Biomedical subjects

G Le Fur

Publications and source records attributed to G Le Fur.

At least 55 records · Page 3Linked to original sources

PubMed1998

The non-peptide neuroprotective agents SR 57746A interacts with neurotrophin 3 to induce differentiation in the PC12 cell-line.

SR 57746A (1-(2beta-naphthylethyl)-4-(3-trifluoromethylphenyl)-1,2,5,6 -tetrahydropyridine hydrochloride) is a neuroprotective compound which potentiates nerve-growth factor (NGF)-induced differentiation in PC12 cells. We have evaluated the interaction of SR 57746A with the other members of the neurotrophin family in this cell-line. In contrast with NGF, neurotrophin-3 did not increase the differentiation of PC12 cells. However, the association of SR 57746A with neurotrophin-3 significantly increased neurite outgrowth. No significant activity on neurite outgrowth was observed with brain-derived neurotrophic factor or neurotrophin-4, either alone or combined with SR 57746A. These results indicate that as well as potentiating the effect of NGF SR 57746A enables neurotrophin-3, which alone is inactive, to increase the differentiation of these cells.

Animals↗

PubMed1998

Both the immunosuppressant SR31747 and the antiestrogen tamoxifen bind to an emopamil-insensitive site of mammalian Delta8-Delta7 sterol isomerase.

SR31747 is a novel agent that elicits immunosuppressive and anti-inflammatory effects. This drug was shown to inhibit Delta8-Delta7 sterol isomerase in yeast. To test whether this enzyme could also be an SR31747 target in mammals, the binding, antiproliferative and sterol biosynthesis inhibitory properties of various drugs were studied in recombinant sterol isomerase-producing yeast cells. Our results clearly show that SR31747 is a high affinity ligand of recombinant mammalian sterol isomerase (Kd = 1 nM). Tridemorph, a sterol biosynthesis inhibitor that is widely used in agriculture as an antifungal agent, is also a powerful inhibitor of murine and human sterol isomerases (IC50 value in the nanomolar range). Some drugs, like cis-flupentixol, trifluoperazine, 7-ketocholestanol and tamoxifen, inhibit SR31747 binding only with the mammalian enzymes, whereas other drugs, like haloperidol and fenpropimorph, are much more effective with the yeast enzyme than with the mammalian ones. Emopamil, a high affinity ligand of human sterol isomerase, is inefficient in inhibiting SR31747 binding to its mammalian target, suggesting that the SR31747 and emopamil binding sites on mammalian sterol isomerase do not overlap. In contrast, SR31747 binding inhibition by tamoxifen is very efficient and competitive (IC50 value in the nanomolar range), indicating that mammalian sterol isomerase contains a so-called antiestrogen binding site. Tamoxifen is found to selectively inhibit sterol biosynthesis at the sterol isomerase step in the cells that are producing the mammalian enzyme in place of their own sterol isomerase. Finally, we also show that tridemorph, a sterol biosynthesis inhibitor widely used in agriculture as an antifungal agent, is not selective of yeast Delta8-Delta7 sterol isomerase but is also highly efficient against murine Delta8-Delta7 sterol isomerase or human Delta8-Delta7 sterol isomerase. This observation contrasts with our already published results showing that fenpropimorph, another sterol isomerase inhibitor used in agriculture, is only poorly efficient against the mammalian enzymes.

Animals↗

PubMed1998

Modulation of CB1 cannabinoid receptor functions after a long-term exposure to agonist or inverse agonist in the Chinese hamster ovary cell expression system.

