Colorectal and cardiovascular effects of [Lys5,MeLeu9,Nle10]-NKA(4-10) in anesthetized macaques.

The effects of the tachykinin NK2 receptor agonist LMN-NKA ([Lys5,MeLeu9,Nle10]-NKA(4-10)) on colorectal and arterial blood pressure were examined in anesthetized macaques. Intravenous (IV) administration of 1-100 µg/kg caused dose-related increases in colorectal pressure up to 120 mmHg above baseline, and area under the curve (AUC) up to 24,987 mmHg*s. This was accompanied at all doses by transient hypotension, with up to 26% reduction in mean arterial pressure (MAP) from baseline. Hypotension, but not the increase in colorectal pressure, was inhibited by a 10-min pretreatment with the NK1 receptor antagonist CP-99,994. In a pilot experiment using subcutaneous (SC) injection, a similar dose range of LMN-NKA (3-100 µg/kg) again appeared to increase colorectal pressure with a similar AUC (up to 18,546 mmHg*s) to that seen after IV injection, but lower peak amplitude (up to 49 mmHg). Unlike the effects of IV injection, hypotension was only present after the highest SC dose (100 µg/kg) in one of two animals. Pharmacokinetic analysis revealed markedly lower plasma exposures after SC compared with IV administration. Cmax was 39.6 versus 1070 ng/mL, and AUCinf was 627 versus 2090 ng/mL*min, respectively. These findings are consistent with previous observations in anesthetized dogs and indicate that the prokinetic effects of LMN-NKA may be achieved without hypotension using a route of administration that avoids unnecessarily high plasma exposures.

Do Substance P and Neurokinin A Play Important Roles in the Control of LH Secretion in Ewes?

There is now general agreement that neurokinin B (NKB) acts via neurokinin-3-receptor (NK3R) to stimulate secretion of GnRH and LH in several species, including rats, mice, sheep, and humans. However, the roles of two other tachykinins, substance P (SP) and neurokinin A, which act primarily via NK1R and NK2R, respectively, are less clear. In rodents, these signaling pathways can stimulate LH release and substitute for NKB signaling; in humans, SP is colocalized with kisspeptin and NKB in the mediobasal hypothalamus. In this study, we examined the possible role of these tachykinins in control of the reproductive axis in sheep. Immunohistochemistry was used to describe the expression of SP and NK1R in the ovine diencephalon and determine whether these proteins are colocalized in kisspeptin or GnRH neurons. SP-containing cell bodies were largely confined to the arcuate nucleus, but NK1R-immunoreactivity was more widespread. However, there was very low coexpression of SP or NK1R in kisspeptin cells and none in GnRH neurons. We next determined the minimal effective dose of these three tachykinins that would stimulate LH secretion when administered into the third ventricle of ovary-intact anestrous sheep. A much lower dose of NKB (0.2 nmol) than of neurokinin A (2 nmol) or SP (10 nmol) consistently stimulated LH secretion. Moreover, the relative potency of these three neuropeptides parallels the relative selectivity of NK3R. Based on these anatomical and pharmacological data, we conclude that NKB-NK3R signaling is the primary pathway for the control of GnRH secretion by tachykinins in ewes.

Effects of intravenous administration of neurokinin receptor subtype-selective agonists on gonadotropin-releasing hormone pulse generator activity and luteinizing hormone secretion in goats.

