dexamphetamine or cocaine). The potentiation of APO is still observed after dopamine depletion by reserpine and alpha-methylparatyrosine, whereas that of dexamphetamine is abolished. In contrast with the benzamide derivatives, haloperidol does not potentiate at any dosage the effect of APO but, at 0.15 mg/kg, suppresses licking and gnawing elicited by 0.75 mg/kg APO in mice pretreated with 6.25 mg/kg amisulpride or veralipride.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

The discriminant dopamine antagonist property of benzamides is observed at various times after their systemic or intracerebroventricular administration.

The cataleptogenic effect or the antagonism of apormorphine-induced behaviour (climbing, sniffing, licking and yawning) shown by haloperidol, (+/-)sulpiride and (+/-)amisulpride were determined at different times after their intraperitoneal or intraventricular administration. After intraperitoneal injection, the ED50 or ID50 of haloperidol was similar for all the behavioural responses. On the other hand, sulpiride and amisulpride were effective on climbing and yawning in smaller doses than on sniffing, licking and catalepsy. The property of amisulpride to antagonize climbing at smaller doses than sniffing was still found whether this benzamide derivative was injected 30, 90, 150 or 240 min before testing. After the intraventricular administration of neuroleptics, a dissociated antagonist efficacy appeared for haloperidol, but that of sulpiride and amisulpride became much more marked than after their intraperitoneal injection. Amisulpride antagonized climbing in smaller doses than sniffing, whether administered intraventricularly 15, 30 or 120 min before testing. These results indicate that the dissociated dopamine antagonist efficacy of benzamides is long lasting and is observed even when the passage across the blood-brain barrier is avoided (i.c.v. route).

Animals↗
PubMed1985

Kelatorphan: a full inhibitor of enkephalin degrading enzymes. Biochemical and pharmacological properties, regional distribution of enkephalinase in rat brain by use of a tritiated derivative.

New potent inhibitors of enkephalin degrading enzymes were obtained by synthesis of compounds bearing a bidentate group. Among these bidentates, Kelatorphan, N-[(R)-3-(N-hydroxy)-carboxamido-2-benzylpropanoyl]-L-alanine, is in vitro a full inhibitor of enkephalinase, dipeptidylaminopeptidase and aminopeptidase. In vivo Kelatorphan (i.c.v. administered in mice) prevents exogenous enkephalin from peptidase degradation. The analgesic effect of Kelatorphan is at least equal to that of the association of bestatin and thiorphan. An analogue of Kelatorphan was tritiated and was used as a specific marker of enkephalinase. Thus the distribution of enkephalinase in rat brain was studied: striatum corpus and substantia nigra were particularly labelled.

Aminopeptidases↗
PubMed1985

New bidentates as full inhibitors of enkephalin-degrading enzymes: synthesis and analgesic properties.

New compounds were designed to fully inhibit the in vitro metabolism of enkephalins, ensured by three different metallopeptidases. For this purpose, bidentate ligands as hydroxamate and N-hydroxy-N-formylamino groups were selected as highly potent metal coordinating agents and introduced on Phe-Gly and Phe-Ala related structures. Compounds corresponding to the general formula HC(O)N(OH)CH2CH(CH2Ph)CONHCH2COOH (compound 7) and HN(OH)C(O)CH2CH(CH2Ph)CONHCH(R)COOH (compound 11, R = H; compound 13, R = CH3) behave as full inhibitors of the three enzymes, with IC50's in the nanomolar range for enkephalinase, from 0.3 microM to 1 nM for dipeptidylaminopeptidase, and in the micromolar range for a biologically relevant aminopeptidase. Two diastereoisomers of the most active inhibitor 13 were separated by HPLC and their stereochemistry was assigned by 1H NMR spectroscopy. Both isomers were efficient as enkephalinase blockers, but only the RS isomer, designated kelatorphan, was able to strongly inhibit aminopeptidase and dipeptidylaminopeptidase. Intracerebroventricular injection in mice of these mixed inhibitors, especially kelatorphan, led to naloxone reversible analgesic responses (hot-plate test) that were slightly better than those produced by a mixture of thiorphan and bestatin, two potent inhibitors of enkephalinase and aminopeptidase, respectively. Kelatorphan was also more efficient in potentiating the analgesia induced by a subanalgesic dose of Met-enkephalin. All these results support a physiological role in pain transmission for enkephalinase and a probably synaptic aminopeptidase M.

