Neurokinin B- and specific tachykinin NK(3) receptor agonists-induced airway hyperresponsiveness in the guinea-pig

1. The aim of this study was to determine whether neurokinin B (NKB) or specific agonists of tachykinin NK(3) receptors, [MePhe(7)]NKB and senktide, were able to induce airway hyperresponsiveness in guinea-pigs. The effects of these compounds were compared to those of substance P (SP), neurokinin A (NKA) and the preferential tachykinin NK(1) ([Sar(9), Met(0(2))(11)]SP) or NK(2) ([betaAla(8)]NKA (4-10)) receptor agonists. 2. In guinea-pigs pretreated with phosphoramidon (10(-4) M aerosol for 10 min) and salbutamol (8.7x10(-3) M for 10 min), all tachykinins administrated by aerosol (3x10(-7) to 10(-4) M) induced airway hyperresponsiveness 24 h later, displayed by an exaggerated response to the bronchoconstrictor effect of acetylcholine (i.v.). The rank order of potency was: [betaAla(8)]NKA (4-10)>NKA=NKB=senktide=[MePhe(7)]NKB=[Sar(9),Met(0(2))(11)]SP>SP. 3. Airway hyperresponsiveness induced by [MePhe(7)]NKB was prevented by the tachykinin NK(3) (SR 142801) and NK(2) (SR 48968) receptor antagonists. 4. Bronchoconstriction induced by tachykinins administered by aerosol was also determined. SP, NKA, NKB and the tachykinin NK(1) and NK(2) receptor agonist induced bronchoconstriction. The rank order of potency was: NKA=[betaAla(8)]NKA (4-10)>NKB=SP=[Sar(9), Met(0(2))(11)]SP. Under similar conditions, and for concentrations which induce airway hyperresponsiveness, senktide and [MePhe(7)]NKB failed to induce bronchoconstriction. 5. It is concluded that tachykinin NK(3)-receptor stimulation can induce airway hyperresponsiveness and that this effect is not related to the ability of tachykinins to induce bronchoconstriction.     

Tachykinin Receptors Mediating Contractions Of Oestrogen-Primed Rat Uterus: Classification Using Non-Peptide Antagonists

1. The aim of the present study was to characterize the tachykinin receptors mediating contractions of the uterus from the oestrogen-primed rat. Apparent pKB values versus mammalian tachykinins and some subtype-selective agonists were determined for the non-peptide NK1, NK2 and NK3 receptor antagonists SR 140333, SR 48968 and SR 142801, respectively. 2. Apparent pKB values for SR 48968 tested at concentrations of 3, 10 and 30 nmol/L versus neurokinin (NKA, [Lys5MeLeu9Nle10] NKA(4-10) and [Nle10] NKA(4-10) were 8.79, 9.44 and 9.33, respectively, indicating activation of an NK2 receptor and, in the case of NKA, the possible activation of an additional receptor subtype. SR 48968 (30 nmol/L) did not affect responses to NKB (1 mumol/L), senktide (30 nmol/L), substance P (SP; 100 nmol/L) or [Sar9Met(O2)11] SP (100 nmol/L), indicating its selectivity at this concentration. 3. SR 140333 (1-100 nmol/L) reduced the effects of the NK1-preferring agonists SP and [Sar9Met(O2)11] SP, indicating the presence of NK1 receptors. The pKB estimate versus [Sar9Met(O2)11] was 9.01. SR 140333 (100 nmol/L) did not affect responses to NK2 and NK3 receptor-preferring agonists. 4. SR 142801 (100 nmol/L to 1 mumol/L) produced small rightward shifts in the log concentration-response curves to NKB, yielding an apparent pKB value of 7.0. At 1 mumol/L, SR 142801 reduced responses to the NK2 agonists, suggesting some non-selectivity at this concentration. 5. Taken together, these data provide strong evidence that tachykinin-induced contractions of the uterus of the oestrogen-primed rat are mediated by NK2 receptors, with some contribution from NK1 receptors.     