Recent evidence suggests that neurokinin B (NKB), a member of the neurokinin (tachykinin) peptide family, plays a pivotal role in gonadotropin-releasing hormone (GnRH) pulse generation. Three types of neurokinin receptors (NKRs), NK1R, NK2R and NK3R, are found in the brain. Although NKB preferentially binds to NK3R, other NKRs are possibly also involved in NKB action. The present study examined the effects of intravenous administration of the NKR subtype-selective agonists GR73632 (NK1R), GR64349 (NK2R), and senktide (NK3R) on GnRH pulse generator activity and luteinizing hormone (LH) secretion. Multiple-unit activity (MUA) was monitored in ovariectomized goats (n = 5) implanted with recording electrodes. Characteristic increases in MUA (MUA volleys) were considered GnRH pulse generator activity. Although three NKR agonists dose-dependently induced an MUA volley and an accompanying increase in LH secretion, the efficacy in inducing the volley markedly differed. As little as 10 nmol of senktide induced an MUA volley in all goats, whereas a dose of 1000 nmol was only effective for the NK1R and NK2R agonists in two and four goats, respectively. When the treatment failed to evoke an MUA volley, no apparent change was observed in the MUA or LH secretion. Similar effects of the NK2R and NK3R agonists were observed in the presence of estradiol. The results demonstrated that NK3R plays a predominant role in GnRH pulse generation and suggested that the contributions of NK1R and NK2R to this mechanism may be few, if any, in goats.

Role of tachykinins and neurokinin receptor subtypes in the regulation of motility of the forestomach and abomasum in conscious sheep.

The present study was planned to evaluate role of tachykinins (TKs) and neurokinin (NK) receptors in the regulation of gastric motility in sheep. We examined the effects of intravenous (i.v.) injection of neurokinin A (NKA) and substance P (SP) on motility of the rumen, omasum, and abomasum in conscious sheep and the effects of NK receptor blockade on the effect of TKs using NK-1 receptor antagonist L-732,138 and NK-2 receptor antagonist SR48968. Moreover, the effect of NK receptor blockade on omasal cyclic contractions was examined. Intravenous injection of NKA and SP induced tonic contraction of rumen, omasum, and abomasum, and the contractile effect of NKA was more potent than that of SP in all the gastric regions. Although the effect of SP was not inhibited by L-732,138, the effect of NKA was significantly inhibited by SR48968. However, single infusion of SR48968 and L-732,138 did not alter cyclic electromyographic activity and basal intraluminal pressure in the omasum. These results imply that NKA and NK-2 receptors play a primary role in non-cholinergic regulation of ovine gastric motility, though NK-2 and NK-1 receptors seem unlikely to be involved in the physiological regulation of omasal cyclic contractions.

Neurokinin2-R in medial septum regulate hippocampal and amygdalar ACh release induced by intraseptal application of neurokinins A and B.

The neurokinin receptors (NK-R), NK(2)- and NK(3)-R, have been implicated in behavioral processes, but apparently in opposite ways: while NK(2)-R agonism disrupts memory and has anxiogenic-like action, NK(3) -R agonists facilitate memory and display anxiolytic-like effects. Systemic application of NK(2)-R antagonists block the release of acetylcholine (ACh) in the hippocampus, which is induced by intraseptal administration of the NK(2)-R ligand, neurokinin A (NKA). We investigated the effects of medial septal injection of NKA and a preferred ligand of NK(3)-R, neurokinin B (NKB), on the activity of cholinergic neurons of the basal forebrain and assessed the role of the medial septal NK(2)-R in the control of extracellular ACh levels in cholinergic projection areas. ACh was dialysed in the frontal cortex, amygdala and hippocampus of anesthetized animals and was analysed by HPLC-EC. ACh levels in hippocampus and amygdala, but not in frontal cortex were increased after intraseptal injection of either NKA or NKB (0.1, 1, 10 µM). Application of the nonpeptidic NK(2)-R antagonist, saredutant SR48968 (1, 10, 100 pM), followed by NKA (1 µM) or NKB (10 µM) injection into the medial septum, blocked the ACh increase in hippocampus and amygdala. These results indicate that medial septal NK(2)-R have an important role in mediating ACh release, for one, via the septal-hippocampal cholinergic projection and, secondly, via direct or indirect route to the amygdala, but not frontal cortex. They also support the hypothesis that hippocampal cholinergic neurotransmission controls amygdala function suggesting that this interaction is regulated via NK(2)-R in the medial septum.

