Tachykinin receptor types: Classification and membrane signalling mechanisms

Cyclosporin A is a substance P (tachykinin NK1) receptor antagonist

The immunosuppressive cyclic undecapeptide, cyclosporin A, inhibited the binding of [125I]substance P to tachykinin NK1 receptors expressed by human IM-9 lymphoblastoid cells, U-373 MG human astrocytoma cells and guinea pig lung parenchyma with IC50 values of 425 +/- 58, 783 +/- 180, and 784 +/- 163 nM respectively. The dihydro derivative of cyclosporin A (dihydro-cyclosporin A) was an equally effective inhibitor, but the O-acetylated derivative (cyclosporin A-OAc) was 3-4 fold less potent. The cyclosporin compounds also inhibited [125I]neurokinin A binding to human NK2 receptors with potencies slightly less than at NK1 sites. In contrast, they were 8-20-fold less effective inhibitors of [125I]MePhe7-neurokinin B binding to guinea pig NK3 receptors (p < 0.001). Thus, the cyclosporin A compounds showed selectivity for NK1 and NK2 receptors. The structure-activity pattern for the effects of cyclosporin A compounds at tachykinin receptors differs from the pattern previously described for their immunosuppressive activity. All three compounds inhibited substance P induced interleukin-6 (IL-6) secretion from U-373 MG astrocytoma cells with potencies similar to their NK1 receptor binding affinities. In addition, cyclosporin A blocked substance P induced phosphatidylinositol (PI) turnover in U-373 MG cells without blocking the corresponding response to histamine. This novel pharmacological profile of the cyclosporin A compounds as NK1 receptor antagonists does not appear to correlate with other known in vitro cyclosporin A functions.

Antinociceptive profiles of non-peptidergic neurokinin1 and neurokinin2 receptor antagonists: a comparison to other classes of antinociceptive agent

This study compared the antinociceptive properties of systemic administration of selective, non-peptidergic antagonists at neurokinin (NK1 and NK2) receptors to those of other classes of antinociceptive agent. (All doses are in mg/kg.) In mice, the NK1 antagonist, CP 99,994, preferentially (inhibitory dose50 (ID50) = 4.4) inhibited the late phase (LP) as compared to the early phase (EP) (16.1) of formalin-induced licking (FIL). A high dose (17.6) elicited ataxia in the rotarod test. Acetic acid-induced writhing was reduced at intermediate doses (10.0) whereas the tail-flick (TF) response to thermal and mechanical stimuli was inhibited only at high doses (22.7 and 17.7, respectively). Modulation of stimulus intensity did not modify the influence of CP 99,994 upon the response to heat. A similar pattern of data was acquired with RP 67,580, although this NK1 antagonist more potently inhibited writhing (2.8). In contrast, RP 68,651, the inactive isomer of RP 67,580, neither reduced the LP of FIL nor modified writhing indicating that these actions of RP 67,580 were stereospecific. Three further NK1 antagonists, SR 140,333, WIN 51,708 and WIN 62,577, likewise inhibited the LP of FIL and failed to modify the TF response at non-ataxic doses. Further, SR 140,333 (0.5) and WIN 51,708 (1.4) were potent ligands in the writhing procedure. The NK2 antagonist, SR 48,966, mimicked NK1 antagonists in preferentially inhibiting the LP (7.7) as compared to the EP (26.9) of FIL. Further, only at doses higher than those evoking ataxia (20.9) did SR 48,968 modify the TF response (36.5 and 32.0 for heat and pressure, respectively). However, it differed to NK1 antagonists in being inactive in the writhing test (> 40.0). In comparison to these NK1 and NK2 antagonists, the mu-opioid agonists (morphine and fentanyl) and kappa-opioid agonists (enadoline and U 69,593) equipotently inhibited all nociceptive responses at doses not provoking ataxia. While the glycine B receptor partial agonist, (+)-HA 966, selectively blocked the LP of FIL and did not evoke ataxia, the NMDA receptor channel blocker, (+)-MK 801, elicited antinociception only at doses close to those provoking ataxia. Finally, the NSAIDs, indomethacin and ibuprofen, the BK2 antagonist, Hoe 140 and the nitric oxide synthase (NOS) inhibitors, L-NAME and 7 nitroindazole, inhibited the LP (but not the EP) of FIL and (except for L-NAME) also reduced writhing: in contrast, they did not evoke ataxia and were inactive in the TF procedures.(ABSTRACT TRUNCATED AT 400 WORDS)

Substance P-induced inflammatory responses in guinea-pig skin: the effect of specific NK1 receptor antagonists and the role of endogenous mediators

1. The sensory neuropeptide substance P (SP), when released from sensory nerves, has been implicated in the development of neurogenic inflammation. In the present study, using an in vivo model system, we have characterized and investigated the mechanisms underlying SP-induced leukocyte accumulation and oedema formation in the guinea-pig. 2. Intradermally injected SP (i.d., 10(-13) - 10(-9) mol per site), induced a dose- and time-dependent accumulation of 111In-neutrophils, 111In-eosinophils and oedema formation as measured by the local accumulation of i.v. injected 125I-albumin. The leukocyte accumulation evoked by SP was significant at 10(-10) and 10(-9) mol per site, whereas oedema formation was significant at the lowest dose tested (10(-13) mol per site). 3. The NK1 receptor antagonists, CP-96,345 (1 mg kg-1, i.v.) and RP-67,580 (10 micrograms per site, i.d.), significantly attenuated the oedema formation induced by the lower doses of SP. Oedema formation and leukocyte accumulation induced by 10(-9) mol per site SP were unaffected by either antagonist. 4. SP-elicited responses were not significantly affected by the platelet activating factor (PAF) receptor antagonist, UK-74,505 (2.5 mg kg-1, i.v.) or the H1 histamine receptor antagonist, chlorpheniramine (10(-8) mol per site, i.d.). However, the 111In-eosinophil accumulation, but not the 111In-neutrophil accumulation or oedema formation, induced by SP was significantly inhibited by the specific 5-lipoxygenase (5-LO) inhibitor, ZM-230,487 (10(-8) mol per site, i.d.). 5. The accumulation of both 111 In-neutrophils and 111 In-eosinophils induced by SP was abolished in guinea-pigs treated i.v. with an anti-CD18 monoclonal antibody 6.5E F(ab')2 (2.5 mg kg-1). The oedema response was unaffected in these animals.6. These results suggest that SP-induced inflammatory events may be mediated via two mechanisms involving NK1 receptor-dependent and independent pathways. Oedema formation induced by the lower doses of SP may be mediated via the direct activation of NK1 receptors whilst, at higher doses, oedema formation and leukocyte accumulation may be mediated via the release of secondary mediators, possibly mast cell derived, with 5-LO products playing an important role in the leukocyte infiltration. The leukocyte accumulation, but not the oedema induced by SP, is dependent on the expression of the CD18antigen on leukocytes.

Effects of the tachykinin NK1 receptor antagonist, RP 67580, on central cardiovascular and behavioural effects of substance P, neurokinin A and neurokinin B

1. We have investigated the effects of the non-peptide NK1 tachykinin receptor antagonist, RP 67580, and its inactive enantiomer, RP 68651, on the cardiovascular and behavioural responses to substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) injected intracerebroventricularly (i.c.v.) in conscious rats. 2. The SP and NKA (25 pmol)-induced increases in blood pressure (BP) and heart rate (HR) were of the same magnitude. The cardiovascular responses to both peptides were associated with excessive grooming behaviour and wet dog shakes (WDS). Relative to SP, NKA was weaker in inducing hindquarter grooming (HG), but more effective in eliciting WDS. The cardiovascular response to NKB (50 pmol) comprised an increase in BP and HR, while the behavioural response was weak. 3. RP 67580 (100 pmol), injected 10 or 30 min prior to SP, effectively inhibited the cardiovascular and behavioural responses to the peptide whereas lower doses were ineffective. Pretreatment with 500 pmol of RP 67580, 10 or 30 min prior to SP, reduced the BP response. Of the behavioural manifestations, only face washing was attenuated when the antagonist was injected 10 min before SP. At 2500 pmol, the antagonist exaggerated the BP response to the peptide without affecting the behavioural response. RP 68651 (100 or 2500 pmol) did not modify the central responses to SP. 4. Neither RP 67580 nor RP 68651 (100 pmol), affected the cardiovascular and behavioural responses to NKA or NKB. 5. Our results indicate that RP 67580 is a selective and high affinity antagonist at central NK1 tachykinin receptors in the rat.

Effects of substance P on cardiovascular regulation in the rabbit

The effect of substance P on blood pressure and aortic reflex was investigated in rabbits. Microinjections of substance P and Sar9, Met(O2)11-SP (a selective NK1-receptor agonist) into the floor of the fourth ventricle led to a dose-dependent increase of blood pressure and a sharp enhancement of the baroreflex. These effects were abolished by pretreatment with SR 140333 (a selective NK1-receptor antagonist). Intraventricular injection of the antagonist alone significantly decreased the amplitude of the aortic reflex. After bivagotomy, the amplitude of the parasympathetic component of the baroreflex decreased dramatically and substance P injections were no longer effective. Our results demonstrate that substance P activation of NK1 receptors plays a major role in the modulation of the parasympathetic component of the baroceptor reflex.

