Effect of KW-3902, a selective adenosine A1-receptor antagonist, on accumulation of gentamicin in the proximal renal tubules in rats

Adenosine A1-receptor antagonists have been previously shown to possess protective effects in several nephrotoxic models of acute renal failure. To investigate the mechanism of protective effects of adenosine A1-receptor antagonists, we determined effects of 8-(noradamantan-3-yl)-1,3-dipropylxanthine (KW-3902), a selective adenosine A1-receptor antagonist, on the accumulation of gentamicin (GM) into proximal renal tubules in rats. GM was intravenously administered at a dose of 10 mg/kg in anesthetized rats. KW-3902 (0.1 mg/kg) or its vehicle was given as a bolus injection 6 min before the GM injection. Administration of GM and KW-3902 did not affect the systemic blood pressure, heart rate, renal blood flow and glomerular filtration rate. KW-3902 did not affect the plasma concentration of GM. GM was accumulated in the proximal tubules 4 h after the GM injection. Treatment with KW-3902 significantly decreased the accumulation of GM into the proximal tubules. These results suggest that endogenous adenosine may accelerate the uptake of GM at the proximal tubules, and that the renoprotective effects of the adenosine A1-receptor antagonist may result from inhibiting this action of endogenous adenosine, leading to the suppression of intrarenal accumulation of GM.     

The selective adenosine A1 receptor antagonist KW-3902 prevents radiocontrast media-induced nephropathy in rats with chronic nitric oxide deficiency

Several studies have recently suggested a principal role of adenosine in the pathogenesis of radiocontrast media-induced nephropathy. In the present experiments, we therefore investigated the renal protective effects of 8-(noradamantan-3-yl)-1,3-dipropylxanthine (KW-3902), a potent and selective adenosine A1 receptor antagonist, on radiocontrast media-induced nephropathy in the model of the N-pi-nitro-L-arginine methyl ester (L-NAME) hypertensive, chronic nitric oxide (NO)-depleted rat. Chronic NO depletion was induced by pretreatment with L-NAME, 50 mg/ml, added to drinking water for 8 weeks. Clearance experiments were performed in anesthetized rats and glomerular filtration rate was assessed prior to and following the application of high osmolar radiocontrast media (sodium diatrizoate, 3 ml/kg, i.v.) or an equivalent volume of isoosmolar mannitol to examine the role of hyperosmolarity in radiocontrast media-induced nephropathy. Subgroups received KW-3902 (0.1 mg/kg, i.v.), 20 min prior to radiocontrast media administration. Age-matched, untreated rats served as controls. Radiocontrast media application induced a significant decline in glomerular filtration rate in L-NAME hypertensive animals, whereas no effects were observed in control rats. KW-3902 fully prevented the drop in glomerular filtration rate in response to radiocontrast media in L-NAME hypertensive rats. No renal hemodynamic alterations were observed in mannitol-infused animals. The present experiments demonstrate that the decrease in glomerular filtration rate following radiocontrast media occurred independently of the osmotic load, and that KW-3902 effectively prevented the radiocontrast media-induced deterioration in renal function. KW-3902 may be especially beneficial in patients at high risk for developing acute renal failure following radiocontrast media application or in patients in which extracellular fluid volume expansion is limited by clinical conditions such as congestive heart failure.     

Effect of the selective adenosine A1-receptor antagonist KW-3902 on tubuloglomerular feedback in radiocontrast-media-induced nephropathy in rats with chronic nitric oxide deficiency

To study the possible mechanism of renoprotective effects of adenosine A1-receptor antagonist against radiocontrast media (RCM)-induced nephropathy, we investigated the effects of adenosine A1-receptor antagonist on tubuloglomerular feedback (TGF) activity prior to and following application of RCM in chronic NO-depleted rats. TGF in NO-depleted rats was significantly enhanced compared with that in normal rats. After RCM application, the enhanced TGF was continued. A selective adenosine A1-receptor antagonist, KW-3902 (8-(noradamantan-3-yl)-1,3-dipropylxanthine), inhibited the enhanced TGF. These results suggest that KW-3902 could inhibit TGF in chronic NO-depleted rats. Renoprotective effects by adenosine antagonists could be partly due to an inhibition of TGF via the blockade of the adenosine A1-receptor.     

