Selective Tachykinin NK1 Receptor Agonists Research Articles

Pharmacology of MEN 11467: a potent new selective and orally- effective peptidomimetic tachykinin NK1 receptor antagonist

We have investigated the pharmacological properties of MEN 11467, a novel partially retro-inverse peptidomimetic antagonist of tachykinin NK1 receptors. MEN 11467 potently inhibits the binding of [3H] substance P (SP) to tachykinin NK1 receptors in the IM9 limphoblastoid cell line (pKi = 9.4 ± 0.1). MEN 11467 is highly specific for the human tachykinin NK1 receptors, since it has negligible effects (pKi <6) on the binding of specific ligands to tachykinin NK2 or NK3 receptors and to a panel of 30 receptors ion channels unrelated to tachykinin receptors. The antagonism exerted by MEN 11467 at tachykinin NK1 receptors is insurmountable in saturation binding experiments, both KD and Bmax of SP were significantly reduced by MEN 11467 (0.3–10nM). In the guinea-pig isolated ileum, MEN 11467 (0.03–1nM) produced a nonparallel rightward shift of the concentration–response curve to SP methylester with a concomitant reduction of the Emax to the agonist (pKB = 10.7 ± 0.1). Moreover the antagonist activity of MEN 11467 was hardly reversible despite prolonged washout. In vivo, MEN 11467 produced a long lasting (> 2–3h) dose-dependent antagonism of bronchoconstriction induced by the selective tachykinin NK1 receptor agonist, [Sar9, Met(O2)11]SP in anaesthetized guinea-pigs (ID50s' = 29±5, 31±12 and 670±270μg/kg, after intravenous, intranasal and intraduodenal administration, respectively), without affecting bronchoconstriction induced by methacholine. After oral administration MEN 11467 produced a dose-dependent inhibition of plasma protein extravasation induced in guinea-pig bronchi by [Sar9, Met(O2)11] (ID50 = 6.7 ± 2mg/kg) or by antigen challenge in sensitized animals (ID50 = 1.3mg/kg). After i.v. administration MEN 11467 weakly inhibited the GR 73632-induced foot tapping behaviour in gerbil (ED50 = 2.96 ± 2mg/kg), indicating a poor ability to block central tachykinin NK1 receptors. These results demonstrate that MEN 11467 is a potent, highly selective and orally effective insurmountable pseudopeptide antagonist of peripheral tachykinin NK1 receptors with a long duration of action.

Inflammatory and motor responses by tachykinins in the guinea-pig oesophageal sphincter.

1. The aim of this study was to characterize the tachykinin receptors involved in producing plasma protein extravasation and contractile responses of the guinea-pig oesophageal sphincter. 2. In anaesthetized guinea-pigs, the selective tachykinin NK-1 receptor agonist [Sar9,Met(O2)11]substance P produced plasma protein extravasation (PPE) which was not affected by the treatment with the tachykinin NK-2 receptor antagonist MEN 10627 (1 micromol kg(-1) i.v.) or the histamine H1-receptor antagonist, diphenhydramine (34.5 micromol kg(-1) i.v.). However, the [Sar9,Met(O2)11]substance P-induced PPE was blocked by the previous administration of the peptide tachykinin NK-1 receptor antagonist FK 888 or by the non-peptide antagonist SR 140333, yielding ED50 values of 1.1 +/- 0.2 and 0.01 +/- 0.004 micromol kg(-1) i.v., respectively. 3. The tachykinin NK-2 or NK-3 receptor agonists [beta-Ala8]neurokinin A (4-10) or [MePhe7]neurokinin B, respectively, produced a weak PPE at high doses. The effect of [MePhe7]neurokinin B-induced PPE was inhibited by SR 140333. 4. In the guinea-pig isolated oesophageal sphincter, [Sar9,Met(O2)11]substance P did not exert any contractile effect up to 10 microM. The selective tachykinin NK-2 receptor agonist ([beta-Ala8]neurokinin A (4-10), produced concentration-dependent contractions (pD2 = 7.6 +/- 0.03) which were inhibited by the selective tachykinin NK-2 receptor antagonist, MEN 10627 (pA2 = 8.6 +/- 0.1). Also, the tachykinin NK-3 receptor selective agonist [MePhe7]neurokinin B induced concentration-dependent contractile responses, but these responses were inhibited by MEN 10627. 5. Altogether, these data indicate that the stimulation of tachykinin NK-1 receptor produces a vascular inflammatory response, while activation of tachykinin NK-2 receptors mediate the contraction of the guinea-pig oesophageal sphincter.

Differential activation of the epithelial and smooth muscle NK1 receptors by synthetic tachykinin agonists in guinea-pig trachea.