The role of neuropeptides in learning: focus on the neurokinin substance P

The neurokinin substance P (SP) can have neurotrophic as well as memory-promoting effects. The study of its mechanisms may provide new insights into processes underlying learning and neurodegenerative disorders. Our work shows that SP, when applied peripherally (i.p.), promotes memory and is reinforcing at the same dose of 37 nmol/kg. Most important, however, is the finding that these effects seemed to be encoded by different SP-sequences, since the N-terminal SP1-7 (185 nmol/kg) enhanced memory, whereas C-terminal hepta- and hexapeptide sequences of SP proved to be reinforcing in a dose equimolar to SP. These differential behavioral effects were paralleled by selective and site-specific changes in dopamine (DA) activity, as both SP and its C-, but not N-terminus, increased extracellular DA in the nucleus accumbens (NAc), but not in the neostriatum. The neurochemical changes lasted at least 2 h after injection. Direct application of SP (0.74 pmol) into the region of the nucleus basalis magnocellularis (NBM) was also memory-promoting and reinforcing, and again, these effects were differentially produced by the N-terminus and C-terminus, supporting the proposed structure-activity relationship for SP's effects on memory and reinforcement. In addition, it was found that a single injection of SP into the NBM led to an increase of extracellular DA in the contralateral NAc. This effect of SP was observed only in those animals where SP was reinforcing, providing evidence for a lateralized relationship between reinforcement induced by injection of SP into the NBM and DA activity in the NAc. Furthermore, the outcome of a series of experiments suggests, that SP may not only be considered to have memory-promoting effects in normal animals, but can also improve functional recovery after unilateral 6-OHDA lesion of the substantia nigra and after lesions of the hippocampus, and can counteract age-related performance deficits.

Characterization and autoradiographic mapping of [3H]CP96,345, a nonpeptide selective NK1 receptor antagonist in guinea pig lung

We have studied binding and distribution of NK1 receptors in guinea pig lung using [3H]CP96,345. Kinetic studies showed that specific binding of [3H]CP96,345 was rapid and reversible, giving a kinetic dissociation constant (Kd) of 0.28 +/- 0.05 nM. The specific binding was also saturable and Scatchard analysis indicated a single class of binding site with an equilibrium Kd of 0.12 +/- 0.03 nM and maximum binding capacity (Bmax) of 107.0 +/- 10.3 fmol/mg of protein. Competition studies showed the rank order of affinity for agonists and antagonists as follows: SP > NKA = septide >> NKB = senktide; CP96,345 > FK888 > FK224 > L668169. NK3 agonists, NK2-selective antagonists, and a calcium channel blocker, diltiazem, showed no displacement, indicating high selectivity for NK1 receptors. Autoradiographic mapping showed specific labeling over airway smooth muscle from central to peripheral airways, submucosal glands, and nerve fibers of trachea. The labeling of airway epithelium was increased with diminishing size of airways. Pulmonary blood vessels were also moderately labeled and there was sparse labeling over alveolar walls. [3H]CP96,345 may provide a useful tool to evaluate NK1 receptor expression in peripheral organs.

Different mechanism of tachykinin NK2 receptor blockade by SR 48968 and MEN 10,627 in the guinea-pig isolated gallbladder and colon

The mechanism of action of the tachykinin NK2 receptor antagonists, SR 48968 ((S)-N-methyl-N[4-acetylamino-4-phenyl-piperidino)-2-(3,4- dichlorophenyl)butyl]benzamide) and MEN 10,627 (cyclo[(Met-Asp-Trp-Phe-Dap-Leu) cyclo (2 beta-5 beta)]), was compared in the guinea-pig isolated gallbladder and circular muscle of proximal colon by using neurokinin A and [beta Ala8]neurokinin A-(4-10) as agonists. The experiments performed with colon were in the presence of the tachykinin NK1 receptor-selective antagonist, (+/-)-CP-96,345 ([2-(diphenylmethyl)-N-[(2-methoxyphenyl)-methyl]-1- azabicyclo[2,2,2]octan-3-amine]). SR 48968 caused an insurmountable antagonism of tachykinin NK2 receptor-mediated contraction in both preparations; its blockade was essentially irreversible, since it was not reversed by washout (up to 2 h) and was increased by prolonging the incubation from 15 to 120 min. In contrast, MEN 10,627 produced simple competitive antagonism, which was time-independent and fully reversible in both preparations. In both preparations, the simultaneous administration of SR 48968 and MEN 10,627 produced an intermediate antagonism of the responses to the agonists, as compared to the antagonism produced by each antagonist alone. The present results are discussed in the light of the reported interaction of SR 48968 with tachykinin NK2 receptors at a recognition epitope distinct from that of agonist(s).

'Sensory-efferent' neural control of mucus secretion: characterization using tachykinin receptor antagonists in ferret trachea in vitro

1. We characterized the tachykinin receptor(s) mediating 'sensory-efferent' neural control of release of 35SO4-labelled macromolecules (mucus) from ferret trachea in vitro in Ussing chambers using selective tachykinin antagonists. Secretion was induced by substance P (SP), neurokinin A (NKA), capsaicin, the NK1 tachykinin receptor agonist [Sar9, Met(O2)11]substance P ([Sar9]SP), or acetylcholine (ACh), or by electrical stimulation of nerves. Antagonists used were FK888 and L-668,169, selective for the NK1 receptor, SR 48968, selective for the NK2 receptor, and FK224, a dual antagonist at NK1 and NK2 receptors. The selectivity of FK888 and SR 48968 was examined on NKA-induced contraction of ferret tracheal smooth muscle in vitro. 2. SP (1 microM) increased mucus secretion by 695% above vehicle controls. FK888 (0.1 microM-30 microM) inhibited SP-induced secretion in a dose-dependent manner, with complete inhibition at 10 microM and an IC50 of 1 microM. L-668,169 (1 microM) also completely inhibited SP-induced secretion. 3. NKA (1 microM) significantly increased mucus secretion by 271% above baseline, a response which was completely inhibited by FK888 (10 microM) or L-668,169 (microM). Secretion induced by ACh (10 microM: 317% above baseline) was not inhibited by FK888 but was inhibited by atropine. Capsaicin (10 microM)-induced secretion (456% above vehicle controls) was significantly inhibited by FK888 and by L-668,169 (111% and 103% inhibition respectively). 4. Electrical stimulation (50 V, 10 Hz, 0.5 ms, 5 min) increased mucus output above baseline (increased by 12 to 26 fold), a response blocked by tetrodotoxin (0.1 microM). FK888 (10 microM) inhibited the increase in secretion due to electrical stimulation by 47%. Atropine, propranolol and phentolamine in combination(APP) inhibited the response to electrical stimulation by 48%. The remaining NANC response, i.e. in the presence of APP, was further reduced by 66% with FK888. FK224 (10 microM) inhibited neurally evoked secretion by 73%. SR 48968 (0.1 fLM) had no effect on electrically-stimulated or [Sar9]SP-induced secretion.5. NKA (10nM- 1O microM: in the presence of DMSO control vehicle) induced tracheal smooth muscle contraction in a concentration-dependent manner with a maximal contraction of 30% of the maximal response to ACh (10 mM) and an ECm of 0.3 JAM. SR 48968 (0.1 microM in DMSO) inhibited the NKA induced contraction whereas FK888 did not. Neither antagonist had any inhibitory effect on ACh induced contraction.6. We conclude that 'sensory-efferent' neurogenic mucus secretion in ferret trachea in vitro is mediated via tachykinin NK, receptors with no involvement of NK2 receptors. Potent and selective tachykinin antagonists may have therapeutic potential in bronchial diseases such as asthma and chronic bronchitis in which neurogenic mucus hypersecretion may be aetiologically important.

Specialization of tachykinin NK1 and NK2 receptors in producing fast and slow atropine-resistant neurotransmission to the circular muscle of the guinea-pig colon

We studied the relative contribution of tachykinin NK1 and NK2 receptors in producing nonadrenergic noncholinergic excitation of the circular muscle of the guinea-pig proximal colon in response to electrical field stimulation. All experiments were performed in the presence of atropine, guanethidine, indomethacin, apamin and L-nitroarginine. In organ bath experiments, electrical stimulation produced a tetrodotoxin-sensitive frequency-dependent contraction. The NK1 receptor antagonists, FK 888 (1-10 microM) and GR 82,334 (0.3-3 microM) markedly reduced but did not abolish the nonadrenergic noncholinergic response. The NK2 receptor antagonist, GR 94,800 (0.3-3 microM) was partly effective at 3 microM. The combined administration of FK 888 (10 microM) and GR 94,800 (3 microM) or GR 82,334 and GR 94,800 abolished the nonadrenergic noncholinergic contraction. The response to a prolonged period of stimulation (3 Hz for 5 min) was evenly depressed by FK 888 or GR 82,334, while GR 94,800 was more effective in inhibiting the late (87% inhibition) than the peak response (25% inhibition). In the presence of nifedipine (1 microM) a marked inhibition of the nonadrenergic noncholinergic contraction was observed and a time lag was evident between stimulus application and onset of contraction, which showed slow onset and offset kinetics. The nifedipine-resistant nonadrenergic noncholinergic contraction was unaffected by FK 888 or GR 82,334 but was suppressed by GR 94,800. Submaximally effective (1-3 nM) concentrations of substance P and neurokinin A produced distinct patterns of contraction: the response to substance P was fast and declined rapidly toward baseline; the response to neurokinin A was slow and sustained. In the presence of nifedipine, the response to substance P was greatly depressed and became slower in onset; nifedipine did not affect the contraction to neurokinin A but slowed its time-course. In sucrose gap experiments, either a short (10 Hz for 1 s) or a prolonged period of electrical stimulation (3 Hz for 3 min) evoked membrane depolarization, action potentials and contraction: in response to the "prolonged" stimulation, distinct phasic and tonic component of contraction were observed. Nifedipine abolished action potentials and the phasic contraction produced by a short period of stimulation, reduced by about 50% the maximal contraction developed during the prolonged stimulation without affecting the amplitude of the tonic response. In the presence of nifedipine, GR 82,334 (3 microM) blocked the membrane depolarization but did not affect contraction; GR 94,800 (0.1 microM) did not affect depolarization but abolished contraction.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition by SR 140333 of NK1 tachykinin receptor-evoked, nitric oxide-dependent vasodilatation in the hamster cheek pouch microvasculature in vivo

