NK2 tachykinin receptors and contraction of circular muscle of the human colon: characterization of the NK2 receptor subtype

doi:10.1016/0014-2999(91)90892-T

European Journal of Pharmacology

Volume 203, Issue 3, 22 October 1991, Pages 365-370

https://doi.org/10.1016/0014-2999(91)90892-T Get rights and content

Abstract

The contractile effect of substance P, neurokinin A, receptor selective agonists for tachykinin receptors and NK₂ tachykinin receptor antagonists was investigated in mucosa-free circular strips of the human isolated colon. Neurokinin A and substance P produced concentration-dependent contractions which approached 80–90% of the maximal response to carbachol. Neurokinin A was about 370 times more potent than substance P. The action of neurokinin A and substance P was not modified by peptidase inhibitors (bestatin, captopril and thiorphan, 1 μM each). The NK₂ receptor selective agonist, [β3-Ala⁸]neurokinin A-(4–10) closely mimicked the response to neurokinin A while NK₁ and NK₃ receptor selective agonists were active only at μM concentrations. The pseudopeptide, MDL 28,564, which is one of the most selective NK₂ ligands available, behaved as a full agonist. Responses to [β-Ala⁸]neurokinin A were antagonized by NK₂ receptor selective antagonists, with the rank order of potency MEN 10,376 > L 659,877 > R 396. These data indicate that NK₂ tachykinin receptors play a dominant role in determining the contraction of the circular muscle of the human colon to peptides of this family. The NK₂ receptor subtype responsible for this effect belongs to the same subtype (NK_2A) previously identified in the rabbit pulmonary artery and guinea-pig bronchi.