Depression of cough reflex by microinjections of antitussive agents into caudal ventral respiratory group of the rabbit.

We have previously shown that the caudal nucleus tractus solitarii is a site of action of some antitussive drugs and that the caudal ventral respiratory group (cVRG) region has a crucial role in determining both the expiratory and inspiratory components of the cough motor pattern. These findings led us to suggest that the cVRG region, and possibly other neural substrates involved in cough regulation, may be sites of action of antitussive drugs. To address this issue, we investigated changes in baseline respiratory activity and cough responses to tracheobronchial mechanical stimulation following microinjections (30-50 nl) of some antitussive drugs into the cVRG of pentobarbital-anesthetized, spontaneously breathing rabbits. [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO) and baclofen at the lower concentrations (0.5 mM and 0.1 mM, respectively) decreased cough number, peak abdominal activity, and peak tracheal pressure and increased cough-related total cycle duration (Tt). At the higher concentrations (5 mM and 1 mM, respectively), both drugs abolished the cough reflex. DAMGO and baclofen also affected baseline respiratory activity. Both drugs reduced peak abdominal activity, while only DAMGO increased Tt, owing to increases in expiratory time. The neurokinin-1 (NK(1)) receptor antagonist CP-99,994 (10 mM) decreased cough number, peak abdominal activity, and peak tracheal pressure, without affecting baseline respiration. The NK(2) receptor antagonist MEN 10376 (5 mM) had no effect. The results indicate that the cVRG is a site of action of some antitussive agents and support the hypothesis that several neural substrates involved in cough regulation may share this characteristic.

Oxytocin release from the rat neurohypophysis into the blood: effects of tachykinin NK-1 and NK-2 receptors agonists and antagonists.

The aim of the present study was to investigate the effect of peptide NK-1 and NK-2 receptors agonists and antagonists (and their natural ligands, i.e., substance P and neurokinin A) on the oxytocin (OT) secretion from the rat neurohypophysis into the blood. Intracerebroventricular (icv) injection of substance P (SP) or highly selective NK-1 receptor agonist--[(Sar(9),Met(O2)(11))-Substance P]-- significantly stimulated the OT secretion from the rat neurohypophysis into the general circulation. After icv injection of the NK-1 receptor antagonist--[(Tyr(6),D-Phe(7),D-His(9))-Substance P (6-11)]--the blood plasma OT concentration was significantly lower, when compared to vehicle-injected animals. On the other hand, the icv administered neurokinin A (NKA) and the NK-2 receptor agonist--[(beta-Ala(8))-Neurokinin A (4-10)]--were essentially inactive in modifying OT secretion. However, such injection of the NK-2 receptor antagonist--[(Tyr(5),D-Trp(6,8,9),Lys-NH2(10))-Neurokinin A (4-10)]--was found to diminish the blood plasma hormone concentration, when compared to vehicle-injected animals. The neurohypophysial content of OT was decreased in NKA-treated rats, but neither the NK-2 receptor agonist nor antagonist were able to affect the OT output from the rat posterior pituitary. The hypothalamic levels of OT were not modified by any of the studied peptides. The present data strongly indicate a major role for the tachykinin NK-1 receptor in SP- and/or NKA-dependent regulation of OT secretion from the rat neurohypophysis into the blood.

Contractile properties of the pig bladder mucosa in response to neurokinin A: a role for myofibroblasts?