1. This study investigated tachykinin-evoked vasodilatation in the microvasculature of the hamster cheek pouch in vivo. Arterioles and venules were observed by intravital microscopy with video recording, and vasodilatation and constriction, defined as changes in blood vessel diameter, measured by image analysis. All agents were applied topically by superfusion. None of the agents tested had a significant effect on venule diameter. 2. When arterioles were preconstricted (by ca. 50%) with endothelin-1 present in the superfusing medium, substance P (0.3-30 nM) was a potent vasodilator, being 10 fold more active than both neurokinin A and the NK1 receptor-selective agonist, substance P methyl ester. The NK2 receptor-selective agonist, [beta-Ala8]-NKA(4-10)(0.1-10 microM) was active only at high concentrations, and the NK3 receptor-selective agonist senktide (0.1-10 microM) was virtually inactive (n = 8 hamsters). Dilatation evoked by tachykinins and analogues was rapid in onset (< 0.5 min) and readily reversible. 3. At low concentrations (1-10 nM), the non-peptide tachykinin NK1 receptor antagonist SR140333 ((S)1-(2-[3(3,4-dichlorophenyl)-1-(3-iso-propoxyphenylacetyl)pi peridin-3- yl]ethyl)-4-phenyl-1-azoniabicyclo[2.2.2]octone, chloride) had no effect on the diameter of preconstricted arterioles per se, but potently inhibited dilator responses to substance P methyl ester (apparent pKB 9.9 +/- 0.2; n = 5 hamsters, n = 10 estimates). SR140333 (10 nM) did not inhibit submaximal dilator responses evoked by human alpha calcitonin gene-related peptide (alpha CGRPh; 1.0 nM; P > 0.05; n = 5). 4 The nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 10 microM) caused a51.3 +/- 5.4% arteriolar constriction. In the presence of L-NAME, submaximal vasodilator responses to substance P (10-I00 nM) and carbachol (0.1-1.0 microM) were significantly attenuated (n = 5 hamsters;P<0.05) as compared to responses obtained in preparations that were preconstricted to a similar extent by endothelin-l (48.0 +/- 5.6%). L-NAME (10 M) was without effect on submaximal vasodilator responses to alpha CGRPh (0.1 nM) or sodium nitroprusside (1O nM) (n = 5 hamsters; P> 0.05).5 We conclude that tachykinin-evoked arteriolar vasodilatation in the hamster cheek pouch is mediated via NK, receptor activation and depends, at least in part, on the release of nitric oxide. The NKI receptors mediating vasodilatation can be blocked by topical application of SR140333; which may therefore be useful in the investigation of the role of NK1 receptors in neurogenic inflammation in the microvasculature.

Characterisation of [125I][MePhe7]neurokinin B binding to tachykinin NK3 receptors: evidence for interspecies variance

Human tachykinin NK3 receptors expressed in Chinese hamster ovary (CHO-K1) cells were characterised using the novel radioligand [125I]iodohistidyl,[MePhe7]neurokinin B ([125I][MePhe7]neurokinin B). [125I][MePhe7]neurokinin B was shown to label human NK3 binding sites with high affinity in a saturable and reversible manner. The rank order of affinity of a range of tachykinin ligands confirmed that the tachykinin receptor expressed was the NK3 receptor type. An interspecies comparison of NK3 binding sites revealed pharmacological differences between human, guinea pig and rat tachykinin NK3 receptors. The NK2 selective antagonist SR 48968, inhibited binding of [125I][MePhe7]neurokinin B to NK3 binding sites with Ki values of 287 nM and 205 nM in human and guinea pig respectively, but was > 30-fold less active in the rat.

Characterization of tachykinin mediated increases in [Ca2+]i in Chinese hamster ovary cells expressing human tachykinin NK3 receptors

The nature of the senktide response of the human NK3 receptor expressed in Chinese hamster ovary cells was characterised using the Ca2+ sensitive dye Fura-2 and imaging methods. Application of the NK3 receptor agonist senktide caused an increase in [Ca2+]i in the cells. The profile for NK3 receptor agonists was that senktide was more potent than [beta-Ala8]neurokinin A-(4-10) which was more potent than [Sar9,Met(O2)11]substance P. SR 48968 was a poor antagonist of the senktide response in intact cells confirming the weak affinity of this agent for the NK3 receptor (IC50 of approximately 1 microM) shown in binding assays. The NK3 receptor mediated increase in intracellular Ca2+ was independent of [Ca2+]o, blocked by the microsomal Ca2+ ATPase inhibitor thapsigargin and the phospholipase C inhibitor U73122 but not by ryanodine. Thus the source of the Ca2+ was probably a ryanodine insensitive, inositol triphosphate sensitive intracellular store.

Differential ability of tachykinin NK-1 and NK-2 agonists to produce scratching and grooming behaviours in mice

Potent and selective NK-1 and NK-2 agonists as well as compounds with lower selectivity and affinity for NK-1 binding sites were compared in their ability to produce scratching and grooming behaviours when injected intracerebroventricularly in mice. Septide, an agonist with a low affinity for NK-1 binding sites, [Sar9, Met(O2)11]SP and to a lesser extent [Pro9]SP, two potent and selective NK-1 agonists were the most effective drugs in stimulating these behaviours. Only high doses of [Apa9,10]SP and [Lys5, Tyr7, Pro8]NKA(4-10), two agonists with low affinity for NK-1 binding sites, produced scratching and grooming responses. Similarly, only high doses of [Lys5, MeLeu9, NLe10]NKA(4-10), a potent NK-2 agonist, produced grooming behaviour. When coinjected with the endopeptidase enzyme inhibitor phosphoramidon, the effects of [Apa9,10]SP, [Lys5, Tyr7, Pro8]NKA(4-10) and [Pro9]SP were markedly enhanced. Analyses of the potency of the different agents to displace 3H-SP binding in mouse subcortical structures revealed that the affinities of the agonists for NK-1 receptors are similar to those previously reported in rat brain. The efficacy of the agonists at producing behavioural responses was not equivalent to their potency to bind to central NK-1 receptors. These findings therefore suggest that a stimulation of NK-1 but also non classical NK-1 receptors are involved in the induction of scratching and grooming behaviours.

Blockade by oral or parenteral RPR 100893 (a non-peptide NK1 receptor antagonist) of neurogenic plasma protein extravasation within guinea-pig dura mater and conjunctiva

1. The ability of an NK1 receptor antagonist, RPR 100893, and its enantiomer, RPR 103253 to block neurogenic plasma protein extravasation in guinea-pig dura mater and conjunctiva was assessed following 125I-labelled bovine serum albumin ([125I]-BSA, 50 muCi kg-1, i.v.) and unilateral electrical stimulation of the trigeminal ganglion (0.6 mA, 5 ms, 5 Hz, 5 min) or capsaicin administration (150 micrograms kg-1, i.v.). 2. When administered p.o. 60 min prior to electrical stimulation, RPR 100893 (> or = 0.1 microgram kg-1) decreased plasma protein extravasation in dura mater in a dose-dependent manner, whereas the enantiomer (10 or 100 micrograms kg-1, p.o.) was inactive. 3. When given i.v. 30 min prior to electrical stimulation, RPR 100893 (> or = 0.5 ng kg-1) significantly inhibited plasma protein extravasation in the dura mater evoked by electrical stimulation in a dose-dependent manner. 4. RPR 100893 (100 micrograms kg-1, p.o.) also reduced the leakage when given 45 min before the guinea-pigs were killed and 10, 40 and 80 min after electrical trigeminal stimulation. 5. RPR 100893 given p.o. dose-dependently inhibited capsaicin-induced plasma protein extravasation with ID50S of 7.4 micrograms kg-1 and 82 micrograms kg-1 for dura mater and conjunctiva, respectively. 6. These results are consistent with the contention that NK1 receptors mediate neurogenic plasma protein leakage following trigeminal stimulation, and suggest that NK1 receptor antagonists of the perhydroisoindolone series may be useful for treating migraine and cluster headaches.