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Impaired colonic motility and reduction in tachykinin signalling in the aged mouse
2014, Experimental Gerontology
Citation Excerpt :
NK2 receptors are predominantly located on longitudinal and circular smooth muscle cells in both mice (Dickson et al., 2010; Matsumoto et al., 2009) and humans (Giuliani et al., 1991; Jaafari et al., 2007) and provide the main receptor through which electrical field stimulation (EFS)-evoked release of tachykinins causes smooth muscle contraction. In human colons, application of NK2 receptor agonists induced contractions, while selective NK2 antagonists were capable of almost completely blocking EFS-evoked colonic contractions (Giuliani et al., 1991; Nakamura et al., 2011). These data are consistent with NK2 agonists having a pro-kinetic effect in this part of the GI tract.
Ageing is associated with an increased incidence of constipation in humans. The contribution that the ageing process makes to this condition is unclear. The aim of this study was to determine the effects of age on faecal output and colonic motility in male C57BL/6J mice and to determine the role that altered tachykinin signalling plays in this process. Total faecal output recorded over a 24 h period decreased with age due to a reduction in the number of pellets produced and their water content. These changes occurred in the absence of any significant change in food and water intake. There was an increase in the amount of faecal matter stored in the isolated colon with age which caused a proportional increase in colonic length. Analysis of colonic motility using an artificial pellet demonstrated that pellets moved in a stepwise fashion through the colon. There was an age-related increase in pellet transit time due to decreases in the step distance, velocity, and frequency of stepwise movements. These changes were reversed using the neurokinin 2 (NK₂) receptor agonist neurokinin A. Addition of the NK₂receptor antagonist GR159897 significantly increased transit time in the young animals by decreasing step distance, velocity and frequency, but was without effect in the aged colon. In summary, the ageing C57BL/6J mouse shows an impaired motility phenotype. These effects appear, at least in part, to be due to an attenuation of tachykinin signalling via NK₂ receptors.
Characterization of ibodutant at NK<inf>2</inf> receptor in human colon
2013, European Journal of Pharmacology
We have characterized the pharmacological profile of the nonpeptide tachykinin NK₂ receptor antagonist ibodutant (MEN15596) through radioligand binding and contractility assays in the human colon smooth muscle. The antagonist affinity of ibodutant was evaluated through concentration-dependent inhibition curves at the [¹²⁵I]NKA specific binding by using membranes prepared from human colon smooth muscle. In this assay the affinity of ibodutant (pK_i 9.9) was compared to that of other two selective NK₂ receptor antagonists, nepadutant (pK_i 8.4) and saredutant (pK_i 9.2). The antagonist potency of ibodutant was evaluated towards the [βAla⁸]NKA(4-10)-mediated contractions of human colon smooth muscle strips. In this assay ibodutant (3, 10, 30 and 100 nM) induced a concentration-dependent rightward shift of the [βAla⁸]NKA(4-10) concentration-response curves without depressing the maximal contractile effect. The analysis of the curves yielded a Schild-plot linear regression with a slope not different from unity (1.02), thus indicating a surmountable antagonist behavior. The calculated apparent antagonist potency as pK_B value was 9.1. No sex related differences were observed in NK₂ receptor pharmacology for [βAla⁸]NKA(4-10) or ibodutant in colonic strips obtained from male or female patients. Reversibility experiments of tachykinin NK₂ receptor blockade indicated that the inhibition of the agonist-induced contractions in preparations pre-exposed to ibodutant, and afterwards subjected to repeated washing cycles remained almost constant showing no sign of recovery during the 3 h observation period. Overall, the present study indicates ibodutant as a potent tachykinin NK₂ receptor antagonist in the human colon tissue, also endowed with a persistent duration of action.
Establishment and validation of a rabbit model for in vivo pharmacodynamic screening of tachykinin NK<inf>2</inf> antagonists
2012, Journal of Pharmacological Sciences
We attempted to establish and validate an in vivo pharmacodynamic (PD) rabbit model to screen tachykinin NK₂ receptor (NK₂-R) antagonists using pharmacological and pharmacokinetic (PK)/PD analyses. Under urethane anesthesia, changes in intracolonic pressure associated with intravenous (i.v.) administration of a selective NK₂-R agonist, βAla⁸-neurokinin A(4-10) (βA-NKA), was monitored as a PD marker. The analgesic effects of NK₂-R antagonists were evaluated by monitoring visceromotor response (VMR) to colorectal distension in a rabbit model of visceral hypersensitivity induced by intracolonic treatment of acetic acid. Intravenous administration of βA-NKA induced transient colonic contractions dose-dependently, which were inhibited by the selective NK₂-R antagonists in dose- and/or plasma concentration–dependent manners. The correlation between PD inhibition and plasma concentration normalized with the corresponding in vitro binding affinity was relatively high (r² = 0.61). Furthermore, the minimum effective doses on the VMR and ID₅₀ values calculated in the PD model were highly correlated (r² = 0.74). In conclusion, we newly established and validated a rabbit model of agonist-induced colonic contractions as a screening tool for NK₂-R antagonists. In a drug discovery process, this PD model could enhance the therapeutic candidate selection for irritable bowel syndrome, pharmacologically connecting in vitro affinity for NK₂-R with in vivo therapeutic efficacy.
Tachykinins and Neurogenic Inflammation at Visceral Level
2009, NeuroImmune Biology
Citation Excerpt :
In addition, stimulation of tachykinin receptors (mainly of the NK3 type) present on gastrointestinal neurons may induce indirect contractile responses mediated by either acetylcholine [198] and/or tachykinins themselves [199,200]. Most of spasmogenic effects produced by tachykinins in human gastrointestinal organs such as the ileum [200], colon [201], and esophagus [202] are mediated by NK2 receptors, while NK1 receptors have been reported to contribute tachykinin-induced contraction in the circular muscle of the human ileum [200]. Several in vitro studies were aimed at investigating the endogenous mediators of both excitatory and inhibitory neurotransmission in the human intestine [203–205], biliary tract [206], and esophagus [207].