We have investigated the adaptive changes of the human central cannabinoid receptor (CB1) stably expressed in Chinese hamster ovary cells (CHO-CB1), after agonist (CP 55,940) or selective CB1 inverse agonist (SR 141716) treatment. CB1 receptor density and affinity constant as measured by binding assays with both tritiated ligands remained essentially unchanged after varying period exposure of CHO-CB1 cells (from 30 min to 72 hr) to saturating concentrations of CP 55,940 or SR 141716. However, using a C-myc-tagged version of the CB1 receptor, FACS analysis and confocal microscopy studies on CB1 expression indicated that the agonist promoted a disappearance of cell surface receptor although inverse agonist increased its cell surface density. Taken together these results suggest that 1) agonist induces internalization of the receptor into a cellular compartment that would be still accessible to both the hydrophobic ligands CP 55,940 or SR 141716; 2) inverse-agonist promotes externalization of the receptor from an intracellular preexisting pool to the cell surface. In parallel, we also investigated the associated effects of CP 55,940 and SR 141716 on CB1 receptor-coupled second messengers. We showed that preexposure of cells to CP 55,940 induced a rapid desensitization of the CB1 to the agonist response. The ability of CP 55,940 to inhibit the forskolin-stimulated adenylyl cyclase and to activate the mitogen-activated protein kinase activity was dramatically reduced. By striking contrast, SR 141716 pretreatment of CHO-CB1 cells not only had no significant effect on the potency of CP 55,940 to inhibit the forskolin-stimulated adenylyl cyclase but also induced a significant enhancement of the CP 55,940 ability to stimulate the mitogen-activated protein kinase activity. These results suggest that the modulation of the number of cell surface receptor could lead to functional desensitization or sensitization of the CB1 receptors.

Animals↗

PubMed1997

Purification and characterization of the human SR 31747A-binding protein. A nuclear membrane protein related to yeast sterol isomerase.

SR 31747A, defined as a sigma ligand, is a novel immunosuppressive agent that blocks proliferation of human and mouse lymphocytes. Using a radiolabeled chemical probe, we here purified a target of SR 31747A and called it SR 31747A-binding protein (SR-BP). Purified SR-BP retained its binding properties and migrated on SDS-polyacrylamide gel as a Mr 28,000 protein. Cloning of the cDNA encoding human SR-BP shows an open reading frame for a 223-amino acid protein, which is homologous to the recently cloned sigma 1 receptor. Interestingly, the deduced amino acid sequence was found to be related to fungal C8-C7 sterol isomerase, encoded by the ERG2 gene. The ERG2 gene product has been identified recently as the molecular target of SR 31747A that mediates antiproliferative effects of the drug in yeast. Northern blot analysis of SR-BP gene expression revealed a single transcript of 2 kilobases which was widely expressed among organs, with the highest abundance in liver and the lowest abundance in brain. Subcellular localization analysis in various cells, using a specific monoclonal antibody raised against SR-BP, demonstrated that this protein was associated with the nuclear envelope. When studying the binding of SR 31747A on membranes from yeast expressing SR-BP, we found a pharmacological profile of sigma 1 receptors; binding was displaced by (+)-pentazocine, haloperidol, and (+)-SKF 10,047, with (+)-SKF 10, 047 being a more potent competitor than (-)-SKF 10,047. Scatchard plot analysis revealed Kd values of 7.1 nM and 0.15 nM for (+)-pentazocine and SR 31747A, respectively, indicating an affinity of SR-BP 50-fold higher for SR 31747A than for pentazocine. Additionally, we showed that pentazocine, a competitive inhibitor of SR 31747A binding, also prevents the immunosuppressive effect of SR 31747A. Taken together, these findings strongly suggest that SR-BP represents the molecular target for SR 31747A in mammalian tissues, which could be critical for T cell proliferation.

Amino Acid Sequence↗

PubMed1997

A selective inverse agonist for central cannabinoid receptor inhibits mitogen-activated protein kinase activation stimulated by insulin or insulin-like growth factor 1. Evidence for a new model of receptor/ligand interactions.

In the present study, we showed that Chinese hamster ovary (CHO) cells transfected with human central cannabinoid receptor (CB1) exhibit high constitutive activity at both levels of mitogen-activated protein kinase (MAPK) and adenylyl cyclase. These activities could be blocked by the CB1-selective ligand, SR 141716A, that functions as an inverse agonist. Moreover, binding studies showed that guanine nucleotides decreased the binding of the agonist CP-55,940, an effect usually observed with agonists, whereas it enhanced the binding of SR 141716A, a property of inverse agonists. Unexpectedly, we found that CB1-mediated effects of SR 141716A included inhibition of MAPK activation by pertussis toxin-sensitive receptor-tyrosine kinase such as insulin or insulin-like growth factor 1 receptors but not by pertussis toxin-insensitive receptor-tyrosine kinase such as the fibroblast growth factor receptor. We also observed similar results when cells were stimulated with Mas-7, a mastoparan analog, that directly activates the Gi protein. Furthermore, SR 141716A inhibited guanosine 5'-0-(thiotriphosphate) uptake induced by CP-55,940 or Mas-7 in CHO-CB1 cell membranes. This indicates that, in addition to the inhibition of autoactivated CB1, SR 141716A can deliver a biological signal that blocks the Gi protein and consequently abrogates most of the Gi-mediated responses. By contrast, SR 141716A had no effect on MAPK activation by insulin or IGF1 in CHO cells lacking CB1 receptors, ruling out the possibility of a direct interaction of SR 141716A with the Gi protein. This supports the notion that the Gi protein may act as a negative intracellular signaling cross-talk molecule. From these original results, which considerably enlarge the biological properties of the inverse agonist, we propose a novel model for receptor/ligand interactions.