Role of the lipid emulsion on an injectable formulation of lipophilic KW-3902, a newly synthesized adenosine A1-receptor antagonist

KW-3902 (a newly synthesized adenosine A1-receptor antagonist) has potent diuretic and renal protective activities. We investigated the influence of the emulsion formulation on the pharmacokinetics of KW-3902 and its metabolite (M1) in rats using three different formulations, i.e., a lipid emulsion about 130 nm in diameter composed of egg yolk lecithin: soybean oil: oleic acid=1:1:0.048, a liposome about 100 nm in diameter composed of egg yolk lecithin, and a saline solution containing 1% (v/v) each of dimethyl sulfoxide and 1 N NaOH. There was no significant difference in the pharmacokinetic parameters of KW-3902 (elimination half-life (T1/2), area under the plasma concentration-time curves (AUC0-infinity), total body clearance (CL), mean residence time (MRT) and volume of distribution at steady-state (Vdss) and M1 (Cmax, T1/2, AUC0-infinity and MRT) after injection of these three dosage forms. Moreover, we investigated in vitro the binding of KW-3902 to blood components using these three formulations. KW-3902 was completely partitioned into the blood components regardless of its dosage form. These findings suggested that KW-3902 dissociated rapidly from the lipid emulsion or liposome in blood after injection and showed intrinsic pharmacokinetics of KW-3902 at doses of 0.1 and 1 mg/kg. Thus, the lipid emulsion formulation of KW-3902 was defined as a solvent, which was a vehicle for dissolving the drugs to prepare the injection, at its expected effective doses.     

3H]OSIP339391, a selective, novel, and high affinity antagonist radioligand for adenosine A2B receptors

Until recently, the characterization of adenosine A(2B) receptors has been hampered by the lack of high affinity radioligands. This study describes the synthesis and in vitro characterization of the radiolabeled derivative of OSIP339391, a novel, potent, and selective pyrrolopyrimidine A(2B) antagonist. OSIP339391 had a selectivity of greater than 70-fold for A(2B) receptors over other human adenosine receptor subtypes. The radiolabel was introduced by hydrogenation of the acetylenic precursor with tritium gas resulting in the incorporation (on average) of three tritium atoms in the molecule, yielding a ligand with specific activity of 87Ci/mmol (3.2TBq/mmol). Using membranes from HEK-293 cells expressing the human recombinant A(2B) receptor, [3H]OSIP339391 was characterized in kinetic, saturation, and competition binding experiments. From the association and dissociation rate studies, the affinity was 0.41nM and in close agreement with that found in saturation binding experiments (0.17nM). In competition, binding studies using 0.5nM [3H]OSIP339391, the affinity of a range of agonists and antagonists was consistent with previously reported data. Thus, [3H]OSIP339391 is a novel, selective, and high affinity radioligand that can be a useful tool in the further exploration and characterization of recombinant and endogenous adenosine A(2B) receptors.     

Effect of the selective adenosine A1-receptor antagonist KW-3902 on lipopolysaccharide-induced reductions in urine volume and renal blood flow in anesthetized dogs

We investigated the effects of KW-3902 (8-noradamantan-3-yl-1,3-dipropylxanthine), a potent and selective adenosine A1-receptor antagonist, on lipopolysaccharide (LPS)-induced reduction of urine volume (UV) in anesthetized dogs, in comparison with those of furosemide. LPS was intravenously administered at a dose of 0.5 mg/kg; and the heart rate (HR), systemic blood pressure (BP), renal blood flow (RBF) and UV were measured every 15 min for 4 h. Administration of LPS continuously decreased HR, BP, RBF and UV. KW-3902, furosemide or their corresponding vehicle was given as a bolus injection 5 min after the LPS injection. Treatment with KW-3902 (1 mg/kg, i.v.) ameliorated the LPS-induced decline of UV and RBF. Furosemide (3.2 mg/kg, i.v.) tended to ameliorate the LPS-induced decline of UV but not RBF, the duration of the effect being shorter than that of KW-3902. These results suggest that KW-3902 can ameliorate the oliguria and the decrease in RBF during the early phase of LPS-induced shock. Endogenous adenosine may be involved in the endotoxin-induced oliguria via the adenosine A1-receptor.     