Presence of NK3-sensitive neurones in different proportions in the medial habenula of guinea-pig, rat and gerbil

Electrophysiological recordings were made from neurones of the medial habenula (Mhb) in brain slices obtained from guinea-pig, rat and gerbil brain. The selective NK3 agonist, senktide, was used to determine the relative number of NK3-sensitive-neurones in the Mhb of each species. The proportion of neurones responding to NK1 (Sar9Met(O2)11SP) and NK2 (beta Ala8NKA(4-10) agonists was also assessed. All (65/65) of the guinea-pig Mhb neurones tested were excited by the NK3 agonist, but NK1 and NK2 agonists were without effect. NK3 responses in the guinea-pig were not altered by the presence of a selective NK1 antagonist, CP-99,994. NK1, NK2 and NK3 agonists were without effect on Mhb neurones from gerbil brain slices. In agreement with findings from previous studies, a population of rat Mhb neurones responded to NK1 or NK3 agonists alone or were excited by both. These data show that there is a difference in both the number of NK-sensitive neurones and the type of NK response found in the medial habenula of the three species. The high sensitivity to an NK3 agonist, combined with the apparent lack of NK1 and NK2 responses in the guinea-pig Mhb makes this preparation ideal for studies of central NK3-mediated events.

Localization of striatal and nigral tachykinin receptors in the rat

The effects of lesioning mesostriatal dopamine projections or striatal neurons on tachykinin binding in the basal ganglia were assessed in the rat. 6-Hydroxydopamine lesions of the medial forebrain bundle destroyed striatal dopamine terminals as assessed by [3H]mazindol autoradiography, but did not significantly affect the binding of NK-1 ([3H][Sar9,Met(O2)11]substance P) or NK-3 ([3H]senktide) tachykinin ligands in the striatum. 6-Hydroxydopamine lesions significantly reduced NK-3 binding in the substantia nigra pars compacta, but not the ventral tegmental area. In contrast, striatal quinolinic acid lesions reduced both NK-1 and NK-3 binding in the striatum, but failed to affect NK-3 binding in the substantia nigra. These findings suggest that both NK-1 and NK-3 receptors within the striatum are predominantly post-synaptic with respect to dopamine neurons, whereas nigral NK-3 receptors are located on dopaminergic neurons.

Cardiovascular and behavioural effects of centrally administered tachykinins in the rat: characterization of receptors with selective antagonists

1. The effects of intracerebroventricular (i.c.v.) injection of selective and potent NK1 (RP 67580), NK2 (SR 48968) and NK3 (R 486, [Trp7, beta-Ala8]NKA(4-10)) receptor antagonists were assessed on the cardiovascular and behavioural responses elicited by the i.c.v. injection of substance P (SP), neurokinin A (NKA) or [MePhe7]neurokinin B ([MePhe7]NKB) in the conscious freely moving rat. 2. SP, NKA and [MePhe7]NKB (5-650 pmol) evoked dose-dependent increases in mean arterial blood pressure (MAP) and heart rate (HR) with the rank order of potency SP > NKA > [MePhe7]NKB. The cardiovascular responses were accompanied by excessive face washing, grooming and wet dog shakes. 3. The cardiovascular effects and face washing behaviour induced by SP (25 pmol) were significantly reduced by the pre-injection (i.c.v., 5 min earlier) of RP 67580 (6.5 nmol). However, this antagonist failed to affect the central effects of 25 pmol NKA or [MePhe7]NKB. 4. The cardiovascular and behavioural responses (except for wet dog shakes) elicited by NKA (25 pmol) were significantly reduced by 6.5 nmol SR 48968. However, the latter antagonist had no effect on the SP or [MePhe7]NKB-mediated responses. 5. Both cardiovascular and behavioural effects produced by either SP or NKA (25 pmol) were completely abolished when rats were pretreated with a combination of RP 67580 (6.5 nmol) and SR 48968 (6.5 nmol), yet this combination of antagonists failed to modify the central effects of [MePhe7]NKB. 6. R 486 (6.5 nmol) inhibited the cardiovascular effects as well as wet dog shakes produced by [MePhe7]NKB, but it was inactive against the responses induced by either SP or NKA. 7. None of the tachykinin receptor antagonists or agonists caused motor impairment or respiratory distress. All antagonists blocked in a reversible manner and were devoid of intrinsic activity except R486 (6.5 nmol) which produced a transient increase of MAP and HR.8. These results suggest that the central effects of SP, NKA and [MePhe7]NKB are primarily mediated by central NK1, NK2 and NK3 receptors, respectively. However, a minor activation of NK2 receptors bySP and NK1 receptors by NKA was seen during blockade of both receptors. This study therefore supports the existence of functional NK1, NK2 and NK3 receptors in the adult rat brain.

Cardiovascular and behavioural effects of centrally administered neuropeptide K in the rat: receptor characterization

1. The cardiovascular and behavioural responses to intracerebroventricularly (i.c.v.) administered neuropeptide K (NPK) were studied in conscious rats. The central effects of NPK were characterized by pretreatment (i.c.v.) with selective antagonists for the NK1 ((+/-)-CP 96345 and RP 67580), NK2 (SR 48968) and NK3 (R 487) receptors. 2. NPK (10-65 pmol) induced tachycardia and dose-dependent increases of mean arterial blood pressure. The cardiovascular responses reached a maximum within 3 min post-injection and lasted for more than 1 h. Concurrently, NPK produced dose-dependent increases of face washing, head scratching, grooming, walking and wet dog shakes. 3. A desensitization of most of the behavioural responses (except head scratching) but not of the cardiovascular response was shown when two consecutive injections of 25 pmol NPK were given 24 h apart. 4. Both the cardiovascular and behavioural responses (except the head scratching) to 25 pmol NPK were blocked by pre-administration (i.c.v.) of 6.5 nmol (+/-)-CP 96345 or RP 67580 given 5 min earlier. No inhibition of NPK responses was observed when 6.5 nmol SR 48968 or R 487 were used in a similar study. Additionally, NPK effects were significantly reduced 24 h after the prior injection of (+/-)-CP 96345 but not of RP 67580. 5. These results support the involvement of NK1 receptors in the cardiovascular and behavioural effects of i.c.v. NPK. Thus, this peptide may play a putative role in central cardiovascular regulation as it is the most potent endogenous tachykinin described centrally, to date.

Rational design of high affinity tachykinin NK1 receptor antagonists

The rational design of a non-peptide tachykinin NK1 receptor antagonist, [(2-benzofuran)-CH2OCO]-(R)-alpha-MeTrp-(S)-NHCH(CH3)P h (28, PD 154075) is described. Compound 28 has a Ki = 9 and 0.35 nM for the NK1 receptor binding site in guinea-pig cerebral cortex membranes and human IM9, cells respectively (using [125I] Bolton-Hunter-SP as the radioligand). It is a potent antagonist in vitro where it antagonises the contractions mediated by SPOMe in the guinea-pig ileum (KB = 0.3 nM). Compound 28 is active in vivo in the guinea-pig plasma extravasation model, where it is able to block the SPOMe-induced protein plasma extravasation (monitored by Evans Blue) in the bladder with an ID50 of 0.02 mg kg-1 iv.

Non-peptide angiotensin receptor antagonists bind to tachykinin NK3 receptors of rat and guinea pig brain

[3H]Senktide, a highly selective tachykinin NK3 receptor agonist, was used to study tachykinin NK3 receptors of rat and guinea pig brain. Guinea pig brain membranes had a Kd of 3.9 +/- 0.5 nM and a Bmax of 42 fmol/mg. Dose-displacement experiments with neurokinins and selective tachykinin receptor agonists revealed the following order of potency: [MePhe7]neurokinin B > neurokinin B > substance P > neurokinin A. This order is typical for a tachykinin NK3 receptor. To further characterize the specificity of this receptor, the effects of unrelated compounds such as: bradykinin, angiotensin II, bombesin and their structural analogs were also evaluated on the binding of [3H]senktide. Unexpectedly, the angiotensin AT1 receptor antagonists, DuP 753 (2-n-butyl-4-chloro-5-hydroxymethyl-1-[2'-(1H-tetrazol-5-yl)bip hen yl-4-yl)methyl]imidazole potassium salt), L-158,809 (5,7-dimethyl-2-ethyl-3-[(2'-(1H-tetrazol-5-yl) [1,1'-biphenyl]-4-yl) methyl]-3H-imidazo[4,5-beta]pyridine H2O) and EXP 3174 (2-n-butyl-4-chloro-1-[2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]i midazole- 5-carboxylic acid), inhibited the binding of [3H]senktide to its receptor in the guinea pig brain membranes with IC50 values of 18 microM, 25 microM and 50 microM, respectively. Similar effects were also observed with rat brain membranes. Angiotensin II, saralasin ([Sar1,Val5,Ala8]angiotensin II, a peptide angiotensin AT1 receptor antagonist) and PD 123,319 (1-[4-(dimethylamino)3-methylphenyl]methyl-5-(diphenylacetyl)-4,5, 6,7- tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid, a known non-peptide angiotensin AT2 receptor antagonist) did not inhibit the binding of [3H]senktide to either type of membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigation of the specificity of FK 888 as a tachykinin NK1 receptor antagonist

1. A recently described peptide tachykinin (NK1) receptor antagonist, FK 888, was found to inhibit the electrically-evoked, tachykinin-mediated contractile responses of the rabbit iris sphincter in a concentration-dependent manner; the pIC50 value was 6.6 +/- 0.08. 2. Contractions induced by a selective NK1 receptor agonist, [Sar9,Met(O2)11]substance P, were inhibited competitively by FK 888; the pKB value was 7.1. 3. FK 888 (1 nM-100 microM) was without effect on the electrically-evoked, cholinergic response of the rabbit iris sphincter and the electrically-evoked, sympathetic response of the guinea-pig vas deferens. The contractions of the rabbit iris sphincter, induced by either carbachol (10 nM-30 microM) or noradrenaline (0.1-100 microM), were not affected by 10 microM FK 888. 4. FK 888 (1-30 microM) did not induce histamine release from rat peritoneal mast cells. 5. FK 888 (33 and 333 microM) was without effect on the electrically-evoked action potentials of the frog sciatic nerve. Thus, FK 888 is a moderately high affinity and selective tachykinin (NK1) receptor antagonist.