Adenylate Cyclase Toxin↗

PubMed1997

Characterization and localization of leptin receptors in the rat kidney.

Characterization and localization of leptin binding sites were investigated in rat kidneys using [125I]leptin as a ligand. [125I]Leptin specific binding was found in high amounts in rat renomedullary membranes. This binding was specific, saturable, time-dependent (K(obs) = 0.055 +/- 0.008 min(-1)) and the dissociation of receptor-bound ligand was slowly reversible (K(-1) = 0.048 +/- 0.013 min(-1)). From saturation experiments, a single class of high-affinity binding sites for leptin was identified with an apparent K(d) of 0.57 +/- 0.14 nM and a B(max) of 45 +/- 10 fmol/mg protein. [125I]Leptin binding was inhibited in a dose-dependent manner by cold leptin and was highly selective since not displaceable by a number of other hormones or peptides. Autoradiographic experiments performed on adult rat kidney sections showed the intense presence of [125I]leptin receptors only in specific areas of the renal inner medulla and also consistent labeling associated with vascular structures in the corticomedullary region. The study of the postnatal developmental expression of leptin receptors in the kidney showed very low expression during the early postnatal period (8-21 days). Full expression of leptin sites was achieved at about 30 days and remained stable throughout adulthood (60 days and upwards). Moreover, in vivo administration of leptin (0.5 mg/kg i.p.) induced a significant and rapid diuretic effect in normally hydrated conscious rats. Thus, these data constitute the first characterization and mapping of [125I]leptin specific binding sites in the rat kidney and raise the possibility of a renal control by leptin.

Aging↗

PubMed1997

Involvement of cortical neurotensin in the regulation of rat meso-cortico-limbic dopamine neurons: evidence from changes in the number of spontaneously active A10 cells after neurotensin receptor blockade.

In order to further assess the role of endogenous neurotensin on midbrain dopaminergic neuronal function, the effects of the selective neurotensin receptor antagonists SR 48692 and SR 48527 were investigated on the number of spontaneously active A9 and A10 dopaminergic neurons in rats. Single intraperitoneal administration of SR 48692 (0.1-3 mg/kg) dose-dependently increased the number of active A10, but not A9 cells. SR 48527 (1 mg/kg) had a similar profile, but not SR 49711, its low affinity R-enantiomer, indicating that the effects observed were mediated through neurotensin receptor blockade. Five-week treatment with SR 48692 (3 mg/kg/day) produced a significant decrease of the number of active A10, but not A9 cells, which was reversed by apomorphine, suggesting that these cells were under depolarization block. Single co-administration of inactive doses of SR 48692 (0.1 mg/kg) and haloperidol (0.0625 mg/kg) significantly increased the number of active A10 cells. Conversely, co-administered active doses of SR 48692 or SR 48527 and haloperidol (1 and 0.25 mg/kg, respectively) induced an apomorphine-sensitive decrease of the number of A10 active cells. Finally, SR 48692 (10 mg/kg) modified neither accumbal nor cortical basal DA release. Local micro-injection of SR 48692 (10[-11]-10[-9] M), but not that of SR 49711 (10[-9] M), into the prefrontal cortex, increased the number of active A10 cells in a concentration-dependent manner. These results suggest that neurotensin receptor blockade counteracts a tonic inhibitory regulation by endogenous neurotensin of mesolimbic dopaminergic function and indicate that the prefrontal cortex is critically involved in this regulation.