BACKGROUND AND PURPOSE: The bladder urothelium is now known to have active properties. Our aim was to investigate the contractile properties of the urinary mucosa in response to the tachykinin neurokinin A (NKA) and carbachol. EXPERIMENTAL APPROACH: Discrete concentration-response curves for carbachol and NKA were obtained in matched strips of porcine detrusor, mucosa and intact bladder, suspended in organ baths. The effects of inhibitors and tachykinin receptor antagonists were studied on NKA-mediated contractions in mucosal strips. Intact sections of bladder and experimental strips were processed for histology and immunohistochemistry. KEY RESULTS: All types of strips contracted to both carbachol and NKA. Mucosal responses to NKA (pD2 7.2) were higher than those in intact strips and were inhibited by the NK2 receptor antagonist SR48968 (pKB 9.85) but not the NK1 receptor antagonist SR140333, tetrodotoxin or indomethacin. Immunostaining for smooth muscle actin and vimentin occurred under the urothelium and on blood vessels. Desmin immunostaining and histological studies showed only sparse smooth muscle to be present in the mucosal strips. Removal of smooth muscle remnants from mucosal strips did not alter the responses to NKA. CONCLUSIONS AND IMPLICATIONS: This study has shown both functional and histological evidence for contractile properties of the mucosa, distinct from the detrusor. Mucosal contractions to NKA appear to be directly mediated via NK2 receptors. The main cell type mediating mucosal contractions is suggested to be suburothelial myofibroblasts. Mucosal contractions may be important in vivo for matching the luminal surface area to bladder volume.

Ventilatory and cardiovascular actions of centrally administered trout tachykinins in the unanesthetized trout.

The brains of teleost fish contain members of the tachykinin family that are the products of orthologous genes expressed in mammalian nervous tissues, but little is known regarding the physiological effects of these peptides in their species of origin. The present study compares the central actions of trout neuropeptide gamma (NPgamma), substance P (SP) and neurokinin A (NKA) (5-250 pmol) on ventilatory and cardiovascular parameters in the unanesthetized rainbow trout Oncorhynchus mykiss. Intracerebroventricular (ICV) injection of NPgamma evoked a dose-dependent elevation of the ventilation rate (f(V)) but a reduction of the ventilation amplitude (V(AMP)) that was caused by a reduction of the magnitude of the adduction phase of the ventilatory signal. The net effect of NPgamma was to produce an hypoventilatory response since the total ventilation (V(TOT)) was significantly reduced. The minimum effective dose for a significant effect of NPgamma on f(V) and V(AMP) was 50 pmol. SP evoked a significant elevation of f(V), a concomitant depression of V(AMP), and a resultant decrease in V(TOT) but only at the highest dose (250 pmol). NKA was without action on f(V) but significantly decreased V(AMP) at only the highest dose tested. In this case also, the net effect of NKA was to reduce V(TOT). When injected centrally, none of the three peptides, at any dose tested, produced changes in heart rate or mean dorsal aortic blood pressure (P(DA)). Intra-arterial injection of the three tachykinins (250 pmol) produced a significant (P<0.05) increase in P(DA), but only SP and NKA induced concomitant bradycardia. None of the three peptides produced any change in f(V) or V(AMP). In conclusion, our results demonstrate that centrally injected tachykinins, particularly NPgamma, produce a strong hypoventilatory response in a teleost fish and so suggest that endogenous tachykinins may be differentially implicated in neuroregulatory control of ventilation.

Intrathecally administered D-cycloserine produces nociceptive behavior through the activation of N-methyl-D-aspartate receptor ion-channel complex acting on the glycine recognition site.

Intrathecal (i.t.) administration of D-cycloserine (100 and 300 fmol), a partial agonist of the glycine recognition site on the N-methyl-D-aspartate (NMDA) receptor ion-channel complex, produced a behavioral response mainly consisting of biting and/or licking of the hindpaw and the tail along with slight hindlimb scratching directed toward the flank in mice, which peaked at 5 - 10 min and almost disappeared at 15 min after the injection. The behavior induced by D-cycloserine (300 fmol) was dose-dependently inhibited by an intraperitoneal injection of morphine (0.5-2 mg/kg), suggesting that the behavioral response is related to nociception. The nociceptive behavior was also dose-dependently inhibited by i.t. co-administration of 7-chlorokynurenic acid (0.25-4 nmol), a competitive antagonist of the glycine recognition site on the NMDA receptor ion-channel complex; D-(-)-2-amino-5-phosphonovaleric acid (62.5-500 pmol), a competitive NMDA receptor antagonist; MK-801 (62.5-500 pmol), an NMDA ion-channel blocker; ifenprodil (0.5-8 nmol); arcaine (31-125 pmol); and agmatine (0.1-10 pmol), all being antagonists of the polyamine recognition site on the NMDA receptor ion-channel complex. However, [D-Phe7,D-His9]-substance P(6-11), a specific antagonist for substance P (NK1) receptors, and MEN-10,376, a tachykinin NK2-receptor antagonist, had no effect on D-cycloserine-induced nociceptive behavior. These results in the mouse spinal cord suggest that D-cycloserine-induced nociceptive behavior is mediated through the activation of the NMDA receptor ion-channel complex by acting on the glycine recognition site and that it does not involve the tachykinin receptor mechanism.