Pharmacological characterization of FR194921, a new potent, selective, and orally active antagonist for central adenosine A1 receptors

Adenosine A1 receptors in the brain are believed to play an important role in brain functioning. We have discovered a novel adenosine A1 receptor antagonist, FR194921 (2-(1-methyl-4-piperidinyl)-6-(2-phenylpyrazolo[1,5-a]pyridin-3-yl)-3(2H)-pyridazinone), and characterized the pharmacological activity in the present study. FR194921 showed potent and selective affinity for the adenosine A1 receptor without affinity for A2A and A3 receptors and did not show any species differences in binding affinity profile among human, rat, and mouse. Pharmacokinetic study in rats revealed that FR194921 was orally active and highly brain penetrable. Oral administration of FR194921 dose-dependently ameliorated the hypolocomotion induced by the A1 receptor agonist N6-cyclopentyladenosine in rats, indicating this compound exerts A1-antagonistic action in vivo. In the passive avoidance test, scopolamine (1 mg/kg)-induced memory deficits were significantly ameliorated by FR194921 (0.32, 1 mg/kg). In two animal models of anxiety, the social interaction test and elevated plus maze, FR194921 showed specific anxiolytic activity without significantly influencing general behavior. In contrast, FR194921 did not show antidepressant activity even at a dose of 32 mg/kg in the rat forced swimming test. These results indicate that the novel, potent, and selective adenosine A1 receptor antagonist FR194921 exerts both cognitive-enhancing and anxiolytic activity, suggesting the therapeutic potential of this compound for dementia and anxiety disorders.     

125I-BW-A844U, an antagonist radioligand with high affinity and selectivity for adenosine A1 receptors, and 125I-azido-BW-A844U, a photoaffinity label

3-(4-Amino)phenethyl-1-propyl-8-cyclopentylxanthine (BW-A844U) has been synthesized and shown to bind with high affinity to adenosine A1 receptors of bovine brain membranes (KD = 0.23 nM). This compound is highly selective for A1 receptors; the KI for binding to A2 receptors of human platelet membranes is 2.0 microM (A2/A1 ratio = 8700). Radioiodination of the 3-aminophenethyl group resulted in 125I-BW-A844U, a radioligand that retains high affinity for A1 receptors in bovine brain membranes (KD = 0.14 nM) and to 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate-solubilized receptors (KD = 0.34 nM). Specific binding of 125I-BW-A844U represented greater than 90% of the total binding at the KD. From the association constant (K1 = 5.0 X 10(8) M-1min-1) and the dissociation constant (K-1 = 0.064 min-1), the kinetic KD (K-1/K1) in membranes was calculated to be 0.13 nM. NaCl (1 M) had little effect on the binding affinity of 125I-BW-A844U, in contrast to the large effect of salt on the binding affinity of acidic antagonist radioligands. 8-Sulfophenyltheophylline inhibited radioligand binding with a Hill coefficient of 1.0, indicative of a single affinity binding state for the antagonist. By comparison, two distinct agonist affinity states of A1 receptors for the agonist (R)-phenylisopropyladenosine could be resolved, a high affinity state (62%, KH = 74 pM) and a low affinity state (KL = 3.83 nM). The addition of 0.1 mM guanylylimidodiphosphate converted all receptors to the low affinity state. Addition of NaCl (0.5 M) decreased the fraction of receptors in the high affinity state and increased both KH and KL, suggesting that NaCl alters coupling of receptors to G proteins and influences the conformation of the receptor polypeptide, whether or not the receptor is coupled to a G protein. Conversion of the arylamine on the 3-position of 125I-BW-A844U to an aryl azide resulted in a photoaffinity label, 125I-azido-BW-A844U. Upon photoactivation, the photoaffinity label was specifically photoincorporated into the 34,000-dalton polypeptide of the adenosine A1 receptor.     