Animals↗

PubMed1997

Selective inhibition of sucrose and ethanol intake by SR 141716, an antagonist of central cannabinoid (CB1) receptors.

SR 141716, a selective central CB1 cannabinoid receptor antagonist, markedly and selectively reduces sucrose feeding and drinking as well as neuropeptide Y-induced sucrose drinking in rats. SR 141716 also decreases ethanol consumption in C57BL/6 mice. In contrast, blockade of CB1 receptors only marginally affects regular chow intake or water drinking. The active doses of SR 141716 (0.3-3 mg/kg) are in the range known to antagonize the characteristic effects induced by cannabinoid receptor agonists. These results suggest for the first time that endogenous cannabinoid systems may modulate the appetitive value of sucrose and ethanol, perhaps by affecting the activity of brain reward systems.

Animals↗

PubMed1997

Involvement of potentially distinct neurotensin receptors in neurotensin-induced stimulation of striatal [3H]dopamine release evoked by KCl versus electrical depolarization.

We intended to determine whether the effect of neurotensin (NT) on K+ and electrically evoked [3H]dopamine (DA) release from rat and guinea-pig striatal slices involved different mechanisms and/or receptors. In the two species, NT and three NT agonists were found to exhibit different relative potencies to enhance K+- and electrically-evoked [3H]DA release. NT(1-13) increased [3H]DA release with EC50 values in the nanomolar range and Emax values in the range of 100% of control. NT(8-13) and Eisai hexapeptide were both as active as NT(1-13) under K+ depolarization, but did not exceed 40% of the NT(1-13) effect under electrical depolarization. In rats, when [3H]DA release was stimulated with two successive K+ depolarizations, in the presence of NT(1-13), the NT effect during the second exposure to K+ was drastically decreased, suggesting that the NT receptor was desensitized. The desensitization process was essentially observed on Emax values, EC50 values being weakly affected. Similar results were obtained in guinea pig. In contrast, with two electrical depolarizations or with two different depolarizations (K+ followed by electrical), the NT effect during the second depolarization was not significantly affected. Concerning NT antagonists, SR 48692 antagonized with IC50 values in the nanomolar range the NT(1-13) stimulated K+-evoked [3H]DA release but did not affect, up to 10(-6) M, the NT(1-13) enhancement of electrically stimulated [3H]DA release. On the contrary, SR 142948A antagonized the NT(1-13) effect on K+- and electrically-evoked [3H]DA release. In conclusion, these results suggest the possible existence of potentially distinct neurotensin receptors differentially involved in the control exerted by NT on DA release under KCl vs electrical depolarization.

Adamantane↗

PubMed1997

Biochemical and pharmacological activities of SR 144190, a new potent non-peptide tachykinin NK2 receptor antagonist.

(R)-3-(1-[2-(4-benzoyl-2-(3,4-difluorophenyl)-morpholin-2-yl)- ethyl]-4-phenylpiperidin-4-yl)-1-dimethylurea (SR 144190) is a new non-peptide antagonist of tachykinin NK2 receptors. SR 144190 potently and selectively inhibited neurokinin A binding to NK2 receptors from various species, including humans. In in vitro functional assays, it was a potent, selective and competitive antagonist of NK2 receptors with apparent affinities (pA2 values) between 9.08 and 10.10. In vivo, SR 144190 blocked [Nle10]neurokinin A-(4-10)-induced bronchoconstriction in guinea pigs (ID50 = 21 micrograms kg-1 i.v. and 250 micrograms kg-1 i.d.) and [beta Ala8]neurokinin A-(4-10)-induced urinary bladder contraction in rats (ID50 = 11 micrograms kg-1 i.v. and 190 micrograms kg-1 i.d.). It prevented citric acid-induced cough and airway hyperresponsiveness to acetylcholine in guinea pigs (1 mg kg-1 i.p.) as well as castor oil-induced diarrhoea in rats (0.01-10 micrograms kg-1 s.c. or p.o). Finally, it blocked the turning behaviour induced by intrastriatal injections of [Nle10]neurokinin A-(4-10) in mice (ID50 = 3 micrograms kg-1 i.v. and 16 micrograms kg-1 p.o.).

Animals↗

PubMed1997

Tachykinin neurokinin-1 and neurokinin-3 receptor-mediated responses in guinea-pig substantia nigra: an in vitro electrophysiological study.