Intrathecal administration of neurokinin 1 and neurokinin 2 receptor antagonists undermines the savings effect in spinal rats seen in an instrumental learning paradigm.

Research has demonstrated that the isolated spinal cord is capable of modifying its behavior in response to changes in environmental stimuli. Previous studies have shown that rats with complete thoracic spinal transections can learn to maintain a flexion response when shock delivery is paired with leg position. The current experiments examined whether neurokinin (NK) 1 and 2 receptors are involved in the acquisition and retention of this prolonged flexion response. Results demonstrated that L-703,606 (NK1 antagonist) facilitated response acquisition, whereas MEN-10,376 (NK2 antagonist) hindered acquisition. Furthermore, pretraining administration of either antagonist undermined subjects' ability to reacquire the prolonged flexion response during testing. These results demonstrate the importance of NK receptors in spinally mediated behavioral plasticity.

Dual tachykinin NK1/NK2 antagonist DNK333 inhibits neurokinin A-induced bronchoconstriction in asthma patients.

Inhalation of neurokinin A (NKA) causes bronchoconstriction in patients with asthma. In vitro both tachykinin NK1 and NK2 receptors can mediate airway contraction. In this study the authors examined the effects of a single dose of the dual tachykinin NK1/NK2 receptor antagonist, DNK333, on NKA-induced bronchoconstriction in asthma. A total of 19 male adults with mild asthma completed a randomised, double-blind, placebo-controlled crossover trial. Increasing concentrations of NKA (3.3x10(-9) to 1.0x10(-6) mol x mLP(-1)) were inhaled at 1 and 10 h intervals after a single oral dosing with either DNK333 (100 mg) or a placebo. It was observed that DNK333 did not affect baseline lung function but did protect against NKA-induced bronchoconstriction in those patients. The mean log10 provocative concentration causing a 20% fall in forced expiratory volume in one second for NKA was -5.6 log10 mol x mL(-1) at 1 h after DNK333 treatment and -6.8 log10 mol x mL(-1) after placebo. This was equivalent to a difference of 4.08 doubling doses, which decreased to a difference of 0.90 doubling doses 10 h after treatment. The results shown in this report indicate that DNK333 blocks neurokinin A-induced bronchoconstriction in patients with asthma.

Effect of inhaled fluticasone on bronchial responsiveness to neurokinin A in asthma.

Neurokinin (NK) A causes airway narrowing in patients with asthma through direct and indirect mechanisms. The effects of the inhaled glucocorticosteroid fluticasone propionate (FP) on the bronchial responsiveness to NKA and methacholine were studied. Patients (n=11) with mild asthma participated in a randomized, double-blind, placebo-controlled crossover trial. FP (500 microg b.i.d.) or matched placebo was administered via Diskhaler for 14 days. Bronchial challenges were performed on days 1 and 13 (methacholine) and 0 and 14 (NKA) for each treatment period. At the active treatment period, the mean log2 provocative concentration causing a 20% fall in the forced expiratory volume in one second (PC20)+/-SEM for NKA was -12.72+/-0.63 at the beginning and -9.77+/-0.49 at the end of the period (p<0.0001), while under placebo, it was -12.16+/-0.82 and -12.19+/-0.51 respectively (NS). At the active treatment period, the mean log2 PC20 for methacholine was -5.25+/-0.40 at the beginning and -4.22+/-0.31 at the end of the period (p=0.012), while under placebo, it was -5.47+/-0.47 and -5.24+/-0.42 respectively (NS). The reduction in response to NKA was significantly larger than that for methacholine. A 2-week course of an inhaled steroid reduces bronchial responsiveness to neurokinin A, an effect more pronounced than the reduction in bronchial responsiveness to methacholine.