Respiratory actions of tachykinins in the nucleus of the solitary tract: characterization of receptors using selective agonists and antagonists

1. The respiratory response to microinjection of tachykinins and analogues into the commissural nucleus of the solitary tract (cNTS) of urethane-anaesthetized rats was investigated in the presence and absence of selective tachykinin NK(1), NK(2) and NK(3) antagonists (RP 67580, SR 48968 and SR 142801, respectively). 2. All tachykinins, except for the selective NK(2) agonist, [Nle(10)]-NKA(4-10), increased tidal volume (VT). The rank potency order of naturally-occurring tachykinins was neurokinin A (NKA)> or =substance P (SP)>NKB, whereas the rank order for selective analogues was senktide> or = septide> [Sar(9),Met(O(2))(11)]-SP>[Nle(10)]-NKA(4-10). Septide (NK(1)-selective) and senktide (NK(3)-selective) were 22 fold more potent (pD(2) approximately 12) at stimulating VT than SP (pD(2) approximately 10.5). 3. Tachykinin agonists produced varying degrees of respiratory slowing, independent of changes in VT. At doses producing maximum stimulation of VT, agonists induced either a mild (<10 breaths min(-1) decrease; SP and septide), moderate (10 - 25 breaths min(-1) decrease; NKA, NKB and [Sar(9),Met(O(2)]-SP) or severe ( approximately 40 breaths min(-1) decrease; senktide) bradypnoea. [Nle(10)]-NKA(4-10) produced a dose-dependent bradypnoea without affecting VT. 4. RP 67580 significantly attenuated the VT response to SP (33 pmol) and NKA (10 pmol) but not NKB (100 pmol). In the presence of RP 67580, the mild bradypnoeic response to NKB was significantly enhanced whereas SP and NKA induced a bradyapnea which was not observed in the absence of RP 67580. SR 48968 had no effect on the VT response to SP or NKB, markedly enhanced the VT response to NKA and completely blocked the bradypnoeic response to [Nle(10)]-NKA(4-10). Only SR142801 attenuated the VT response to NKB. 5. The present data suggest that all three tachykinin receptors (NK(1), NK(2) and NK(3)) are present in the cNTS and are involved in the central control of respiration.     

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.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional characterization of tachykinin NK1 receptors in the mouse uterus

1. Contractility studies were undertaken to determine the nature of the receptors mediating responses to tachykinins in uteri of oestrogen-treated mice. 2. In the presence of thiorphan (3 microM), captopril (10 microM), and bestatin (10 microM), substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) produced concentration-related contractions of uterine preparations. The order of potency was SP > or =NKA>NKB. 3. Neither atropine (0.1 microM) nor l-NOLA (100 microM), nor indomethacin (10 microM) alone or in combination with either ranitidine (10 microM) or mepyramine (10 microM), affected responses to SP. These findings indicate that SP actions are not mediated or modulated through the release of acetylcholine, nitric oxide, prostanoids or histamine. 4. In the presence of peptidase inhibitors, the tachykinin NK(1) receptor-selective agonist [Sar(9)Met(O(2))(11)]SP, produced a concentration-dependent contractile effect. The tachykinin NK(2) and NK(3) receptor-selective agonists [Lys(5)MeLeu(9)Nle(10)]NKA(4-10) and [MePhe(7)]NKB were relatively inactive. The potencies of SP analogues in which Glu replaced Gln(5) and/or Gln(6) were similar to that of SP. 5. The tachykinin NK(1) receptor-selective antagonist, SR140333 (10 nM), alone or combined with the tachykinin NK(2) receptor-selective antagonist, SR48968 (10 nM), shifted log concentration curves to SP, NKA and NKB to the right. SR140333 (10 nM) reduced the effect of [Sar(9)Met(O(2))(11)]SP. SR48968 did not affect responses to SP or [Sar(9)Met(O(2))(11)]SP, but reduced the effect of higher concentrations of NKA and shifted the log concentration-response curve to NKB to the right. The tachykinin NK(3) receptor-selective antagonist, SR 142801 (0.3 microM), had little effect on responses to SP and NKB. 6. We conclude that the tachykinin NK(1) receptor mediates contractile effects of SP, NKA and NKB and [Sar(9)Met(O(2))(11)]SP in myometrium from the oestrogen-primed mouse. The tachykinin NK(2) receptor may also participate in the responses to NKA and NKB.     

Demonstration of a 'septide-sensitive' inflammatory response in rat skin.