The effects of tachykinin receptor agonists and antagonists were investigated using intra- and extracellular recordings on spontaneously firing nigral neurons in guinea-pig brain slices. In 70 of 76 electrophysiologically identified dopaminergic neurons, a concentration-dependent increase in firing rate was induced by the selective neurokinin-3 tachykinin agonist senktide and by the natural tachykinin agonists neurokinin B and substance P, with EC50 values of 14.7, 31.2 and 12200 nM respectively. These responses were inhibited in a concentration- and time-dependent manner by the selective non-peptide neurokinin-3 receptor antagonist SR 142801 (1-100 nM; n=23), but neither by its S-enantiomer SR 142806 (100 nM; n=4) nor by selective antagonists of neurokinin-1 (SR 140333) or neurokinin-2 (SR 48968) receptors (both at 100 nM; n=3). The selective neurokinin-1 agonist [Sar9,Met(O2)11]substance P (30-100 nM; n=23) and the selective neurokinin-2 agonist [Nle10]neurokinin A(4-10)(30-100 nM; n=13) were without any effect on dopaminergic cells. In 13 of 21 electrophysiologically identified, presumably GABAergic neurons located in the pars compacta of the substantia nigra, excitatory responses were evoked concentration dependently by substance P and [Sar9,Met(O2)11]substance P, with EC50 values of 18.6 and 41.9 nM respectively. These responses were inhibited by SR 140333 (100 nM; n=3), but neither by its R-enantiomer SR 140603 nor by SR 142801 (both at 100 nM; n=3). Senktide and [Nle10]neurokinin A(4-10) (both at 30-100 nM; n=10) were without effect on these presumed GABAergic neurons. A small population (12%) of pars compacta neurons was insensitive to any of the three selective tachykinin agonists. In the nigral pars reticulata, 12 neurons were recorded which had an electrophysiological profile similar to that of presumed GABAergic neurons in the pars compacta. Of these 12 cells, seven did not respond to any of the selective tachykinin agonists tested, while five were excited by senktide in a concentration-dependent manner (EC50=98.5 nM). Although this value was significantly higher than that found for dopaminergic neurons in the pars compacta, senktide-evoked responses were inhibited by SR 142801 (100 nM; n=3). We conclude that, in the guinea-pig substantia nigra, tachykinins evoke excitatory responses in both dopaminergic and non-dopaminergic neurons; however, the sensitivity to tachykinin agonists (neurokinin-1 versus neurokinin-3) depends on both neuronal type and localization.

Animals↗

PubMed1997

Negative modulation of nitric oxide production by neurotensin as a putative mechanism of the diuretic action of SR 48692 in rats.

1. We investigated the effect of the non-peptide neurotensin (NT) antagonist SR 48692 on renal function in rats and the involvement of nitric oxide (NO) in the diuretic action of this compound. 2. In fed animals, SR 48692 dose-dependently (0.5 to 12.5 mg kg-1, p.o., 0.03 to 1 mg kg-1, i.p. and 0.1 to 1 microgram/rat, i.c.v.) increased urine output and urinary excretion of Na+, K+ and Cl- and reduced urine osmolality. The diuretic activity was also evident in water-deprived, fasted animals and in fasted, water-loaded rats. 3. NT (0.1 microgram/rat, i.c.v.) had no effect on urine output in fed rats, but reduced the diuretic action of SR 48692 (1 microgram/rat, i.c.v.). The opposite result was obtained in fasted, water-loaded animals: NT dose-dependently (0.01 and 0.1 microgram/rat, i.c.v.) inhibited diuresis and this effect was significantly inhibited by i.c.v. SR 48692. In this experimental condition, SR 48692 did not further increase the on-going diuresis. 4. The NO synthesis inhibitor N(1)-nitro-L-arginine methyl ester (L-NAME; 30 mg kg-1, i.p.) alone had no effect on urine output in fed rats but prevented the diuretic action of i.c.v. or i.p. SR 48692; L-arginine (1 g kg-1, i.p.) but not D-arginine (1 g kg-1, i.p.) restored the SR 48692-dependent increase in diuresis, L-NAME had no effect on furosemide-stimulated diuresis. 5. Systemically administered L-NAME or i.c.v. NT in fasted, water-loaded rats significantly reduced water diuresis but this effect was no longer seen in animals given i.p. L-arginine. Rats receiving i.c.v. NT, whose diuresis was significantly reduced, also excreted less nitrates and nitrites in urine. 6. Increased diuresis after central or systemic administration of SR 48692 to fed rats was paralleled by increased urinary excretion of nitrates and nitrites, this being consistent with peripheral enhancement of NO production after NT-receptor blockade by SR 48692. The increase in diuresis after furosemide also involved an increase of nitrates and nitrites in urine, but this effect was about half that attained with an equipotent diuretic dose of SR 48692. 7. In fed rats, the NO donor isosorbide-dinitrate, reduced systolic blood pressure (unlike SR 48692 which did not affect blood pressure) but also dose-dependently (1 and 5 mg kg-1, i.p.) stimulated urine output. 8. The overall effects of SR 48692 strongly support a link between the actions of endogenous NT, AVP and peripheral NO production in the modulation of renal excretion of water, Na+, K+ and Cl-.