1. The presence of tachykinin NK1 receptors have been shown in the epithelium and smooth muscle of guinea-pig airways. Previous data showed that substance P (SP), and the NK1 receptor agonist, [Sar9, Met (O2)11]-SP, relax guinea-pig tracheal tube preparations by stimulation of epithelial NK1 receptors and via nitric oxide (NO) release. However, the selective tachykinin NK1 receptor agonist, septide, was unable to produce this effect. The aim of the present study was to investigate the ability of a series of SP analogues to stimulate NK1 receptors of guinea-pig airway epithelium. 2. Isometric tension was recorded in isolated tracheal tube preparations in which compounds were administered intraluminally in the presence of phosphoramidon, indomethacin (both 1 microM) and the tachykinin NK2 receptor antagonist, SR 48,968 ((S)-N-methyl N-(4-acetyl-amino-4-phenylpiperidino)-2-(3,4-dichlorophenyl)butyl)benzam ide) (0.1 microM). Cumulative concentration-response curves were obtained in preparations under resting tone or in preparations precontracted with acetylcholine (ACh, 10 microM). 3. Contractile responses to low concentrations (0.1-10 nM) of substance P (SP) and the selective agonist of NK1 receptors, [Pro9]-SP. in non precontracted tracheae were higher in preparations pretreated with the NO-synthase inhibitor, NG-monomethyl L-arginine (L-NMMA, 100 microM) than in preparations pretreated with its inactive enantiomer D-NMMA (100 microM). Tracheal tube preparations precontracted with ACh and pretreated with D-NMMA were relaxed by low concentrations of SP and [Pro9]-SP (0.1-10 nM). In contrast, after pretreatment with L-NMMA, SP and [Pro9]-SP contracted tracheae at all the concentrations tested. 4. Concentration-response curves to the NK1 receptor agonists, SP methyl ester, [Apa9-10]-SP and [pGlu6] SP (6-11) obtained in non-precontracted tracheae were similar in the presence of either D-NMMA or L-NMMA. SP methyl ester, [Apa9-10]-SP and [pGlu6] SP (6-11) did not produce any relaxation, but instead, cause contractions in tracheal tube preparations precontracted with ACh and pretreated with D-NMMA. Concentration-response curves produced by all these agonists were similar in preparations precontracted with ACh and pretreated with L-NMMA or D-NMMA. 5. In guinea-pig tracheal tube preparations two groups of NK1 receptor agonists can be distinguished: one group, including [Pro9]-SP, stimulator epithelial NK1 receptors, the other group, including SP methyl ester, [Apa9-10]-SP and [pGlu6] SP (6-11), does not. One possible explanation for these findings and for the existence of compounds with a peculiar 'septide-like' pharmacological profile in the guinea-pig trachea could be the recently proposed phenomenon referred to as 'agonist-directed receptor trafficking'.

Stimulation of tachykinin NK-3 receptors in the nucleus basalis magnocellularis reduces alcohol intake in rats.

Injections in the nucleus basalis magnocellularis (NBM) of the tachykinin (TK) NK-3 receptor agonist [Asp5,6,MePhe8]substance P(5-11), also referred to as amino-senktide (NH2-SENK), markedly reduced alcohol intake in genetically selected alcohol-preferring rats, offered 10% ethanol 2 h/day. The threshold dose in the NBM was 0.5 ng/site, while neither 1 nor 10 ng/rat of NH2-SENK inhibited alcohol intake following administration into the lateral ventricle. Injection of NH2-SENK, 25 ng/site, in the NBM did not modify water or food intake in water deprived rats, providing evidence for the behavioral selectivity of the effect on ethanol intake. The selective TK NK-3 receptor antagonist, R-820, injected in the NBM at the dose of 1000 ng/site 5 min before NH2-SENK 5 ng/site, significantly reduced the effect of NH2-SENK. The selective TK NK-1 receptor agonist [Sar9,Met(O2)11]substance P inhibited alcohol intake following injection in the NBM only at 25 ng/site; but the same dose induced marked grooming and inhibited also water intake in water deprived rats. The present results confirm that TK NK-3, but not NK-1, receptor agonists selectively inhibit ethanol intake in alcohol-preferring rats and suggest that the NBM is a site of action for their effect.

Evidence for the involvement of bradykinin in chemically-evoked cystitis in anaesthetized rats

The effect of Hoe 140, a potent bradykinin B2 receptor antagonist, on the micturition reflex and detrusor hyperreflexia induced by chemical cystitis has been investigated in anaesthetized rats. Hoe 140 (1-100 nmol/kg i.v.) produced a dose-dependent blockade of the contraction of the rat urinary bladder induced by i.v. administration of bradykinin (100 nmol/kg) without affecting the response produced by the selective tachykinin NK-1 receptor agonist, [Sar9] substance P (SP) sulfone (1 nmol/kg i.v.). At doses which produce selective and long-lasting blockade of bradykinin receptors in the urinary bladder, Hoe 140 did not modify urodynamic parameters in normal rats. Intravesical instillation of xylene in female rats decreased bladder capacity and increased micturition frequency. These effects also occurred in rats pretreated with capsaicin as adults. Hoe 140 did not modify xylene-induced cystitis. Intraperitoneal administration of cyclophosphamide (150 mg/kg, 48 h before) decreased bladder capacity and increased micturition frequency. These effects of cyclophosphamide were abolished in rats pretreated with capsaicin as adults. Hoe 140 increased bladder capacity and decreased micturition frequency in rats pretreated with cyclophosphamide. Addition of bradykinin (10 mumol/l) to the medium in the superfused rat urinary bladder preparation evoked a prompt increase in the outflow of calcitonin gene-related peptide like immunoreactivity (CGRP-LI). Hoe 140 (3 mumol/l) inhibited (by about 50%) the CGRP-LI out-flow stimulated by bradykinin. These findings demonstrate the participation of bradykinin, through B2 receptors, in the genesis of detrusor hyperreflexia during cyclophosphamide-induced cystitis.(ABSTRACT TRUNCATED AT 250 WORDS)