1. Measurement of plasma protein extravasation induced by the natural tachykinins following intradermal administration in rat skin indicated equipotency between substance P (SP), neurokinin A (NKA) and neurokinin B (NKB). The selective NK1 receptor agonist, [Sar9]SP sulphone was 10-100 times more potent than SP. The synthetic hexapeptide, septide, [pGlu6, Pro9]SP-(6-11), which has been proposed to act on a distinct NK1 receptor subtype/binding site was equipotent with [Sar9]SP sulphone. 2. The selective NK2 receptor agonist [beta Ala8]NKA(4-10) (0.1-1 nmol) and the selective NK3 receptor agonist, senktide (0.1-1 nmol) were both ineffective in producing oedema. The selective NK2 receptor antagonist, SR 48, 968 (0.3 mumol kg-1) had no significant inhibitory effects upon oedema induced by approximately equiactive doses of SP (0.2 nmol), septide (0.002 nmol), [Sar9]SP sulphone (0.002 nmol), or NKB (0.3 nmol). These results together suggest that neither NK2 nor NK3 receptors are involved in oedema formation in rat skin. 3. The non-peptide tachykinin NK1 receptor antagonist, RP 67,580 (1-3 mumol kg-1), inhibited plasma protein extravasation induced by septide (0.002 nmol) to a greater extent than that to SP (0.2 nmol). RP 67,580 (1 mumol kg-1) produced a significant inhibition of approximately 66% of the response to septide (0.002 nmol) only. Increasing the dose of RP 67,580 3 fold resulted in inhibition of the response to SP (0.2 nmol) and [Sar9]SP sulphone (0.002 nmol) by approximately 66% and 64% respectively with the response to septide being inhibited by approximately 70%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional interaction between losartan and central tachykinin NK3 receptors in the conscious rat.

1. The cardiovascular and behavioural effects elicted by the intracerebroventricular (i.c.v.) injection of substance P (SP), neurokinin A (NKA), [MePhe7]neurokinin B ([MePhe7]NKB) or angiotensin II (AII) in the conscious rat were assessed before and 5 min after i.c.v. pretreatment with antagonists selective for angiotensin AT1 (losartan and its active metabolite EXP 3174), angiotensin AT2 (PD 123,319) or tachykinin NK3 (R 486) receptors. 2. I.c.v. administration of 25 pmol AII evoked an increase in mean arterial blood pressure (MAP) and water intake behaviour, accompanied by a transient bradycardia, whereas 25 pmol [MePhe7]NKB caused a transient increase in MAP and heart rate (HR) concurrently with marked wet dog shake behaviour. At the same dose, SP and NKA were more potent than [MePhe7]NKB in increasing MAP and HR, but did not produce water intake or wet dog shake behaviours. 3. Losartan (650 pmol, i.c.v.) reduced significantly the cardiovascular and behavioural responses to AII or [MePhe7]NKB, but not to SP or NKA. While 65 pmol losartan was inactive, 260 pmol inhibited selectively the central effects of AII. Whereas EXP 3174 (6.5 nmol) blocked both AII and [MePhe7]NKB-mediated responses, the dose of 650 pmol blocked only the responses to AII. 4. The central responses to AII and [MePhe7]NKB were not affected by PD 123,319 (650 pmol). On the other hand, the [MePhe7]NKB-induced central effects were significnatly reduced by R 486 (650 pmol). The NK3-selective antagonist had no effect against AII. 5. This study provides functional evidence, to support earlier binding data, that losartan (and to some extent its active metabolite EXP 3174) interact with the tachykinin NK3 receptor in rat brain.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of cardiac activity by tachykinins in the rat substantia nigra.

1. The effects of tachykinin NK(1), NK(2) and NK(3) receptor agonists and antagonists were measured on blood pressure (MAP) and heart rate (HR) after bilateral microinjection into the substantia nigra (SN) of awake, unrestrained rats. 2. Increasing doses (25 pmol - 1 nmol) of selective agonists at NK(1) ([Sar(9),Met(O(2))(11)]SP), NK(2) ([beta-Ala(8)]NKA(4 - 10)) and NK(3) (senktide) receptors into the SN produced tachycardia which was selectively and reversibly blocked by the prior injection of tachykinin antagonists at NK(1) (RP67580, 250 pmol), NK(2) (SR48968, 250 pmol) and NK(3) (R-820, 500 pmol) receptor. A rapid fall in MAP followed by a pressor response was seen with 1 nmol of [Sar(9),Met(O(2))(11)]SP. Behavioural activity was elicited by 1 nmol of [Sar(9),Met(O(2)(11)]SP (sniffing > face washing = grooming) and senktide (sniffing > wet dog shake > rearing = locomotion). Tachykinin antagonists had no direct cardiovascular or behavioural effects. 3. The tachycardia produced by 100 pmol of [beta-Ala(8)]NKA(4 - 10) or senktide was abolished by an i.v. treatment with atenolol (beta(1)-adrenoceptor antagonist, 5 mg kg(-1)) while that evoked by [Sar(9),Met(O(2))(11)]SP was reduced. A combination of atenolol (5 mg kg(-1)) and atropine (muscarinic antagonist, 1 mg kg(-1)) blocked the response evoked by [Sar(9),Met(O(2))(11)]SP. 4. These data suggest that the SN is a potential site of modulation of cardiac activity by tachykinins. In addition to the withdrawal of the cardiovagal activity by NK(1) receptor, the three tachykinin receptors appear to increase the sympatho/adrenal drive to the heart. This occurs independently of changes in MAP and behaviour. Hence, this study highlights a new central regulatory mechanism of cardiac autonomic activity.     