Animals↗

PubMed1997

Role of tachykinins in castor oil diarrhoea in rats.

1. We set out to ascertain the role of tachykinins, neurokinin A and substance P, in castor oil-induced diarrhoea in rats as disclosed by the inhibitory effect of the non-peptide NK1- and NK2-receptor antagonists. SR 140333 and SR 48968, respectively. 2. SR 48968 (0.02 to 20 micrograms kg-1, s.c. or p.o.), and the opioid receptor agonist loperamide (1-10 mg kg-1, p.o.), dose-dependently prevented castor oil effects: % inhibition vs castor oil, diarrhoea 0 to 100, increase in faecal mass 7 to 90 and water content 16 to 90. SR 140333 (0.02 to 20 micrograms kg-1, s.c.) and the platelet activating factor antagonist SR 27417 (5 to 500 micrograms kg-1, p.o.) did not prevent the increase in faecal water content, but reduced faecal mass (35 to 66%) and diarrhoea (0 to 57%). 3. The R-enantiomers of tachykinin NK1 and NK2 receptor antagonists, SR 140603 and SR 48605 (both at 2 or 20 micrograms kg-1, s.c.) had no effect other than reducing faecal mass at the highest dose tested. 4. SR 48968 (20 micrograms kg-1, p.o.) but not loperamide (10 mg kg-1, p.o.) given 24 h before castor oil, still slightly but significantly reduced by 30% the increase of faecal mass output; both treatments significantly reduced (30 to 70%) the effect of castor oil on faecal water content, although the incidence of diarrhoea was only slightly less than in controls. 5. In castor oil-treated rats, naloxone (2 mg kg-1, s.c.) completely blocked the antidiarrhoeal action of loperamide (10 mg kg-1, p.o.) but not of SR 48968 (20 micrograms kg-1, p.o.): a similar result was obtained on faecal mass and water content. 6. Castor oil strongly increased the occurrence of manometrically recorded propulsive giant contractions (500 to 1000% over control values) of transverse and distal colon, this effect being significantly prevented (80 to 100%) by SR 48968 and loperamide and partially by SR 140333 (35% distal colon, 70% transverse colon). 7. In castor oil free rats, loperamide but not SR 48968 or SR 140333 significantly reduced by 50% the gastrointestinal transit of a charcoal test meal, as well as 24 h faecal mass output. Consistently, loperamide, unlike the tachykinin receptor antagonists, had a dramatic effect on manometric recordings of intestinal motility, reducing all kinds of colonic contractions. 8. Our findings suggest that castor oil diarrhoea in rats entails activation of NK1 and NK2 receptors by endogenous tachykinins, whose antagonists may have a potential as antidiarrhoeal agents free from the constipating action of opioids.

Animals↗

PubMed1997

Characterization of CB1 receptors on rat neuronal cell cultures: binding and functional studies using the selective receptor antagonist SR 141716A.