Aminopeptidases↗
PubMed1984

Analgesic effects of kelatorphan, a new highly potent inhibitor of multiple enkephalin degrading enzymes.

Kelatorphan, [(R)-3-(N-hydroxy)-carboxamido-2-benzylpropanoyl]-L-alanine, represents the first virtually complete inhibitor of enkephalins metabolism with KI = 1.4 nM against enkephalinase, KI = 2 nM against the Gly2 -Gly3 cleaving dipeptidylaminopeptidase and KI = 7 microM on aminopeptidase activity. The analgesic effect of [Met5]enkephalin was potentiated 50000 times (ED50 approximately 10 ng) by intracerebroventricular co-administration in mice of kelatorphan (50 micrograms). This effect was significantly higher than that produced by bestatin (50 micrograms) + thiorphan (50 micrograms). Kelatorphan alone was at least two-fold more potent as analgesic than the above mixture of inhibitors.

Aminopeptidases↗
PubMed1984

Simultaneous evaluation by a double labelling method of drug-induced uptake inhibition and release of dopamine in synaptosomal preparation of rat striatum.

Crude synaptosomal preparations from corpora striata of rat were preloaded with [14C]DA, rinsed, and then incubated with [3H]DA and the drug to be tested. During the 5 min of the second incubation, DA uptake and release rates were time- and temperature-dependent. On this double labelling test, nomifensine, cocaine, benztropine and amphetamines displayed IC50 and release curves similar to those obtained from separate uptake and release studies. In the presence of high concentrations of iprindole, amitriptyline and butriptyline (greater than 3 X 10(-6) M), a [14C]DA release was observed which closely coincided with an apparent inhibition of [3H]DA uptake. This double labelling test allows the determination of the participation of the releasing effect of drugs in their apparent inhibition of DA uptake.

Amphetamine↗
PubMed1984

Artefactual inhibition of dopamine uptake by psychotropic drugs on striatal synaptosomal preparation.

On striatal synaptosomal preparations, using a double labelling test, numerous antidepressant drugs demonstrated an inhibitory effect on [3H]DA uptake at the same high concentrations producing a [14C]DA release. This releasing effect was also shared by non-antidepressant agents and was observed on synaptosomes preloaded with [3H]5HT. The imipramine-induced release of DA was not modified by increasing concentration of K+, by decreasing concentration of Na+, by deleting Ca2+ from the incubation medium, or by blocking the catecholamine uptake systems with nomifensine or cocaine. The imipramine effect was reversible and was possibly initiated by a transient physico-chemical modification of the synaptosomal membrane. It was concluded that the DA uptake carrier is probably not involved in the effect of these drugs.

Animals↗
PubMed1984

The mu rather than the delta subtype of opioid receptors appears to be involved in enkephalin-induced analgesia.

The analgesic activity of some opioid peptides which display a relative selectivity for either the mu-receptor subtype, [D-Ala2, MePhe4, Gly-ol5]enkephalin (DAGO) or the delta-receptor subtype. [D-Ala2, D-Leu5]enkephalin (DADLE), [D-Ser2, Leu5]enkephalyl-Thr (DSLET) and [D-Thr2, Leu5]enkephalyl-Thr (DTLET) is highly correlated with their affinity for central or peripheral mu- but not delta-receptors. Moreover their analgesic effects as well as those elicited by degrading enzyme inhibitors (bestatin + thiorphan) of endogenous enkephalins were easily antagonized by naloxone with similar pA2 values but not by the delta-antagonist ICI 154,129. Therefore the analgesia produced by opioid peptides including endogenous enkephalins is likely connected to mu-receptor stimulation. Finally, there was no obvious potentiation by delta-agonists of the analgesia resulting from either administration of the mu-agonist morphine or endogenous enkephalins. This suggested that in the hot plate test, there is no modulation of the effect resulting from mu-receptor stimulation by a delta-receptor interaction. Likewise, enkephalinergic activity such as that due to thiorphan + bestatin does not appear to be regulated through mu- or delta-receptor stimulation.

Analgesics↗
PubMed1984

Involvement of endogenous enkephalins in the mouse 'behavioral despair' test.

In the mouse 'behavioral despair' test the immobility time was shortened by [D-Ala2,Met5]enkephalin at doses which did not modify locomotor activity. Similarly, the inhibitors of the enzymes degrading enkephalins, thiorphan and/or bestatin were effective. Their effect was antagonized by naloxone. We conclude that endogenous enkephalins are implicated in the 'behavioral despair' test.

Aminopeptidases↗