Radioligand binding and functional characterisation of tachykinin receptors in chicken small intestine

Tachykinin receptors in chicken intestine were studied using radioligand binding and functional techniques. Mechanisms of tachykinin-induced contraction were also investigated. Binding of [125I]Bolton-Hunter substance P ([125I]BH-SP) to chicken ileal membranes was rapid, saturable, of high affinity and to a single population of binding sites with Kd 0.72 nM and Bmax 0.48 fmol/ wet weight tissue. The rank order of agonists competing for [125I]BH-SP binding sites was [Sar9]SP > [Arg3]SP (natural tachykinin in chickens) > SP > [Pro9]SP > or = NKA > eledoisin > [Sar9,Met(O2)11]SP > [Lys5,MeLeu9,Nle10]-NKA(4-10) > senktide, suggesting similarities to the mammalian NK1 receptor. The NK1 receptor antagonist CP 99994, and NK2 receptor antagonist SR 48968 were weak competitors while spantide, RP 67580, GR 82334, GR 94800 and MEN 11420 were ineffective. The radioligand [125I]NKA showed no specific binding to ileal membranes. The potency order of most tachykinins in contacting isolated ileal longitudinal segments was in good agreement with that obtained from competition binding studies. Contractions to [Arg3]SP, NKA and senktide were greatly reduced by tetrodotoxin, suggesting that neurally-mediated responses were primarily involved. [Arg3]SP and NKA acted mainly by increasing release of acetylcholine, prostaglandins and probably tachykinins. Responses to [Arg3]SP were virtually abolished by nifedipine but were unaffected by NK1 receptor antagonists. Senktide-induced contraction was inhibited by the NK3 receptor antagonist, SR 142801, but was unaffected by atropine or L-NAME. The study provides evidence for a tachykinin receptor with similarities to the NK1 receptor in the chicken small intestine. In addition, senktide may act on a receptor similar to the mammalian NK3 receptor.     

Injection of tachykinins and selective neurokinin receptor ligands into the substantia nigra reticulata increases striatal dopamine and 5-hydroxytryptamine metabolism.

Bilateral injection of endogenous tachykinins (substance P (SP), neurokinin A (NKA)) and selective neurokinin receptor ligands (senktide, [Sar9,Met(O2)11]SP, [MePhe7]NKB) into the substantia nigra reticulata increased striatal dopamine and serotonin metabolism. The increase in dopamine metabolism in the dorsal striatum at a low dose of the substances may be a direct effect on dopamine neurons in the substantia nigra reticulata via NK1 and NK3 receptors. The lack of effect at intermediate doses may be due to inhibitory mechanisms or desensitization. The changes after high doses in the dorsal and ventral striatum may be due to actions on dopaminergic neurons in the substantia nigra as well as in the ventral tegmental area, since there was considerable diffusion from the site of injection. An apparent rapid degradation of injected SP or NKA indicates that N-terminal SP fragments may participate in the SP response. The increased serotonin metabolism that occurs only at a high dose may involve all three neurokinin receptors.     

Neurokinins produce selective venoconstriction via NK-3 receptors in the rat mesenteric vascular bed.

The vasoactive properties of the neurokinins (substance P (SP), neurokinin A (NKA), neurokinin B (NKB)) and some selective analogues were assessed in the arterial and venous mesenteric beds of the rat. Although both sides of the mesenteric vasculature displayed endothelium-dependent relaxation in response to acetylcholine (ACh) or bradykinin (BK) (1 and 10 nmol), SP and the selective NK-1 analogue, [Sar9,Met(O2)11]SP were inactive. Of the three selective neurokinin agonists used, [Sar9,Met(O2)11]SP (NK-1), [beta-Ala8]NKA-(4-10) (NK-2) and [MePhe7]NKB (NK-3), only the latter induced a dose-dependent pressor effect in the venous mesenteric vasculature. Injections of SP and the selective NK-1 and NK-2 analogues at high doses (10 nmol), did not change the perfusion pressure in the mesenteric bed even when the mesenteric vasculature was treated with methylene blue (50 microM) to inhibit the effects of endothelium-derived relaxing factor (EDRF) or with NG-nitro-L-arginine (L-NNA) (20 microM) to inhibit the formation of EDRF or with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate] (CHAPS 20 mM, 30 s) to remove the endothelial layer. In contrast, the vasoconstrictor effects of noradrenaline (NA), angiotensin II (ATII), NKB and [MePhe7]NKB on the venous side of the circulation were enhanced following treatment with L-NNA, methylene blue or CHAPS. The present results suggest that neurokinins act on the rat mesenteric bed by increasing the perfusion pressure of the venous vasculature via activation of NK-3 receptors. Neurokinins are inactive on the arterial mesenteric vasculature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of two novel tachykinin antagonists, FK224 and FK888, on neurogenic airway plasma exudation, bronchoconstriction and systemic hypotension in guinea-pigs in vivo.