This study was undertaken to characterize further the central cannabinoid receptors in rat primary neuronal cell cultures from selected brain structures. By using [3H]SR 141716A, the specific CB1 receptor antagonist, we demonstrate in cortical neurons the presence of a high density of specific binding sites (Bmax = 139 +/- 9 fmol/mg of protein) displaying a high affinity (KD = 0.76 +/- 0.09 nM). The two cannabinoid receptor agonists, CP 55940 and WIN 55212-2, inhibited in a concentration-dependent manner cyclic AMP production induced by either 1 microM forskolin or isoproterenol with EC50 values in the nanomolar range (4.6 and 65 nM with forskolin and 1.0 and 5.1 nM with isoproterenol for CP 55940 and WIN 55212-2, respectively). Moreover, in striatal neurons and cerebellar granule cells, CP 55940 was also able to reduce the cyclic AMP accumulation induced by 1 microM forskolin with a potency similar to that observed in cortical neurons (EC50 values of 3.5 and 1.9 nM in striatum and cerebellum, respectively). SR 141716A antagonized the CP 55940- and WIN 55212-2-induced inhibition of cyclic AMP accumulation, suggesting CB1 receptor-specific mediation of these effects on all primary cultures tested. Furthermore, CP 55940 was unable to induce mitogen-activated protein kinase activation in either cortical or striatal neurons. In conclusion, our results show nanomolar efficiencies for CP 55940 and WIN 55212-2 on adenylyl cyclase activity and no effect on any other signal transduction pathway investigated in primary neuronal cultures.

Animals↗

PubMed1997

Biochemical and pharmacological activities of SR 142948A, a new potent neurotensin receptor antagonist.

SR 142948A, 2-[[5-(2,6-dimethoxyphenyl)-1-(4-(N-(3-dimethylaminopropyl)-N-methylc arbamoyl)-2-isopropylphenyl)-1H-pyrazole3-carbonyl]amino] adamantane-2-carboxylic acid, hydrochloride, a new and extremely potent neurotensin (NT) receptor antagonist, has been characterized in comparison with SR 48692. This selective compound possesses nanomolar affinities for NT receptors, recognizes the two binding sites described for the NT receptor and fully displaces [3H]SR 48692 specific binding. SR 142948A antagonizes the classical in vitro NT effects, i.e., inositol monophosphate formation in HT 29 cells (IC50 = 3.9 nM) or intracellular calcium mobilization in Chinese hamster ovary cells transfected with the human receptor. It dose-dependently (0.04-640 x 10(-3) mg/kg p.o.) inhibits the turning behavior induced by unilateral intrastriatal injection of NT in mice, with the biphasic profile previously seen for SR 48692. At 0.1 mg/kg (i.p.), it completely antagonizes NT-evoked acetylcholine release in the rat striatum. In contrast to SR 48692, SR 142948A (p.o.) blocks both hypothermia and analgesia induced by i.c.v. injection of NT (mice and/or rats) but is unable to modify the dopamine release evoked by NT injection into the ventral tegmental area. In summary, SR 142948A retains the properties of the lead compound SR 48692 (no intrinsic agonist activity, oral bioavailability, long duration of action and good brain access), reveals a wider spectrum of activity than SR 48692 (probably due to the inhibition of NT receptor subtypes) and represents an additional tool for further exploration of the therapeutic potential of this class of compounds.

Adamantane↗

PubMed1997

Tachykinin-induced contractions of the guinea pig ileum longitudinal smooth muscle: tonic and phasic muscular activities.

In vitro tachykinin-induced contractions of guinea pig ileum longitudinal smooth muscle were investigated under isometric conditions by using selective agonists ([Sar9,Met(O2)11]substance P, [Nle10]neurokinin A-(4-10), senktide) and antagonists (SR 140333, SR 48968, SR 142801), respectively, for the tachykinin NK1, NK2, and NK3 receptors. [Sar9,Met(O2)11]Substance P (10 nM) induced a tonic contraction with superimposed phasic contractions. Both tonic and phasic muscular activities were completely abolished by SR 140333 (10 nM) and were not modified by SR 142801 (10 nM). SR 48968 (10 nM) and atropine (0.001 mM) did not modify the tonic muscular activity but inhibited the phasic muscular activity. [Nle10]Neurokinin A-(4-10) (10 nM) only caused a phasic contractile response that was inhibited by SR 48968. Atropine, SR 140333, and SR 142801 were without effect. Senktide (1 nM) induced combined tonic and phasic contractile responses. SR 142801 blocked the phasic and tonic muscular activities, whereas SR 48968 and SR 140333 were inactive. After addition of atropine, only tonic contractile response was abolished. These results showed fundamental differences in isometric tonic and phasic contractile responses of guinea pig ileum longitudinal smooth muscle to tachykinins.