Tachykinin-induced stimulation of neuropeptide Y gene expression in the rat arcuate nucleus.

Previous neurocytochemical data indicate the presence of synaptic contacts between tachykinergic terminals and neuropeptide Y (NPY) neurons in the arcuate nucleus of the rat suggesting that tachykinins may regulate NPY neuronal activity. To examine the functional signification of such regulation, the effect of intracerebroventricular administration of neurokinin A on NPY mRNA levels was studied using in situ hybridization. Repeated treatment with NKA (40 microg/day for 3 days) induced a 44% increase in NPPY mRNA expression compared with saline-injected control animals. These results demonstrate a positive effect of tachykinins on NPY gene expression and suggest either a direct or indirect control of arcuate NPY neurons by endogenous tachykinins.

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.

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.

Role of nitric oxide and septide-insensitive NK(1) receptors in bronchoconstriction induced by aerosolised neurokinin A in guinea-pigs.

The tachykinin, neurokinin A (NKA), contracts guinea-pig airways both in vitro and in vivo, preferentially activating smooth muscle NK(2) receptors, although smooth muscle NK(1) receptors may also contribute. In vitro evidence suggests that NKA activates epithelial NK(1) receptors, inducing the release of nitric oxide (NO) and subsequent smooth muscle relaxation. A number of selective NK(1) receptor agonists have been reported to activate both smooth muscle and epithelial NK(1) receptors, however septide appears only to activate smooth muscle NK(1) receptors. The aim of the present study was to investigate whether NKA-induced bronchoconstriction in guinea-pigs in vivo may be limited by NO release via NK(1) receptor activation, and whether selective NK(1) receptor agonists may activate this mechanism differently. Aerosolized NKA caused an increase in total pulmonary resistance (RL) that was markedly reduced by the NK(2) receptor antagonist, SR 48968, and abolished by the combination of SR 48968 and the NK(1) receptor antagonist, CP-99, 994. The increase in RL evoked by NKA was potentiated by pretreatment with the NO synthase (NOs) inhibitor, L-NAME, but not by the inactive enantiomer D-NAME. Potentiation by L-NAME of NKA-induced increase in RL was reversed by L-Arginine, but not by D-Arginine. Pretreatment with L-NAME did not affect the increase in RL induced by the selective NK(2) receptor agonist, [beta-Ala(8)]NKA(4-10), and by the selective NK(1) receptor agonist, septide, whereas it markedly potentiated the increase in RL caused by a different NK(1) selective agonist, [Sar(9),Met(O(2))(11)]SP. Dose-response curves showed that septide was a more potent bronchoconstrictor than [Sar(9),Met(O(2))(11)]SP to cause bronchoconstriction. Pretreatment with the NK(1) receptor antagonist, CP-96,994, abolished the ability of L-NAME to increase bronchoconstriction to aerosolized NKA. Bronchoconstriction to aerosolized NKA was increased by L-NAME, after pretreatment with the NK(3) receptor antagonist, SR 142801. The present study shows that in vivo bronchoconstriction in response to the aerosolized naturally occurring tachykinin, NKA, is limited by its own ability to release relaxant NO via NK(1) receptor activation. This receptor is apparently insensitive to septide, thus justifying, at least in part, the high potency of septide to cause bronchoconstriction in guinea-pigs.

Tachykinin NK(3)receptor involvement in anxiety.