A new high affinity, iodinated adenosine receptor antagonist as a radioligand/photoaffinity crosslinking probe

A new high affinity antagonist photoaffinity crosslinking radioligand has been synthesized for use in studying adenosine receptors. This compound, PAPAXAC (8-[-4-[[[[[2-(4-aminophenylacetylamino)ethyl]amino]carbonyl]- methyl]oxy]phenyl]-1,3-dipropylxanthine), has been labeled with 125I by a chloramine T method. The radioligand [125I]PAPAXAC binds to A1 adenosine receptors from bovine cerebral cortex with high affinity (KD = 0.1 nM), appropriate stereoselectivity, and A1 adenosine receptor specificity. Binding is not perturbed by guanine nucleotides. Adenylate cyclase assays document that PAPAXAC is an antagonist capable of completely blocking the ability of N6-R-phenyl-2-propyladenosine (R-PIA) to inhibit adenylate cyclase activity via A1 adenosine receptors. [125I]PAPAXAC can be incorporated covalently into a peptide of Mr = 40,000 using the heterobifunctional crosslinking agent N-succinimidyl-6-(4'-azido-2'-nitrophenylamino)hexanoate. Covalent labeling can be inhibited with adenosine receptor ligands to demonstrate a potency series of R-PIA greater than S-PIA greater than NECA much greater than IBMX. Guanine nucleotides do not decrease covalent incorporation. These results suggest that antagonists such as [125I]PAPAXAC recognize the same A1 adenosine receptor-binding subunit as agonists, such as [125I]AZPNEA, which labels a similar Mr peptide with the same pharmacological potency series. This new antagonist photoaffinity crosslinking probe/radioligand should be of great utility in the molecular characterization of A1 adenosine receptors.     

3H]MRS 1754, a selective antagonist radioligand for A(2B) adenosine receptors

MRS 1754 [N-(4-cyanophenyl)-2-[4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purin-8-yl)-phenoxy]acetamide] is a selective antagonist ligand of A(2B) adenosine receptors. This is the least well-defined adenosine receptor subtype, and A(2B) antagonists have potential as antiasthmatic drugs. For use as a radioligand, MRS 1754, a p-cyanoanilide xanthine derivative, was tritiated on the propyl groups in a two-step reaction using a p-carboxamido precursor, which was dehydrated to the cyano species using trifluoroacetic anhydride. [3H]MRS 1754 (150 Ci/mmol) bound to recombinant human A(2B) adenosine receptors in membranes of stably transfected HEK-293 cells. Specific binding was saturable, competitive, and followed a one-site model, with a K(D) value of 1.13 +/- 0.12 nM and a B(max) value of 10.9 +/- 0.6 pmol/mg protein. Specific binding utilizing 0.7 nM [3H]MRS 1754 was > 70% of total binding. The affinity calculated from association and dissociation binding constants was 1.22 nM (N = 4). Binding to membranes expressing rat and human A(1) and A(3) adenosine receptors was not significant, and binding in membranes of HEK-293 cells expressing human A(2A) receptors was of low affinity (K(D) > 50 nM). The effects of cations and chelators were explored. Specific binding was constant over a pH range of 4.5 to 6.5, with reduced binding at higher pH. The pharmacological profile in competition experiments with [3H]MRS 1754 was consistent with the structure-activity relationship for agonists and antagonists at A(2B) receptors. The K(i) values of XAC (xanthine amine congener) and CPX (8-cyclopentyl-1,3-dipropylxanthine) were 16 and 55 nM, respectively. NECA (5'-N-ethylcarboxamidoadenosine) competed for [3H]MRS 1754 binding with a K(i) of 570 nM, similar to its potency in functional assays. Thus, [3H]MRS 1754 is suitable as a selective, high-affinity radioligand for A(2B) receptors.     