Animals↗

PubMed1996

Effect of substance P on cytokine production by human astrocytic cells and blood mononuclear cells: characterization of novel tachykinin receptor antagonists.

Substance P (SP) has been reported to induce inflammatory cytokine production in human neuroglial cells and peripheral lymphoid cells as well. In order to evaluate the potency of novel non-peptide antagonists of the tachykinin receptors as inhibitors of SP-induced cytokines, we used the astrocytoma cell line U373MG and blood mononuclear cells as models of central and peripheral SP-target cells, respectively. In the first part of this study, we showed that SR 140333, an NK1 tachykinin receptor antagonist, was able to inhibit strongly the SP-induced production of interleukin (IL)-6 and IL-8 in the astrocytoma cell line. The antagonistic activity of SR 140333 toward SP-induced cytokine production was specific and could not be attributed to a general anti-cytokine effect, since cytokine release induced by another inflammatory protein such as IL-1beta was not blocked by this compound. In addition, NK2 and NK3 agonist neuropeptides were at least 1000-fold less effective than SP, while SR 48968 and SR 142801 which are selective NK2 and NK3 receptor antagonists, respectively, displayed a 2.5-3 orders of magnitude lower inhibitory potency than SR 140333. All these data indicated that SR 140333 blocked SP-induced cytokine production in U373MG astrocytic cells via a specific NK1 receptor-mediated process. Since SP has also been described to trigger peripheral blood mononuclear cells (PBMNC) or monocytes to release inflammatory cytokines, we attempted, in the second part of this study, to evaluate the potential antagonistic effect of our compounds on these cells. Experiments on human PBMNC from different donors were carried out to determine first their pattern of cytokine production upon SP stimulation. Surprisingly, we noticed that SP at concentrations ranging from 0.1 to 1000 nM was unable to stimulate the release of any inflammatory cytokine tested. This raises the question of the specificity of the reported in vitro effects of SP on cytokine production by human peripheral immune cells.

Astrocytes↗

PubMed1996

Characterization of SR 121463A, a highly potent and selective, orally active vasopressin V2 receptor antagonist.

SR 121463A, a potent and selective, orally active, nonpeptide vasopressin V2 receptor antagonist, has been characterized in several in vitro and in vivo models. This compound displayed highly competitive and selective affinity for V2 receptors in rat, bovine and human kidney (0.6 < or = Ki [nM] < or = 4.1). In this latter preparation, SR 121463A potently antagonized arginine vasopressin (AVP)-stimulated adenylyl cyclase activity (Ki = 0.26+/-0.04 nM) without any intrinsic agonistic effect. In autoradiographic experiments performed in rat kidney sections, SR 121463A displaced [3H]AVP labeling especially in the medullo-papillary region and confirmed that it is a suitable tool for mapping V2 receptors. In comparison, the nonpeptide V2 antagonist, OPC-31260, showed much lower affinity for animal and human renal V2 receptors and lower efficacy to inhibit vasopressin-stimulated adenylyl cyclase (Ki in the 10 nanomolar range). Moreover, OPC-31260 exhibited a poor V2 selectivity profile and can be considered as a V2/V1a ligand. In normally hydrated conscious rats, SR 121463A induced powerful aquaresis after intravenous (0.003-0.3 mg/kg) or oral (0.03-10 mg/kg) administration. The effect was dose-dependent and lasted about 6 hours at the dose of 3 mg/kg p.o. OPC-31260 had a similar aquaretic profile but with markedly lower oral efficacy. The action of SR 121463A was purely aquaretic with no changes in urine Na+ and K+ excretions unlike that of known diuretic agents such as furosemide or hydrochlorothiazide. In addition, no antidiuretic properties have been detected with SR 121463A in vasopressin-deficient Brattleboro rats. Thus, SR 121463A is the most potent and selective, orally active V2 antagonist yet described and could be a powerful tool for exploring V2 receptors and the therapeutical usefulness of V2 blocker aquaretic agents in water-retaining diseases.

Adenylyl Cyclases↗