1. We compared the effects of two novel tachykinin receptor antagonists, FK888 (selective at the tachykinin NK1 receptor) and FK224 (dual antagonist at NK1 and NK2 tachykinin receptors) on stimulus-evoked airway plasma exudation, bronchoconstriction and systemic hypotension in guinea-pigs in vivo. Plasma exudation was induced by substance P (SP), synthetic tachykinin receptor agonists, platelet activating factor (PAF), electrical stimulation of the cervical vagus nerves or by inhalation of cigarette smoke. Changes in airway tone and in carotid artery blood pressure (BP) were induced by synthetic tachykinin agonists, PAF and vagal stimulation. 2. Both FK224 and FK888 dose-dependently inhibited SP-induced plasma exudation in the lower trachea and main bronchi (ID50 values respectively of 1.1 and 0.1 mumol kg-1 in lower trachea, and of 0.5 and 0.1 mumol kg-1 in main bronchi) with complete inhibition at both airway levels at 10 mumol kg-1 for FK224 and at 2 mumol kg-1 for FK888. 3. The NK1-selective tachykinin receptor agonist, [Sar9,Met(O2)11]substance P ([Sar]SP), induced plasma exudation, a response which was blocked by both FK888 and FK224. The NK2-selective agonist, [beta-Ala8]neurokinin A-(4-10) ([beta-Ala]NKA), did not induce plasma exudation: neither FK888 nor FK224 affected this lack of response to [beta-Ala]NKA. 4. [beta-Ala]NKA induced bronchoconstriction, a response which was blocked by FK224 but which was completely unaffected by FK888. [Sar]SP induced a small but significant bronchoconstriction which was completely inhibited by both tachykinin antagonists. 5. In animals pretreated with capsaicin to deplete sensory neuropeptides, PAF induced both plasma exudation and bronchoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Studies on the vascular permeability induced by intrathecal substance P and bradykinin in the rat.

The effects of substance P (SP), SP fragments, neurokinin A (NKA), neurokinin B (NKB) and selective agonists for neurokinin receptors were assessed on cutaneous vascular permeability after intrathecal (i.t.) administration in rats. Dose-dependent increases in plasma extravasation were observed with the following rank orders of potency ([p-Glu6]SP-(6-11) greater than SP greater than or equal to SP-(4-11) greater than [p-Glu5,MePhe8,Sar9]SP-(5-11) = [p-Glu5]SP-(5-11) greater than SP-(7-11) and SP greater than NKA greater than NKB). The N-terminal fragments SP-(1-4), SP-(1-7) and SP-(1-9) were inactive up to 65 nmol. The NK-1 receptor selective agonists [( beta-Ala4,Sar9,Met(O2)11]SP-(4-11) and [Pro9,Met(O2)11]SP) were more potent than the NK-2 ([Nle10]NKA-(4-10] and NK-3 ([beta-Asp4,MePhe7]NKB-(4-10) and [MePhe7]NKB) receptor-selective agonists. Plasma extravasation was also increased by i.t. bradykinin (BK, 8.1 nmol) while the fragment BK-(1-8), a potent B1-receptor-selective agonist, produced only a slight effect at 81 nmol. When BK was given after prior i.t. administration of 6.1 nmol of [Thi5.8,D-Phe7]BK, an antagonist of BK at the B2-receptor, the increase in vascular permeability was significantly attenuated. The analogue [Leu8]BK-(1-8) (10.3 nmol), an antagonist of BK at the B1-receptor, failed to modify the BK-induced plasma extravasation. Plasma extravasation induced by SP (6.5 nmol) and BK (8.1 nmol) was abolished in cervically vagotomized rats, and significantly reduced in both spinal rats and in capsaicin-treated animals. Conversely, bilateral adrenalectomy (48 h earlier) and intercollicular decerebration (30 min earlier) had no major effect on the response elicited either by SP or BK. The response to SP remained unaffected by methysergide and hexamethonium but was significantly reduced by methylnitrate atropine and diphenhydramine. Indomethacin significantly enhanced the plasma extravasation induced by SP. These results suggest that SP and BK may play a role as spinal mediators in peripheral vascular permeability through a sensory and cholinergic vagal mechanism involving a spinobulbar pathway. The receptors mediating the response to SP and BK in the spinal cord are of the NK-1 and B2 subtypes, respectively.     