Interleukin-6 secretion from human astrocytoma cells induced by substance P

Functional NK-1 (substance P) receptors have been demonstrated previously on astrocytes from primary newborn rat brain cultures and human astrocytoma cells lines by specific [125I]-Bolton Hunter substance P (SP) binding and by SP-induced phosphoinositol turnover. In addition, these cells have been shown to release cytokines upon stimulation with interleukin-1 (IL-1) and lipopolysaccharide (LPS). Since SP has also been shown to induce cytokine release from rat glial cells, this neuropeptide may contribute to the pathophysiology of neuronal inflammation in humans by stimulating cytokine production in the brain. We, therefore, explored whether SP could induce U-373 MG human astrocytoma cells, via specific NK-1 receptor activation, to secrete interleukin-6 (IL-6), a cytokine implicated as a key mediator of immune and inflammatory responses. SP stimulated IL-6 production in a concentration-dependent manner with an MC50 (concentration inducing 50% of the maximum response) of 45 nM. IL-6 was detected in the cell culture supernatant fluids 2 h post stimulation and secretion peaked at 12 h. SP induced IL-6 secretion was not mediated by IL-1 since neutralizing anti-IL-1 (alpha and beta) antibody treatment had no effect on the SP response. The selective NK-1 receptor agonist, [Sar9, Met(O2)11]-SP, was comparably effective to SP in stimulating IL-6 secretion; however, selective NK-2 and NK-3 receptor agonists were 250-500-fold less effective. In addition, the non-peptide NK-1 receptor antagonist, (+/-)CP-96,345, inhibited SP (Ki = 4 nM), but not IL-1-induced IL-6 release. These selectivity and specificity studies confirmed the presence of functional NK-1 type receptors linked to IL-6 release. The results of this study support a role for SP as a modulator of immune and/or inflammatory processes in the human CNS.

SR 140333, a novel, selective, and potent nonpeptide antagonist of the NK1 tachykinin receptor: characterization on the U373MG cell line

The effects of a novel nonpeptide NK1 tachykinin receptor antagonist, SR 140333, on the functional consequences of NK1 receptor activation in a human astrocytoma cell line, U373MG, were investigated. Radioligand binding conducted with 125I-Bolton-Hunter substance P revealed a competitive inhibition by SR 140333 and its R enantiomer SR 140603 with Ki values of 0.74 and 7.40 nM, respectively. The NK1-selective agonist, [Sar9,Met(O2)11]-substance P, stimulated the formation of inositol phosphates with an EC50 of 3.8 x 10(-9) M. SR 140333 blocked the stimulatory effect of this agonist (10(-7) M) with an IC50 of 1.6 x 10(-9) M, whereas the effect of another NK1 agonist, septide (EC50 = 1.5 x 10(-8) M) was antagonized with an IC50 of 2.1 x 10(-10) M. Enhancement of [3H]taurine release by [Sar9,Met(O2)11]-substance P (EC50 = 7.4 x 10(-9) M) was also inhibited by SR 140333 with an IC50 of 1.8 x 10(-9) M. SR 140603 was 10-fold less potent than SR 140333 in inhibiting inositol monophosphate formation and [3H]taurine release. The calcium mobilization induced by [Sar9,Met(O2)11]-substance P (10(-8) M) was totally prevented by 10(-8) M SR 140333. Patch-clamp experiments showed that SR 140333 depressed the outward current evoked by 5 x 10(-8) M [Sar9, Met(O2)11]-substance P with an IC50 of 1.3 x 10(-9) M. The expression of c-fos was stimulated by [Sar9,Met(O2)11]substance P with an EC50 of 2.5 x 10(-10) M, an effect that was also inhibited by SR 140333 with an IC50 of 1.1 x 10(-9) M.(ABSTRACT TRUNCATED AT 250 WORDS)

Different Ca2+ influx pathways mediate tachykinin receptor-induced contraction in circular muscle of guinea-pig colon

We used an electrophysiological approach (single sucrose gap) to compare the mechanism of action of selective tachykinin NK1 and NK2 receptor agonists ([Sar9]substance P sulfone and [beta ala8]neurokinin A-(4-10), respectively) in producing contraction of the circular muscle of the guinea-pig proximal colon. [Sar9]Substance P sulfone produced a marked depolarization, action potentials and increase in membrane conductance. On the other hand, [beta Ala8]neurokinin A-(4-10) produced less depolarization of the cell membrane and did not change membrane resistance. Nifedipine (1 microM) greatly reduced (80% inhibition) the contraction due to [Sar9]substance P sulfone while that due to [beta Ala8]neurokinin A-(4-10) was slightly affected (13% inhibition). Action potentials induced by either agonist were suppressed by nifedipine, while depolarization was reduced only to a minor extent. When tested in a Ca(2+)-free medium, the contraction produced by either agonist was greatly reduced (84-89%) as compared to the control. In organ bath experiments [Sar9]substance P sulfone and [beta Ala8]neurokinin A-(4-10) produced concentration-dependent contraction of the circular muscle of the colon (EC50 8 and 12 nM, respectively). Nifedipine (1 microM) markedly suppressed the response to [Sar9]substance P sulfone while that to [beta Ala8]neurokinin A-(4-10) was only slightly depressed. These findings demonstrate that NK1 receptor-mediated contraction is strictly linked to membrane depolarization and action potentials generation through nifedipine-sensitive Ca2+ channels (electromechanical coupling) while the NK2 receptor-mediated contraction is substantially unrelated to depolarization and, while being largely dependent upon extracellular Ca2+, is nifedipine-resistant, possibly linked to the opening of non-selective (Ca(2+)-permeable) receptor-gated cation channels (pharmacomechanical coupling).

Comparison of tachykinin NK1 receptors in human IM9 and U373 MG cells, using antagonist (FK888, (+/-)-CP-96,345, and RP 67580) binding

We have used one peptide (FK888) and two non-peptide ((+/-)-CP-96,345 and RP 67580) antagonists, along with the preferred endogenous agonist, substance P, to compare the pharmacological (binding) profile of NK1 receptors expressed by human B lymphoblastoma (IM9) and astrocytoma (U373 MG) cells. Of the ligands tested, substance P was the most potent in both cell lines: binding affinities were 0.1 nM for IM9 cells, and 0.3 nM for U373 MG cells, respectively. The high-affinity dipeptide antagonist, FK888, bound to NK1 receptors in both cell lines with similar potencies: Ki values were 1.2 nM and 3.6 nM for IM9 cells and U373 MG cells, respectively. Of the non-peptide antagonists, as expected, (+/-)-CP-96,345 displayed higher affinity (0.4 nM in IM9 cells, and 1.2 nM in U373 MG cells) than did RP 67580 (33 nM and 223 nM in IM9 cells and U373 MG cells, respectively) in both cell lines. We conclude that the pharmacological profile of NK1 receptors is similar in the human lymphoblastoma and astrocytoma cells, i.e. if NK1 receptor subtypes exist in humans, these cell lines are likely to express a similar subtype. Because IM9 cells grow faster and are easier to maintain, this cell line may be preferable to the astrocytoma cells as a primary screen to identify NK1 receptor antagonists.

Chromodacryorrhea and repetitive hind paw tapping: models of peripheral and central tachykinin NK1 receptor activation in gerbils

The in vivo pharmacological profiles of the selective tachykinin NK1 receptor agonists, [Sar9,Met(O2)11]substance P and GR 73632, were examined in gerbils. Both agonists induced a pronounced chromodacryorrhea following intravenous injection which was stereoselectively antagonised by the tachykinin NK1 receptor antagonist, CP-99,994, but not by its inactive enantiomer, CP-100,263, or the rat-selective tachykinin NK1 receptor antagonist, RP 67,580. In contrast, chromodacryorrhea was not observed following intravenous injection of the selective tachykinin NK2 receptor agonist, [beta-Ala8]neurokinin A-(4-10), or the selective tachykinin NK3 receptor agonist, senktide. These results suggest that [Sar9,Met(O2)11]substance P-induced chromodacryorrhea results from activation of peripheral tachykinin NK1 receptors. Repetitive hind paw tapping was also observed in gerbils but only following intracerebroventricular injection of [Sar9,Met(O2)11]substance P or GR 73632. Furthermore, GR 73632-induced hind paw tapping was significantly attenuated by co-administration of the peptide tachykinin NK1 receptor antagonist, GR 82334, or intravenous injection of CP-99,994. Thus, in contrast to chromodacryorrhea, repetitive hind paw tapping may result from activation of central tachykinin NK1 receptors.