This study investigates the effects of intracerebroventricular injection of selective agonists and antagonists of tachykinin NK(3)receptor on performance of mice in the elevated plus-maze test. Mice were treated with either vehicle or 1, 10, 100 or 500 pmol of neurokinin B or senktide ([succinil-Asp(6), MePhe(8)]substance P(6-11), a natural and synthetic selective NK(3)receptor agonists, respectively. Other mice received similar doses of [Trp(7)beta-Ala(8)]NKA(4-10)or SR 142801 ((S)-N-(1-(3-(1-benzoyl-3-(3, 4-dichlorophenyl)-piperidin-3-yl)propyl)-4-phenyl-piperidin- 4-yl)-N-m ethylacetamide) tachykinin NK(3)receptor selective peptide and non-peptide antagonists, respectively. Senktide significantly increased the frequency of entries and the time spent in the open arms, which is compatible with an anxiolytic action. Neurokinin B treatment did not alter the plus-maze parameters in a significant way. Conversely, the NK(3)peptide antagonist [Trp(7)beta-Ala(8)]NKA(4-10), but not SR142801 non-peptide antagonist, showed a reverse effect, i.e. an anxiogenic profile of action, reducing the frequency and the time spent in the open arms. Co-injection of either senktide plus [Trp(7)beta-Ala(8)]NKA((4-10)), or senktide plus SR 142801, blocked the effects promoted by senktide, indicating that centrally-administered NK(3)receptor agonists and antagonists can modulate experimental anxiety.

Interaction between neurokinin A, VIP, prostanoids, and enteric nerves in regulation of duodenal function.

Neurokinin A (NKA) induces duodenal motility and increases mucosal permeability and bicarbonate secretion in the in situ perfused duodenum in anesthetized rats. In the present study, the NKA-induced increase in mucosal permeability was potentiated by luminal perfusion with lidocaine and diminished by vasoactive intestinal peptide (VIP) but unaltered by elevated intraluminal pressure. Elevation of intraluminal pressure, however, potentiated the stimulatory effect of NKA on bicarbonate secretion. In contrast, the tachykinin decreased the rate of alkalinization in rats subjected to elevated intraluminal pressure and treated with indomethacin. Similarly, NKA partially inhibited the VIP-stimulated bicarbonate secretion. Luminal lidocaine did not affect the secretory response to NKA. The motility induced by NKA was unaffected by VIP or lidocaine but decreased by elevated intraluminal pressure. It is concluded that the NKA-induced increase in duodenal mucosal bicarbonate secretion is independent of neurons and possibly mediated by prostanoids. The increase in mucosal permeability in response to NKA may be suppressed by mucosal nerves, perhaps utilizing VIP as one of the transmitters.

Neurokinin A increases duodenal mucosal permeability, bicarbonate secretion, and fluid output in the rat.

The aim of this study was to examine the integrative response to neurokinin A (NKA) on duodenal mucosal permeability, bicarbonate secretion, fluid flux, and motility in an in situ perfusion model in anesthetized rats. Intravenous infusion of NKA (100, 200, and 400 pmol.kg-1.min-1) induced duodenal motility. Furthermore, duodenal mucosal bicarbonate secretion, fluid output, and mucosal permeability increased in response to NKA. Pretreatment with the nicotinic antagonist hexamethonium did not change the response in any of the parameters investigated, whereas the NK2-receptor antagonist MEN 10,627 effectively inhibited all responses to NKA. Indomethacin induced duodenal motility and stimulated bicarbonate secretion. In indomethacin-treated rats, NKA further increased motility but decreased indomethacin-stimulated bicarbonate secretion by 70%. The NKA-induced increase in mucosal permeability was unaltered by indomethacin. It is concluded that NKA not only induces motility but also increases mucosal permeability and fluid output. Furthermore, the neuropeptide may have both stimulative and inhibitory effects on bicarbonate secretion. All responses to NKA are dependent on NK-2 receptor activation but are not mediated through nicotinic receptors.