Functionalized congeners of adenosine: preparation of analogues with high affinity for A1-adenosine receptors

A series of functionalized congeners of adenosine based on N6-phenyladenosine, a potent A1-adenosine receptor against, was synthesized. Derivatives of the various congeners should be useful as receptor and histochemical probes and for the preparation of radioligands and affinity columns or as targeted drugs. N6-[4-(Carboxymethyl)phenyl]adenosine served as the starting point for synthesis of the methyl ester, the methyl amide, the ethyl glycinate, and various substituted anilides. One of the latter, N6-[4-[[[4-(carbomethoxymethyl)anilino]carbonyl]methyl]phenyl] adenosine, served as the starting point for the synthesis of another series of congeners including the methyl amide, the hydrazide, and the aminoethyl amide. The terminal amino function of the last congener was acylated to provide further analogues. The various congeners were potent competitive antagonists of binding of N6-[3H]cyclohexyladenosine to A1-adenosine receptors in rat cerebral cortical membranes. The affinity of the congener for the A1 receptor was highly dependent on the nature of the spacer group and the terminal moiety with Ki values ranging 1-100 nM. A biotinylated analogue had a Ki value of 11 nM. A conjugate derived from the Bolton-Hunter reagent had a Ki value of 4.5 nM. The most potent congener contained a terminal [(aminoethyl)amino]carbonyl function and had a Ki value of less than 1 nM.     

The diuretic action of 8-cyclopentyl-1,3-dipropylxanthine, a selective A1 adenosine receptor antagonist.

1. The diuretic effect of the selective A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (CPX), was investigated in anaesthetized rats. 2. CPX (0.1 mg kg-1, i.v.) produced significant increases in urine flow, and the excretion rate and fractional excretion of both sodium and chloride. By contrast, CPX administration did not result in any significant change in the excretion of potassium. 3. The diuretic effect of CPX was accompanied by a transient increase in inulin clearance although p-amino-hippurate clearance was unaffected, indicating the CPX induced a temporary elevation of glomerular filtration rate but no change in renal blood flow. 4. The fractional excretion of lithium (a marker of delivery of fluid out of the proximal tubule) was also significantly increased by CPX. However, other measures of tubular function derived from lithium clearance indicated that there were no changes in the handling of sodium or water in the distal regions of the nephron. 5. CPX did not significantly alter the relationship between either free water reabsorption or free water clearance and the distal delivery of sodium, which suggests that CPX does not affect the renal concentration/dilution mechanism. 6. The results of this study show that the diuresis and increased excretion of sodium and chloride induced by CPX (0.1 mg kg-1) in the rat, occurs with only transient elevation in glomerular filtration rate and no change in renal blood flow. The primary reason for the diuresis appears to be inhibition of sodium reabsorption in the proximal tubule.(ABSTRACT TRUNCATED AT 250 WORDS)     

The M2 selective antagonist AF-DX 116 shows high affinity for mnscarine receptors in bovine tracheal membranes

Summary We have characterized the muscarine receptors in bovine tracheal and left ventricular membranes using ³H-dexetimide/pirenzepine and ³H-dexetimide/AF-DX 116 competition studies. Pirenzepinc exhibited low (M₂) affinity binding to both preparations; K _d was 590 nM in left ventricle and 463 nM in trachea. AF-DX 116 exhibited high (M₂) affinity binding to left ventricle (K _d = 95.6 nM); in tracheal membranes it bound with high (M₂) affinity (K _d = 40.7 nM) to 74% of the receptors and with low (M₃) affinity (K _d = 2.26 M) to 26% of the receptors. It is concluded that bovine tracheal muscle membranes contain a heterogeneous population of muscarine binding sites, the majority having M₂ (heart) subtype characteristics and being located on the smooth muscle membranes; a minority having M₃ (exocrine gland) subtype characteristics and presumed to be located in submucosal glands. This is the first report of high affinity binding of AF-DX 116 to non-cardiac peripheral muscarine receptors. Send offprint requests to A. F. Roffel at the above address     

The antihypertensive effect of 2-alkynyladenosines and their selective affinity for adenosine A2 receptors