Characterization of NK1 and NK2 tachykinin receptors in guinea-pig and rat bronchopulmonary and vascular systems

1. NK1 and NK2 tachykinin receptors were characterized in guinea-pig and rat bronchopulmonary systems and in the vasculature of the rat by use of radioligand binding and/or functional studies. 2. The radioligands for NK1 and NK2 receptors ([3H]-SP and [3H]-pNKA, respectively) did not label tachykinin receptors in homogenates of rat lungs or bronchi. In contrast, in the guinea-pig, [3H]-SP bound with high affinity to these tissues (KD = 0.23 +/- 0.08 nM and 0.34 +/- 0.05 nM, for lungs and bronchi, respectively). The total number of binding sites was 4.6 fold greater in bronchus (Bmax = 135 +/- 27 fmol mg-1 protein) than in lung homogenates (Bmax = 29.3 +/- 0.1 fmol mg-1 protein). Furthermore, this binding was markedly displaced by CP-96,345 (pKi = 9.5 +/- 0.1) and RP 67580 (pKi = 7.6 +/- 0.1), antagonists of NK1 receptors, slightly displaced by SR 48968 (pKi = 6.6 +/- 0.1), but not affected by actinomycin D or L-659,877, antagonists of NK2 receptors. Specific binding of [3H]-pNKA, detected in guinea-pig bronchi (KD = 5.2 +/- 0.1 nM, and Bmax = 203 +/- 19 fmol mg-1 protein) but not in lungs, was similarly (40 to 53%) displaced by RP 67580 (1 microM), CP-96,345 (10 and 100 nM) or SR 48968 (10 and 100 nM). The displacement approximately doubled (87 to 91%) when SR 48968 (10 nM) was combined with either RP 67580 (1 microM) or CP-96,345 (10 nM), but not when RP 67580 was combined with CP-96,345. 3. In urethane-anaesthetized guinea-pigs, i.v. injections of the NK1 receptor agonists SP, [Pro9]-SP, [Sar9,Met(O2)11]-SP and septide, as well as the NK2 receptor agonists NKA and [Lys5,MeLeu9,NLeu10]-NKA(4-10) (0.1-10 micrograms kg-1, i.v.), dose-dependently increased lung inflation pressure. The most potent of these peptides were septide and [Lys5, MeLeu9,NLeu10]-NKA(4-10) (EC50 = 0.38 +/- 0.07 and 0.07 +/- 0.02 microgram kg-1, respectively). Interestingly, septide was 130 fold less potent than SP in displacing [3H]-SP from its binding sites in the guinea-pig lung, whereas it was 14 fold more potent than SP as a bronchoconstrictor. RP 67580 (0.3-5 mg kg-1, i.v.) and CP-96,345 (0.01-3 mg kg-1, i.v.) dose-dependently reduced the bronchoconstriction produced by the NK1 receptor agonists. Conversely, the NK2 receptor antagonists actinomycin D (1-10 mg kg-1, i.v.) and SR 48968 (0.03-0.3 mg kg-1, i.v.) inhibited specifically the responses induced by NK2 receptor agonists.4. In pentobarbitone-anaesthetized rats, the NK1 and NK2 receptor agonists (0.01-4 microg kg-1, i.v.)produced dose-dependent hypotensive responses. The order of potency was SP = [Sar9, Met(0211]-SP = [Pro9]-SP > septide = NKA >[Lys5, MeLeu9, NLeu 10-NKA.(4-10). RP 67580 (0.13-0.5 mg kg-1,i.v.) and CP-96,345 (0.5-2 mg kg-1, i.v.) antagonized in a dose-related manner (20 to 64%) the vascular effects of both NK, and NK2 receptor agonists, whereas actinomycin D (3 mg kg-1, i.v.) and SR 48968(2 mg kg-1, i.v.) did not. RP 67580 was approximately 4 times more potent than CP-96,345.5. These studies indicate that NK1 and NK2 receptors are both present in the guinea-pig bronchopulmonary system whereas only NK1 receptors are detectable in the rat vasculature under our experimental conditions. Furthermore, NK1 receptors in the guinea-pig bronchopulmonary system are pharmacologically distinct from those present in the rat vascular system, since both agonist potencies and antagonist affinities differ between the two species.

The vanilloid (capsaicin) receptor: receptor types and species differences

1. Capsaicin was postulated to exert its pharmacological actions by interacting at a specific recognition site (receptor) expressed predominantly by primary afferent neurons. 2. The actual existence of this long-sought "capsaicin-receptor" has recently been demonstrated by the specific binding of [3H]resiniferatoxin (RTX), an ultrapotent capsaicin analog with a unique spectra of actions. 3. Since homovanillic acid is the key structural motif shared by capsaicin and RTX, their recognition site appears to be best termed the vanilloid receptor. 4. Central (sensory ganglia and spinal cord) vanilloid receptors of the rat bind RTX with high affinity in a cooperative fashion; moreover, they recognize capsaicin with higher affinity than the competp6ive antagonist, capsazepine. Peripheral (urinary bladder, urethra, airways, colon) vanilloid receptors, by contrast, bind RTX with lower affinity in a noncooperative manner. An opposite affinity for capsazepine relative to capsaicin appears to distinguish vanilloid receptors in the urinary bladder from those present in the airways or colon. These findings imply heterogeneity in the properties of vanilloid receptors. 5. The affinity of [3H]RTX binding in vitro is influenced by reducing agents, suggesting an in vivo modulatory role for endogenous reducing agents in vanilloid receptor functions. 6. The size of central vanilloid receptors (270 kDa) as measured by radiation inactivation and the cooperative binding both suggest a receptor cluster with cooperating subunits. 7. RTX binds to vanilloid receptors with orders of magnitude higher affinity than capsaicin; its ability to induce cooperative binding is also more pronounced. These differences in receptor binding along with the pharmacokinetical differences in tissue equilibration and in plasma binding may form a rational basis to explain the peculiar spectrum of actions of RTX. 8. Guinea pig spinal cord and airway membranes bind RTX with lower affinity than rat tissues. The receptor density is, however, higher in the guinea pig in keeping with the marked sensitivity of this species to vanilloid actions. 9. The apparently low level of specific [3H]RTX binding sites in the hamster and rabbit is in accord with the resistance of these species to vanilloid actions. 10. In post-mortem human spinal cord specific [3H]RTX binding sites can be detected; their binding parameters are similar to those determined in guinea pig spinal cord. 11. The vanilloid receptor appears to display both intraspecies heterogeneity and marked interspecies differences. 12. As yet, it is known whether the vanilloid receptor is operated by endogenous ligands. It is not known either which receptor superfamily (if any) it belongs to. The [3H]RTX binding assay has, however, the potential of answering these questions.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of longitudinal muscle-myenteric plexus removal and indomethacin on the response to tachykinin NK-2 and NK-3 receptor agonists in the circular muscle of the guinea-pig ileum

1. The effect of removal of the longitudinal muscle-myenteric plexus (LM-MP) and/or indomethacin (10 microM) on the response to the tachykinin NK-2 receptor selective agonist, [beta Ala8]NKA(4-10), or to the NK-3 receptor selective agonist, senktide, was investigated by measuring mechanical activity (isotonic recording) of circular muscle (ring preparation) of the guinea-pig ileum. 2. Indomethacin (10 microM) increased the percentage of ileal rings displaying spontaneous activity, either intact or LM-MP-free. The response to senktide (10 nM and 1 microM) was lower in LM-MP-free than in intact ileal rings, either in the absence or presence of indomethacin. The response to a low concentration (10 nM) of [beta Ala8] NKA (4-10) was enhanced in LM-MP-free rings and by indomethacin. 3. In intact ileal rings, the response to senktide was unaffected by atropine (3 microM) alone or by the tachykinin NK-2 receptor antagonist MEN 10,376 (10 microM) alone while it was reduced by the combined administration of the two antagonists. The response to senktide was greatly reduced by tetrodotoxin (TTX, 1 microM). Senktide-induced contractions (10 nM) were also reduced by the blocker of N-type voltage-sensitive calcium channels, omega-contoxin (CTX, 0.1 microM). 4. In about 30% of preparations tested, an inhibitory response (decrease in spontaneous activity) to 10 nM senktide, was disclosed in CTX-treated intact ileal rings. This inhibitory effect was TTX-sensitive. 5. In LM-MP-free ileal rings, the response to senktide was abolished or reduced by atropine and MEN 10,376, alone or in combination, and was also reduced or abolished by TTX and CTX. 6. The response to [beta Ala8]NKA (4-10) was inhibited by MEN 10,376, in both intact and LM-MP-free ileal rings while it was unaffected by atropine, TTX or CTX. 7. These results indicate that indomethacin pretreatment induces a regular background activity for studying the motor response to tachykinins in the circular muscle of the ileum, probably by blocking the formation of relaxant prostanoids. A further increase in sensitivity to direct smooth muscle stimulation (NK-2 receptor agonist) can be obtained by removal of the LM-MP. The response to NK-3 receptor stimulation is diminished but not abolished by removal of the LM-MP, suggesting that NK-3 receptors are located on neuronal bodies of myenteric neurons, but possibly also at other sites (possibly, nerve terminals).(ABSTRACT TRUNCATED AT 400 WORDS)

Involvement of neurokinins in the non-cholinergic response to activation of 5-HT3 and 5-HT4 receptors in guinea-pig ileum