Respiratory actions of tachykinins in the nucleus of the solitary tract: effect of neonatal capsaicin pretreatment

1. The respiratory response to microinjection of capsaicin and tachykinin receptor agonists into the commissural nucleus of the solitary tract (cNTS) was investigated in adult, urethane-anaesthetized rats which had been pretreated with capsaicin (50 mg kg(-1) s.c.) or vehicle (10% Tween 80, 10% ethanol in saline) as day 2 neonates. 2. Microinjection of capsaicin (1 nmol) into the cNTS of vehicle-pretreated rats, significantly reduced respiratory frequency (59 breaths min(-1), preinjection control, 106 breaths min(-1)) without affecting tidal volume (VT). In capsaicin-pretreated rats, the capsaicin-induced bradypnoea was markedly attenuated (minimum frequency, 88 breaths min(-1); control, 106 breaths min(-1)). 3. In vehicle-pretreated rats, microinjection of substance P (SP, 33 pmol), neurokinin A (NKA, 33 pmol) and NKB (330 pmol), and the selective NK(1) tachykinin receptor agonists, [Sar(9), Met(O(2))(11)]-SP (33 pmol) and septide (10 pmol), increased VT (maxima, 3.60 - 3.93 ml kg(-1)) compared with preinjection control (2.82 ml kg(-1)), without affecting frequency. The selective NK(3) agonist senktide (10 pmol) also increased VT (3.93 ml kg(-1)) which was accompanied by a bradypnoea (-25 breaths min(-1)). The selective NK(2) agonist, [Nle(10)]-NKA(4-10) (330 pmol) increased VT slightly but significantly decreased frequency (-12 breaths min(-1)). In capsaicin-pretreated rats, VT responses to SP and [Sar(9), Met(O(2))(11)]-SP were increased whereas the response to septide was abolished. Both the VT and bradypnoeic responses to senktide and [Nle(10)]-NKA(4-10) were significantly enhanced. 4. These results show that neonatal capsaicin administration markedly reduces the respiratory response to microinjection of capsaicin into the cNTS. The destruction of capsaicin-sensitive afferents appears to sensitize the NTS to SP, NKB, [Sar(9),Met(O(2))(11)]-SP, senktide and [Nle(10)]-NKA(4-10). Moreover, the loss of septide responsiveness in capsaicin-pretreated rats, suggests that 'septide-sensitive' NK(1) receptors may be located on the central terminals of afferent neurons.     

The influence of the initial stretch and the agonist-induced tone on the effect of basal and stimulated release of EDRF.

1. The binding properties and pharmacological specificity of the selective NK3 tachykinin receptor agonist [3H))-senktide [( 3H]-succinyl[Asp6,MePhe8] substance P (6-11] have been examined in homogenates of guinea-pig ileum longitudinal muscle-myenteric plexus (LM/MP) and cerebral cortex. 2. Scatchard analysis of saturation binding studies in guinea-pig ileum LM/MP and cerebral cortex membranes indicated that [3H]-senktide bound to a single site with apparent high affinity, KD = 2.21 +/- 0.65 nM; Bmax = 13.49 +/- 0.04 fmol mg-1 protein in ileum and KD = 8.52 +/- 0.45 nM; Bmax = 76.3 +/- 1.6 fmol mg-1 protein in cortex (values are means +/- ranges; n = 2). 3. The pharmacological profile for tachykinins and analogues in displacing [3H]-senktide from ileum membranes was: [MePhe7] neurokinin B greater than neurokinin B (NKB) congruent to senktide greater than eledoisin greater than substance P (SP) greater than neurokinin A(NKA) greater than physalaemin greater than [Sar9,Met(O2)11]SP greater than [Nle10]NKA(4-10) = [Glp6,L-Pro9]-SP(6-11) greater than substance P methyl ester, consistent with [3H]-senktide binding to an NK3 subtype of tachykinin receptor. A similar rank order of affinity was obtained for these peptides in displacing [3H]-senktide from cortex membranes. 4. Several tachykinin receptor agonists were tested for their ability to displace [3H]-senktide from ileal and cortical NK3 binding sites and were found to be either weak displacers (pIC50 less than 5.00) or inactive.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence that tachykinins relax the guinea-pig trachea via nitric oxide release and by stimulation of a septide-insensitive NK1 receptor.