We examined the affinity for adenosine receptors and the antihypertensive effects of 2-alkynyladenosines, especially 2-hexynyladenosine (2-H-Ado) and 2-octynyladenosine (2-O-Ado). The order of decreasing affinity of 2-H-Ado, 2-O-Ado, and other agonists tested for A1 receptors was N6-cyclopentyladenosine (CPA) greater than N6-cyclohexyladenosine (CHA) greater than N6-R-phenylisopropyladenosine (R-PIA) greater than 2-chloroadenosine (CADO) = 5'-N-ethylcarboxamideadenosine (NECA) greater than N6-S-phenylisopropyladenosine (S-PIA) greater than 2-H-Ado greater than 2-O-Ado greater than 2-phenylaminoadenosine (CV-1808), and that for A2 receptors was 2-H-Ado greater than 2-O-Ado = NECA greater than CADO greater than CV-1808 greater than R-PIA greater than CPA greater than CHA greater than S-PIA. The Ki values of 2-H-Ado and 2-O-Ado for [3H] NECA binding to A2 receptors were 4.1 and 12.1 nM, respectively, and those for [3H]CHA binding to A1 receptors were 146 and 211 nM, respectively: the affinity of 2-H-Ado and 2-O-Ado for A2 receptors was about 36- and 17-fold higher than their affinity for A1 receptors. Injection of 2-H-Ado and 2-O-Ado (0.03-100 micrograms/kg) decreased the blood pressure of anaesthetized spontaneously hypertensive rats (SHR). A slight decrease in heart rate was observed after i.v. injection of 100 micrograms/kg 2-H-Ado and 2-O-Ado. A potent and long-lasting antihypertensive effect was also observed after oral administration of 2-H-Ado and 2-O-Ado to conscious SHR.(ABSTRACT TRUNCATED AT 250 WORDS)     

Agomelatine and tianeptine antidepressant activity in mice behavioral despair tests is enhanced by DMPX,a selective adenosine A2A receptor antagonist,but not DPCPX,a selective adenosine A1 receptor antagonist

BackgroundAdenosine, an endogenous nucleoside, modulates the release of monoamines, e.g., noradrenaline, serotonin, and dopamine in the brain. Both nonselective and selective stimulation of adenosine receptors produce symptoms of depression in some animal models. Therefore, the main objective of our study was to assess the influence of a selective adenosine A₁ receptor antagonist (DPCPX) and a selective adenosine A_2A receptor antagonist (DMPX) on the activity of agomelatine and tianeptine.MethodsThe forced swim test (FST) and tail suspension test (TST) were performed to assess the effects of DPCPX and DMPX on the antidepressant-like activity of agomelatine and tianeptine. Drug serum and brain levels were analyzed using HPLC.ResultsCo-administration of agomelatine (20 mg/kg) or tianeptine (15 mg/kg) with DMPX (3 mg/kg), but not with DPCPX (1 mg/kg), significantly reduced the immobility time both in the FST and TST in mice. These effects were not associated with an enhancement in animals’ spontaneous locomotor activity. The observed changes in the mouse behavior after concomitant injection of DMPX and the tested antidepressant agents were associated with elevated brain concentration of agomelatine and tianeptine.ConclusionOur study shows a synergistic action of the selective A_2A receptor antagonist and the studied antidepressant drugs, and a lack of such interaction in the case of the selective A₁ receptor antagonist. The interaction between DMPX and agomelatine/tianeptine at least partly occurs in the pharmacokinetic phase. A combination of a selective A_2A receptor antagonist and an antidepressant may be a new strategy for treating depression.     

Effects of a selective adenosine A1 receptor antagonist on the development of cyclosporin nephrotoxicity.

1. The clinical application of cyclosporin as an immunosuppressive agent is limited by its nephrotoxicity. 2. The effect of FK453, a selective A1-receptor antagonist, administered twice daily to rats at a dose of 100 mg kg-1 was assessed on the development of nephrotoxicity induced by cyclosporin (10 mg kg-1 i.p. daily) administered for 14 days. The effects of nifedipine administered twice daily (0.3 mg kg-1 s.c.) for 14 days, on cyclosporin nephrotoxicity were also studied. 3. Cyclosporin induced a 46.58% and 35.78% decline in glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) respectively and a reduction of 16.69% in filtration fraction (FF). Co-administration of FK453 resulted in falls of 30.5%, 18.59% and 14.7% in GFR, ERPF and FF respectively, the former two significantly less than the falls seen with cyclosporin (CyA) alone (P < 0.05 vs CyA, ANOVA). 4. Nifedipine appeared to have a more pronounced protective effect resulting in a decline of only 20.91% in GFR, with no significant change in ERPF (increase of 0.93%) when co-administered with CyA. 5. These observations indicate adenosine plays a minor role in the pathophysiology of CyA nephrotoxicity.     