1. The involvement of neurokinins in the non-cholinergically-mediated contractile response induced by stimulation of 5-HT3 and 5-HT4 receptors has been examined in the longitudinal muscle-myenteric plexus preparation of the guinea-pig ileum. 2. The 5-HT3 receptor agonist, 2-methyl-5-hydroxytryptamine (2-methyl-5-HT), showed a lower potency in this preparation than the more selective 5-HT4 receptor agonist 5-methoxytryptamine. The effect of both drugs was markedly reduced by atropine. 3. Substance P (SP) and neurokinin B (NKB) produced biphasic concentration-response curves in the preparation. Neurokinin A (NKA), the NK1 receptor agonist, [Sar9,Met(O2)11]SP and the NK3 receptor agonist, senktide yielded monophasic concentration-response curves. 4. After desensitization of the NK1 receptor with SP or [Sar9,met(O2)11]SP, in the presence of atropine, the contractile response to 2-methyl-5-HT was entirely blocked. Desensitization of NK3 receptors with NKB, also in the presence of atropine, fully suppressed the 5-HT4 receptor-mediated contraction evoked by 5-methoxytryptamine. 5. In preparations prelabelled with [3H]-choline, SP produced a concentration-dependent increase in tritium overflow, an index of [3H]-acetylcholine release, while an inverse relationship was found with NKB. At low neurokinin concentrations, the releasing effect of NKB was much more marked. 6. It is suggested that in the response to 5-HT3 receptor stimulation, there is a role for SP and acetylcholine. NKB appears to be preferentially involved in the release of acetylcholine elicited by stimulation of 5-HT4 receptors.

Calcium influx and protein kinase C alpha activation mediate arachidonic acid mobilization by the human NK-2 receptor expressed in Chinese hamster ovary cells

We have cloned a cDNA encoding the human ileal neurokinin-2 (NK-2) receptor which mediates powerful neurokinin A-stimulated arachidonic acid (AA) and prostaglandin release when expressed in CHO cells. Two major signal transduction events appear to underlie this response. Firstly, AA liberation is critically dependent upon agonist-stimulated influx of extracellular Ca2+ although not release from intracellular stores. Secondly, NK-2 receptor-linked AA mobilization requires concomitant PKC activation and based upon limited subtype immunodetectability as well as toxin, identical pretreatment inhibits AA release partially and blocks PKC alpha translocation completely. These observations indicate that in this cell system AA liberation reflects NK-2 receptor-dependent activation of two distinct but converging signal transduction pathways regulated by different G-protein species and involving Ca2+ influx and PKC alpha activation.

Antagonism of substance P and related peptides by RP 67580 and CP-96,345, at tachykinin NK1 receptor sites, in the rat urinary bladder

Tonic contraction of rat urinary bladder was elicited in vitro and in vivo by substance P, two selective NK1 receptor agonists, septide ([pGlu6,Pro9]substance P-(6-11)) and [Sar9,Met(O2)11]substance P, and an NK2 agonist, [Lys5,MeLeu9,Nle10]neurokinin A-(4-10), but not by senktide (succinyl[Asp6,MePhe8]substance P-(6-11)), an NK3 agonist. Substance P only stimulated the NK1 receptors of smooth muscle. The non-peptide selective NK1 receptor antagonists, RP 67580 and CP-96,345, both inhibited substance P-induced contraction (pKB values 6.7 and 5.7; ED50 = 1.4 and 5.0 mg/kg i.v., respectively) and septide-induced contraction (pKB values 7.5 and 6.5; ED50 = 0.076 and 0.250 mg/kg i.v., respectively). Both antagonists, at lower doses, also inhibited substance P- and septide-induced plasma extravasation. That both antagonists blocked the effects of septide much more than the effects of substance P suggests the existence of an NK1 receptor subtype or isoform. Selective NK1 receptor antagonists, by blocking both spasm and plasma extravasation in the urinary bladder, would be useful for treating substance P-related motor disorders and cystitis.

Differential effects of selective tachykinin NK2 receptor antagonists in rat spinal cord

The effects of intrathecally (i.t.) injected selective tachykinin NK2 receptor antagonists, MEN 10,207, MEN 10,376 and R396, on the spinal effect of neurokinin A were studied in decerebrate, spinalized, unanesthetized rats. I.t. neurokinin A (7 pmol) briefly facilitated the flexor reflex, an effect that was dose dependently inhibited by pretreatment with MEN 10,207 and MEN 10,376 with similar and high potency. I.t. R396 itself caused strong facilitation of the flexor reflect. At lower doses, the effect of i.t. neurokinin A was potentiated by R396. R396 only exhibited moderate antagonism of neurokinin A-induced reflex facilitation even at very high doses. It has been proposed that the tachykinin NK2 receptor may be further classified into two subtypes, NK2A and NK2B, with MEN 10,207 and MEN 10,376 having high affinity for the former and R396 for the latter. Our results suggested that the tachykinin NK2 receptor in rat spinal cord which mediates the excitatory effect of neurokinin A may belong to the NK2A subpopulation of receptors.

Conformational study of cyclo[Gln-Trp-Phe-Gly-Leu-Met] as NK-2 antagonist by NMR and molecular dynamics

Cyclo[Gln-Trp-Phe-Gly-Leu-Met] (1) is a selective peptide antagonist of NK-2 receptors. The conformational analysis of this peptide was conducted using nuclear magnetic resonance (NMR) and molecular dynamics. This study improves understanding of the neurokinin ligand-receptor interactions. Two-dimensional Homonuclear Hartmann-Hahn (2D-HOHAHA) and rotating frame Overhauser enhancement spectroscopy (2D-ROESY) were used to assign all the protons and to obtain through-space proton-proton interactions. ROE (rotating frame Overhauser enhancement) constraints molecular dynamics were done to find the conformation which is consistent with the NMR data. Two beta I (or beta V') turns around Trp-2-Phe-3 and around Leu-5-Met-6 are found in this peptide which are represented by models. The conformation of this peptide is also compared with the non-peptide NK-2 antagonist SR-48968 (2).

Neurokinin receptor subtypes characterized by biological assays

Neurokinin receptors have been characterized by biological assays using naturally occurring and selective agonists as well as peptide and non peptide antagonists. Six preparations have been used: the rabbit vena cava and the rat urinary bladder, treated with a NK-2 receptor antagonist for the NK-1 receptor, the rabbit pulmonary artery and the hamster urinary bladder for the NK-2, the rat portal vein and the guinea pig ileum, treated with a NK-1 receptor antagonist, for the NK-3. Treatment with antagonists was required because of the presence (in some preparations) of two functional sites contributing to the biological effect. Differences in the order of potency of agonists between each couple of receptors have been demonstrated, especially with tachykinins and the selective agonists. Such differences are even more evident with antagonists, some of which show apparent affinity (pA2) values 1.5 to 3 log units higher in one than in the other member of each couple. Based on data obtained in pharmacological experiments, it is concluded that NK-1, NK-2 and NK-3 receptors show differences strong enough to justify the assumption that their coding and/or expression diverge among species.

Non-specific actions of the non-peptide tachykinin receptor antagonists, CP-96,345, RP 67580 and SR 48968, on neurotransmission

1. Three non-peptide tachykinin receptor antagonists, CP-96,345, RP 67580 and SR 48968, were found to inhibit the electrically-evoked, tachykinin-mediated contractile responses of the rabbit iris sphincter in a concentration-dependent fashion; the pIC50 values were 5.6 +/- 0.01, 5.4 +/- 0.07 and 4.8 +/- 0.03, respectively. 2. These antagonists also inhibited the electrically-evoked, parasympathetic response of the rabbit iris sphincter and the sympathetic response of the guinea-pig vas deferens in a concentration-dependent manner; the pIC50 values were 0.3-1.2 log units lower than those recorded for the tachykinin-mediated responses. 3. Two local anaesthetics, bupivacaine and oxybuprocaine, were also found to inhibit the tachykinin-mediated, cholinergic and sympathetic contractile responses in these tissues in a concentration-dependent manner; the concentration ranges for producing the inhibition were similar to those of the non-peptide tachykinin receptor antagonists. 4. On the sciatic nerves of frogs, the tachykinin receptor antagonists inhibited action potentials in a concentration-dependent manner; the potency of the three drugs was similar to that of bupivacaine. 5. Our results suggest that, in addition to blocking tachykinin receptors, the non-peptide tachykinin receptor antagonists, CP-96,345, RP 67580 and SR 48968, may exert non-specific inhibitory effects on neurotransmission.

Effects of ageing on tachykinin function in the basal ganglia

The effects of ageing on tachykinin-induced behaviours and tachykinin receptors were investigated in the rat. Infusion of the NK-3 tachykinin agonist senktide (0.25, 0.5 and 1 nmol) into the substantia nigra induced locomotion in young (4-6 months) animals but this response was attenuated in middle-aged (12 months) and old (27 months) animals. In contrast, senktide-induced wet dog shakes were not significantly affected by age. In the ventral tegmental area, senktide induced locomotion and wet dog shakes with bell-shaped dose-response curves which were unaffected by age. Senktide suppressed grooming but the effect reached significance in the older animals only. Quantitative receptor autoradiography revealed no effect of age on NK-1 tachykinin receptor density in the striatum while NK-3 receptor density declined in the ventrolateral striatum and to a nonsignificant degree in the substantia nigra but not in other striatal subregions or the ventral tegmental area. We conclude that ageing of the nervous system is not associated with widespread changes in tachykinin binding but differences in behavioural response to tachykinin agonists may reflect changes in other transmitter systems which respond to tachykinin input.