1. This study investigated the possibility that tachykinins relax the guinea-pig isolated trachea by releasing nitric oxide (NO) from the epithelium. The types of tachykinin receptor mediating both relaxation and contraction of the trachea were also studied. Isometric tension was recorded in isolated tracheal tube preparations precontracted with acetylcholine (10 microM) in which compounds were administered intraluminally in the presence of phosphoramidon and indomethacin (both 1 microM) and the tachykinin NK2 receptor antagonist, SR 48,968 ((S)-N-methyl-N[4-(4-acetyl amino-4-phenylpiperidino)-2-(3,4-dichlorophenyl)butyl]benzamide), 0.1 microM). 2. In the presence of the inactive enantiomer of an NO-synthase inhibitor, NG-monomethyl-D-arginine (D-NMMA, 100 microM), substance P (SP), neurokinin A (NKA), neurokinin B (NKB) and the selective NK1 receptor agonist, [Sar9, Met(O2)11]-SP, (0.1-10 nM) relaxed tracheal tube preparations. This relaxation was changed into a contraction by pretreatment with the NO-synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA, 100 microM). The effect of L-NMMA on SP- and [Sar9, Met(O2)11]-SP-induced responses was reversed by L-arginine (L-Arg, 1 mM), but not by D-Arg (1 mM). After removal of the epithelium SP, NKA and NKB and [Sar9, Met(O2)11]-SP (0.1-10 nM) evoked contractile responses in the presence of either L-NMMA (100 microM) or D-NMMA (100 microM). The effects of SP and [Sar9, Met(O2)11]-SP obtained in the presence of another NO-synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME, 100 microM) or its inactive enantiomer, NG-nitro-D-arginine methyl ester (D-NAME, 100 microM) were similar to those observed with L-NMMA or D-NMMA, respectively. 3. The selective NK1 receptor agonist, [pGlu6, Pro9]-SP(6-11) (septide, 0.1-10 nM) evoked contractile responses of tracheal tube preparations in the presence of either D-NMMA (100 microM) or L-NMMA (100 microM). The log concentration-response curve to septide obtained in the presence of L-NMMA was similar to that obtained in the presence of D-NMMA. [Sar9, Met(O2)11]-SP (0.1-10 nM) relaxed tracheal tube preparations precontracted with septide (1 microM), whereas septide (0.1 nM-1 microM) further contracted tracheal tube preparations precontracted with [Sar9, Met(O2)11]-SP (1 microM). 4. Relaxant and contractile responses evoked by SP, NKA, NKB and by [Sar9, Met(O2)11]-SP (0.1-10 nM) were not affected by a combination of the histamine H1 (pyrilamine, 1 microM) and H2 (cimetidine, 1 microM) receptor antagonists, but were abolished by the tachykinin NK1 receptor antagonist, CP-99,994 ((2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine, 1 microM), though not by its inactive enantiomer CP-100,263 (1 microM). Contractile responses evoked by septide (10 nM and 1 microM) were also abolished by CP-99,994 (1 microM) but not by CP-100,263 (1 microM). 5. These results demonstrate that tachykinins relax guinea-pig tracheal tube preparations by releasing NO via the stimulation of epithelial NK1 receptors by a mechanism independent of histamine release. The NK1 receptor type involved is sensitive to SP, NKA, NKB and [Sar9, Met(O2)11]-SP but not to septide, and is pharmacologically distinct from the NK1 receptor that mediates contraction, which is stimulated by all the agonists, including septide.     

Characterization of central and peripheral effects of septide with the use of five tachykinin NK1 receptor antagonists in the rat.

1. Effects of two tachykinin NK1 receptor selective agonists (septide and [Sar9, Met(O2)11]SP) were compared on the increases in mean arterial pressure (MAP), heart rate (HR) and motor behaviour following intracerebroventricular (i.c.v.) administration in unanaesthetized rat, and on the vascular permeability increases to intradermal (i.d.) injection in the anaesthetized rat. Moreover, five tachykinin NK1 receptor selective antagonists (LY303870, LY306740, LY303241, SR140333 and RP67580) were tested against the two agonists to compare their pharmacological profile. 2. [Sar9, Met(O2)11]SP and septide (10-100 pmol per rat, i.c.v.) were equipotent in increasing MAP and HR, yet they had dissimilar time-course. Both agonists increased dose-dependently face washing and sniffing while [Sar9, Met(O2)11]SP was the sole to produce grooming, septide was more potent than [Sar9, Met(O2)11]SP (6.5-650 pmol) in increasing vascular permeability. 3. For most centrally mediated responses, LY303870 and RP67580 were significantly more potent in inhibiting septide than [Sar9, Met(O2)11]SP. In some parameters, greater blockade was achieved when antagonists (particularly LY306740) were given 1 h instead of 10 min prior to i.c.v. septide. 4. All antagonists except LY303241 blocked dose-dependently the increases in vascular permeability to equipotent doses of [Sar9, Met(O2)11]SP and septide. LY303870 and LY306740 were more potent against septide. 5. The antagonism afforded by LY303870, LY306740 and LY303241 was stereoselective and only SR140333 was found to cause central and peripheral non specific effects. 6. The data confirm a distinct pharmacological profile for septide in vivo. RP67580 and LY306740 are currently the most valuable tachykinin NK1 receptor antagonists for in vivo studies in rat.     