GR113808: a novel, selective antagonist with high affinity at the 5-HT4 receptor.

1. The 5-HT4 receptor has only recently been identified but has yet to be cloned. This paper describes the pharmacology of a potent and selective 5-HT4 receptor antagonist, GR113808, which will be useful in the further characterization of this receptor. 2. On the guinea-pig ascending colon, GR113808 (1 nM-0.1 microM) behaved as an antagonist of 5-hydroxytryptamine (5-HT)-induced contraction, producing rightward displacements of the concentration-effect curve to 5-HT and a concentration-related depression of the maximum effect. However, the compound had no effect on cholecystokinin (CCK-8)-induced contraction in concentrations up to 1 microM. 3. In the guinea-pig colon preparation, onset and offset of the antagonism by GR113808 of 5-HT-induced contraction was examined. Incubation of the tissues for either 15 min, 30 min or 60 min produced similar rightward displacements of the concentration-effect curves to 5-HT, with no increase in the degree of depression of the maxima with increasing time of incubation. Experiments examining offset of antagonism (0.01 microM) demonstrated that washout for 30 min was required to reverse fully the effects of the antagonist. 4. Potency estimates in the colon for GR113808 were made by determining approximate pA2 values (30 min) using the Gaddum equation. The values obtained were 9.2, 9.7 and 9.2 when tested against the agonists 5-HT, 5-methoxytryptamine and R,S-zacopride respectively. 5. On the carbachol-contracted tunica muscularis mucosae preparation of the rat thoracic oesophagus, GR113808 behaved as an antagonist of 5-HT-induced relaxation, producing no reduction in maximum response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thyroid receptor ligands. 6. A high affinity "direct antagonist" selective for the thyroid hormone receptor

A new high-affinity thyroid hormone antagonist 6 with druglike properties was designed and synthesized. The compound behaved as an antagonist in a cell transactivation assay, and in a first in vivo experiment in rats.     

Blockade of human atrial 5-HT4 receptors by SB 207710, a selective and high affinity 5-HT4 receptor antagonist

The mode of antagonism of 5-hydroxytryptamine-induced positive inotropic effects by the highly selective 5-HT₄ receptor antagonist SB 207710 (1-butyl4-piperidinyl) methyl 8-amino-7-iodo-1,4-benzodioxan-5-carboxylate was investigated on isolated preparations of human right atrial appendage. SB 207 710 caused concentration-dependent (0.1–10 nmol/l) surmountable antagonism of the effects of 5-hydroxytryptamine with a pK_B (mol/l) of 10.1. Due to its high selectivity and affinity, SB 207710 could be a powerful tool for the comparison of human atrial 5-HT₄ receptors with 5-HT₄ receptors of other organs of man and other species.     

Pharmacological profile of a high affinity dipeptide NK1 receptor antagonist, FK888.

1. In our search for compounds that inhibit the binding of [3H]-substance P (SP) to guinea-pig lung membranes, the dipeptide SP antagonist, FK888, was developed by chemical modification of the parent compound, (D-Pro4, D-Trp7,9,10, Phe11)SP4-11. 2. In a [3H]-SP binding assay using guinea-pig lung membranes and rat brain cortical synaptic membranes, FK888 displaced [3H]-SP binding with a Ki value of 0.69 +/- 0.13 nM and 0.45 +/- 0.17 microM, respectively, in a competitive manner. 3. FK888 inhibited the contraction of guinea-pig isolated ileum induced by SP in the presence of atropine and indomethacin (a NK1 receptor bioassay) with a pA2 value of 9.29 (8.60-9.98). 4. FK888 inhibited contractions of rat vas deferens by NKA (a NK2 receptor bioassay) and of rat portal vein by NKB (a NK3 receptor bioassay) at concentrations at least 10,000 times greater than that required to inhibit contractions of guinea-pig ileum. 5. FK888 also inhibited SP-induced airway oedema in guinea-pig after both intravenous and oral administration. 6. These data demonstrate that FK888 is a potent and selective NK1 antagonist which is active both in vitro and in vivo.