Involvement of NK1 receptors in synaptic transmission in the guinea pig coeliac ganglion

Using intracellular recording techniques, we examined the effects of tachykinin receptor agonists and antagonists on electrophysiologically identified tonic neurons of the isolated guinea pig coeliac ganglion. In most of the tonic neurons, substance P (SP), neurokinin A (NKA) and/or senktide induced a depolarization. The effects of SP and NKA were blocked by the NK1-selective antagonist, GR71251 (5 microM), but not by the NK2-selective antagonist, L659,877 (10 microM), whereas the effect of senktide was not affected by these antagonists. The NK1-selective agonists, [Sar9,Met(O)2(11)]SP and SP methyl ester, and the NK3-selective agonist, [MePhe7]neurokinin B, also evoked depolarizations in tonic neurons. By contrast, the NK2-selective agonists, [Nle10]NKA4-10, [beta-Ala8]NKA4-10 and GR64349, at 1 microM each, did not evoke any significant depolarizing response. Repetitive electrical stimulation of the mesenteric nerves induced slow excitatory postsynaptic potentials (EPSPs) in the majority of tonic neurons, which were depressed by GR71251 (5 microM). These results suggest that NK1 and NK3 receptors but not NK2 receptors are involved in the tachykinin-induced depolarization of tonic neurons, and that the NKA-induced response is due to the activation of NK1 receptors. This study also suggests the involvement of NK1 receptors in the slow EPSPs in tonic neurons.

Postnatal development of functional dopamine, opioid and tachykinin receptors that regulate acetylcholine release from rat neostriatal slices. Effect of 6-hydroxydopamine lesion

In the present work we have studied the postnatal development of functional dopamine, opioid and tachykinin receptors, which regulate cholinergic activity in the neostriatum. The release of endogenous acetylcholine from rat striatal slices was measured using a chemiluminescent method. We have observed that the inhibition mediated by dopamine through D2 receptors was not detectable until postnatal day 10, whereas the inhibition mediated by opioid receptors was detectable at postnatal day 15 for delta-receptors ([D-Pen2,D-Pen5]-enkephalin) and at postnatal day 21 for mu-receptors ([D-Ala2,Gly(ol)5]-enkephalin). Excitatory effect mediated by tachykinins through NK1 ([Sar9,Met(O2)11]- Substance P), NK2 ([Nle10]-Neurokinin A4-10), or NK3 (senktide) receptors was already detectable at postnatal day 5. In order to examine the influence of dopamine in the development of tachykinin and opioid systems in the neostriatum, we induced dopamine deficiency by intraventricular injection of 6-hydroxydopamine at postnatal day 3. We observed an increase in senktide-evoked acetylcholine release at postnatal day 30. The effect produced by [Sar9,Met(O2)11]-Substance P and [Nle10]-Neurokinin A4-10 was not modified. Furthermore, at postnatal day 35, we could observed that the two opioid receptor agonists have no effect. Our results show that dopamine, tachykinins and opioids are already able to mediate the modulation of acetylcholine release in early stages of development with a different pattern of postnatal development. Furthermore, the integrity of a dopaminergic system plays an important role in the functional development of the neostriatal cholinergic neurons which are differentially modulated by opioids or tachykinins.

Spinal cord amino acid release and content in an arthritis model: the effects of pretreatment with non-NMDA, NMDA, and NK1 receptor antagonists

An experimental arthritis, induced by injection of the knee joint with kaolin and carrageenan, results in guarding of and decreased weight bearing on the limb. At the time of injection, a transient increased release of all amino acids examined is measurable in samples collected by microdialysis. A second and prolonged increase of aspartate (ASP), glutamate (GLU), and glutamine (GLN) concentrations follows after 3 h. The increased release at time of injection is blocked by microdialysis application of a non-N-methyl-D-aspartate (non-NMDA) or an NMDA receptor antagonist, and the release of ASP, GLU, and GLN in the late phase is blocked by pretreatment with a non-NMDA (CNQX), an NMDA (AP7) or a neurokinin 1 (NK1; CP-96,345) antagonist. Dorsal horn immunoreactive staining of GLU, substance P (SP), and calcitonin gene-related peptide (CGRP) is reflective of the events occurring in the late phase of amino acid release since GLU release is positively correlated with GLU staining density. Increased immunoreactivity for GLU, SP, and CGRP at 8 hr in the arthritic animals is differentially altered by pretreatment of the spinal cord dorsal horn with non-NMDA, NMDA, or NK1 receptor antagonists. The differential staining pattern for GLU, SP, and CGRP, the differential release of ASP and GLU, and the differential activation of the EAA and NK1 receptors implies that ASP, GLU, SP, and CGRP are each involved in the processing of sensory information and that their roles in the central sensitization occurring with the inflammatory process, are unique.

Substance P-evoked calcium mobilization and ionic current activation in the human astrocytoma cell line U 373 MG: pharmacological characterization

In the human astrocytoma cell line U 373 MG, application of substance P (SP) leads to a transient increase in cytosolic calcium concentration and to a biphasic current response in voltage-clamped cells. Using these two functional assays we have characterized pharmacologically the SP response in U 373 MG cells. SP and [L-Pro9]SP displayed high potencies in both assays with EC50 values of 2.5 x 10(-9) M and 1 x 10(-9) M on calcium responses and 1 x 10(-9) M and 5 x 10(-9) M on ion current responses, respectively. The high potency of SP and [L-Pro9]SP as well as the low potency of [Lys5,MeLeu9,N-Leu10]neurokinin A(4-10) and the inactivity of senktide demonstrate the NK1-type pharmacology of these responses. Furthermore, the NK1 antagonists (+/-)-CP 96,345, its chloro analogue, (+/-)-cis-3-(2-chlorobenzylamino)-2-benzhydrylquinuclidine, and RP 67580 were potent antagonists of both SP responses. For the calcium mobilization induced by SP (10(-7) M), the IC50 values for the three antagonists were 4 x 10(-10) M, 4 x 10(-9) M, and 9 x 10(-9) M, respectively, whereas on the current response evoked by SP (10(-8) M), the IC50 values were 8 x 10(-9) M, 2.4 x 10(-8) M, and 1.2 x 10(-7) M, respectively. Despite differences in the absolute IC50 values obtained with both techniques, the relative potencies of the three antagonists correlate fairly well.(ABSTRACT TRUNCATED AT 250 WORDS)

NK1 receptors mediate tachykinin-induced plasma extravasation in the rat knee joint

The tachykinin receptor type that mediates tachykinin-induced plasma extravasation in the rat knee joint was identified by using selective antagonists as well as natural or synthetic agonists. Substance P (SP) and neurokinin (NK) A induced plasma extravasation with almost the same potency and the maximum response was obtained at 5 nmol/knee. NKB was about ten times less potent than SP or NKA. The NK1 selective agonist, [Sar9, Met(O2)11]-SP, was about ten times more potent than SP, and the NK2 selective agonist, [Nle10]-NKA4-10, was about fifty times less potent than NK1 agonist. The NK3 agonist, Senktide, was totally ineffective at 0.5-50 nmol/knee. All responses induced by SP (5 nmol/knee), NKA (5 nmol/knee), NKB (50 nmol/knee), NK1 agonist (0.5 nmol/knee) or NK2 agonist (25 nmol/knee) were significantly and profoundly inhibited by the NK1 selective antagonist, RP67580, but not by the NK2 selective antagonist, SR48968. Taken together, we conclude that tachykinin-induced plasma extravasation in the rat knee joint is mediated via NK1 receptors.

Intranigral stimulation of oral movements by [Pro9] substance P, a neurokinin-1 receptor agonist, is enhanced in chronically neuroleptic-treated rats

Bilateral intranigral infusions of three different peptide agonists were made in rats exposed to fluphenazine decanoate, 30 mg/kg/month (FLU) or vehicle (CON) for seven months. Oral movements were monitored repeatedly during the neuroleptic pretreatment period, as well as before the intranigral infusion and during a 90-min period postinfusion. The FLU group had an increased frequency of vacuous chewing movements (VCM) during the pretreatment period in comparison to controls. Intranigral infusion of the neurokinin-1 (NK1) receptor agonist, [Pro9]Substance P (2.5 nmol on each side), 5-7 weeks after the last FLU injection, caused a significant increase of VCM in both pretreatment groups, lasting 7 min after the infusion. The VCM response to [Pro9]Substance P in the FLU group was significantly higher than in the CON group. A NK2 agonist [Lys5, MeLeu9, Nle10]Neurokinin A(4-10) (2.5 nmol) failed to produce significant changes in oral activity. A Leu-enkephalin analogue [D-Ala2,D-Leu5]enkephalin (3.8 nmol) induced a massive biting behavior in both FLU and CON rats. Using VCM as a behavioral assay, an increased nigral sensitivity to a NK1 agonist is demonstrated in rats chronically exposed to neuroleptics. No corresponding alterations could be ascribed for the NK2 receptor agonist or the Leu-enkephalin analogue.