Comparative behavioural profile of centrally administered tachykinin NK1, NK2 and NK3 receptor agonists in the guinea-pig.

1. The NK1 tachykinin receptor agonists, septide, [Sar9,Met(O2)11]SP and [Pro9]SP produced locomotor hyperactivity (10-20 min) when injected intracerebroventricularly (i.c.v.) in the guinea-pig. The most potent in eliciting this hyperactivity was septide (from 0.63 to 5 micrograms), compared to [Sar9,Met(O2)11]SP, which was active at 2.5 and 5 micrograms and [Pro9]SP which induced a non-significant increase even at 10 micrograms. 2. Wet-dog shakes were elicited by septide, [Sar9,Met(O2)11]SP and [Pro9]SP injected by the i.c.v. route in the guinea-pig. [Sar9,Met(O2)11]SP, active from 0.16 to 2.5 micrograms was more potent than septide (active at 1.25 micrograms) and [Pro9]SP (active at 0.63 micrograms) in eliciting such behaviour. To a lesser extent, grooming was also observed after injection of these agonists. 3. The NK2 tachykinin receptor agonist, [Lys5,MeLeu9,Nle10]NKA(4-10), up to the dose of 10 micrograms i.c.v. had no effect in the guinea-pig. It neither modified locomotor activity nor induced a characteristic behavioural response. At higher doses (20 micrograms), some toxic effects were noted. 4. The NK3 tachykinin receptor agonist, senktide, contrasts with the NK1 receptor agonists in that it elicited only wet-dog shakes, at doses ranging from 0.32 to 1.25 micrograms. It neither modified locomotor activity (1 microgram) nor induced grooming (up to 5 micrograms) in the guinea-pig. 5. To our knowledge, these results are the first demonstration that the guinea-pig could be useful to differentiate tachykinin agonists on the basis of their behavioural profile, distinct from those obtained in mice and rats.     

Characterization of receptors for kinins and neurokinins in the arterial and venous mesenteric vasculatures of the guinea-pig.

1. In the present work, we have studied the microvascular reactivity of the arterial and venous mesenteric beds of the guinea-pig to bradykinin, neurokinins and other agents. 2. The vasoactive properties of three selective agonists for neurokinin receptors, namely [Sar9, Met (O2)11]SP (NK1), [beta-Ala8]NKA(4-10) (NK2) and [MePhe7]NKB (NK3), were evaluated on precontracted arterial and venous mesenteric vasculatures of the guinea-pig. The NK1-selective agonist, [Sar9,Met(O2)11]SP (1 to 1000 pmol), induced an endothelium-dependent and N omega-nitro-L-arginine methyl ester (L-NAME)-sensitive relaxation of the arterial vasculature precontracted with methoxamine, whereas the NK2 and NK3-selective agonists were virtually inactive at high doses (1000 pmol). 3. The three selective neurokinin receptor agonists were inactive in the non-precontracted arterial and venous mesenteric vasculatures as well as in the precontracted venous mesenteric vasculature. 4. Bradykinin (0.1 to 100 pmol) induced a marked dose- and endothelium-dependent vasodilatation of the precontracted arterial and venous vasculatures. ED50 values were 5.5 pmol on the arterial side and 1.9 pmol on the venous side. In contrast, desArg9-bradykinin was inactive at doses up to 1000 pmol. Furthermore, on the arterial and venous sides, a higher dose of bradykinin (1000 pmol), induced a biphasic effect, a transient constriction followed by a marked and sustained vasodilatation. The vasodilator effects of bradykinin were abolished by Hoe 140 (0.1 microM) and CHAPS, markedly reduced by L-NAME and were unaffected by [Leu8]desArg9-bradykinin (0.1 microM) on both sides of the mesenteric vasculature. Hoe 140 also abolished the arterial vasoconstrictions induced by high doses of bradykinin.(ABSTRACT TRUNCATED AT 250 WORDS)