Tachykinin-containing projections of capsaicin-sensitive primary afferent neurons widely distribute to visceral organs of the respiratory, gastrointestinal, and genitourinary systems. At this level, tachykinins, along with calcitonin gene-related peptide and other neuropeptides, can be released by adequate stimuli having pathological rather than physiological relevance. Such stimuli may represent chemical irritants to the respiratory tree or alimentary tract, or noxious agents secreted into the urinary system. Tachykinins produced in the visceral organs are part of the responses obtained at somatic level by antidromic activation of capsaicin-sensitive nerve terminals and collectively known as “neurogenic inflammation”: that is, increase in vascular permeability and plasma protein leakage followed by edema. In addition, tachykinins produced at visceral level elicit smooth muscle contraction, neuronal stimulation, mucus secretion, and recruitment/activation of immune cells. The physiological significance of these effects is that to afford protection toward chemical irritants or noxious stimuli by facilitating their removal from the body. Nonetheless, a large body of preclinical evidence exists indicating that tachykinins participate to the genesis and/or maintenance of symptoms accompanying various human diseases, such as asthma/bronchial hyperreactivity, cystitis of various etiologies, inflammatory bowel diseases, and irritable bowel syndrome. Tachykinin receptor antagonists, which are proved to prevent/reduce tachykinin-mediated effects in experimental animal models of these pathologies, are expected to afford therapeutically relevant effects in humans.
MEN15596, a novel nonpeptide tachykinin NK<inf>2</inf> receptor antagonist
2006, European Journal of Pharmacology
The pharmacological profile of MEN15596 or (6-methyl-benzo[b]thiophene-2-carboxylic acid [1-(2-phenyl-1R-{[1-(tetrahydropyran-4-ylmethyl)-piperidin-4-ylmethyl]-carbamoyl}-ethylcarbamoyl)-cyclopentyl]-amide), a novel potent and selective tachykinin NK₂ receptor antagonist endowed with oral activity, is described. At the human recombinant tachykinin NK₂ receptor, MEN15596 showed subnanomolar affinity (pK_i 10.1) and potently antagonized (pK_B 9.1) the neurokinin A-induced intracellular calcium release. MEN15596 selectivity for the tachykinin NK₂ receptor was assessed by binding studies at the recombinant tachykinin NK₁ (pK_i 6.1) and NK₃ (pK_i 6.4) receptors, and at a number of 34 molecular targets including receptors, transporters and ion channels. In isolated smooth muscle preparations MEN15596 showed a marked species selectivity at the tachykinin NK₂ receptor with the highest antagonist potency in guinea-pig colon, human and pig bladder (pK_B 9.3, 9.2 and 8.8, respectively) whereas it was three orders of magnitude less potent in the rat and mouse urinary bladder (pK_B 6.3 and 5.8, respectively). In agreement with binding experiments, MEN15596 showed low potency in blocking selective NK₁ or NK₃ receptor agonist-induced contractions of guinea-pig ileum preparations (pA₂ ≤ 6). In anaesthetized guinea-pigs, MEN15596 inhibited in a dose-related and persistent manner colon contractions induced by the selective tachykinin NK₂ receptor agonist, [βAla⁸]neurokinin A(4–10) (3 nmol/kg i.v.), either after intravenous (ED₅₀ 0.18 μmol/kg), intraduodenal (ED₅₀ 3.16 μmol/kg) or oral administration (10–30 μmol/kg) without affecting, at 3 μmol/kg, i.v., the colonic contractions produced by the NK₁ receptor selective agonist [Sar⁹]substance P sulfone (3 nmol/kg i.v.). In addition MEN15596 was effective in inhibiting bronchoconstriction produced by i.v. administration of [βAla⁸]neurokinin A(4–10). Overall the results indicate that MEN15596 is a potent and selective tachykinin NK₂ receptor antagonist possessing high affinity and potency for guinea-pig, pig and human receptor, long duration of action in in vivo experiments and good oral bioavailability.
Tachykinins and tachykinin receptors in the gut, with special reference to NK2 receptors in human
2006, Autonomic Neuroscience: Basic and Clinical
Tachykinins (TKs), substance P (SP), neurokinin A (NKA) and B (NKB) are important peptide modulators of intestinal motility in animal species studied so far, including humans. Modulation of motility by TKs can occur at various levels, since these peptides are expressed in cholinergic excitatory motor neurons projecting to both circular and longitudinal muscle, interneurons, and intramural and extramural sensory neurons. The effects of SP, NKA and NKB are preferentially mediated through the stimulation of NK1, NK2 and NK3 receptors, respectively; however, the selectivity of natural TKs for their preferred receptors is relative. In addition, SP and NKA are expressed in similar quantities in the human intestine and adequate stimuli can release similar amount of these TKs from enteric nerves. Furthermore, a single anatomical substrate can express more than one TK receptor type, so that the blockade of a single receptor type may not reveal functional effects in integrated models of motility. In isolated human small intestine and colon circular muscle strips, both NK1 and NK2 receptors mediate contractile effects. Indeed, in the human small intestine, smooth muscle electrical and motor events induced by electrical field stimulation (EFS) can involve either or both NK1 and NK2 receptors or these latter receptors predominantly, depending on the experimental conditions. In contrast, in the human colonic smooth muscle, only the NK2 receptor-mediated component of the response to EFS is prominent and some evidence would suggest that this component is the main excitatory motor mechanism at this level. Furthermore, a NK2 receptor-mediated secretory component in the human colonic mucosa has been recently demonstrated. Thus, it could be speculated that the blockade of both NK1 and NK2 receptors will be necessary to antagonise motor effects induced by exogenous administration or endogenous release of TKs in the small intestine, whereas the blockade of the NK2 receptors would be sufficient to disrupt physiological motor and, possibly, secretory activity at the colonic level. Available evidence indicates that, in healthy volunteers, the infusion of NKA (25 pmol/kg/min i.v.) stimulated small intestine motility and precipitated a series of intestinal and non-intestinal adverse events. Nepadutant (8 mg i.v.), a selective NK2 receptor antagonist, antagonised small intestine motility induced by NKA and prevented associated intestinal adverse events. In another study, the same dose of nepadutant increased colo-rectal compliance during isobaric balloon distension in healthy volunteers pretreated with a glycerol enema, disclosing a NK2 receptor-mediated component in the regulation of colonic smooth muscle tone. However, the prolonged blockade of NK2 receptors by nepadutant (16 mg i.v. b.i.d. for 8 days) did not affect bowel habits, neither in term of movements nor of stool consistency. Altogether, these results indicate that, even when there is a significant redundance in the effects of TKs and in the role of their receptors, the selective blockade of tachykinin NK2 receptors can have functional consequences on human intestinal motility and perception, but this can occur without the disruption of the physiological functions.

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NK2 tachykinin receptors and contraction of circular muscle of the human colon: characterization of the NK2 receptor subtype

Abstract

Neuroscience

Life Sci. Pharmacol. Lett

Neurochem. Int.

Eur. J. Pharmacol.

Neuropeptides

Gastroenterology

Gastroenterology

Ncuroscience

Ann. N.Y. Acad. Sci.

Eur. J. Pharmacol.

Peptides

Gastroenterology

Reg. Pept.

NK₂ tachykinin receptors and contraction of circular muscle of the human colon: characterization of the NK₂ receptor subtype