Endogenous substance P modulates human cardiovascular regulation at rest and during orthostatic load

Effect of endogenous substance P on visceral afferent signal integration in the nucleus tractus solitaries of rat brainstem slices

In the first synapse of the blood-pressure-regulating pathway, a neurokinin (NK) family peptide substance P (SP) is release with an excitatory neurotransmitter, glutamate, to enhance the sensitivity of the baroreflex responses. However, the underlying mechanisms of action are not yet well understood. The effects of NK receptor antagonists and agonists on solitary tract stimulation-evoked excitatory postsynaptic responses were recorded using whole-cell patch-clamp recordings of neurons in the medial portion of the nucleus tractus solitarius (mNTS) in the brainstem. SP reduced the amplitude of the evoked excitatory postsynaptic currents (eEPSCs) and shifted the holding current inward, in a dose-dependent manner. The concentrations of SP needed to induce such responses were different between capsaicin-sensitive unmyelinated (C-type) and capsaicin-resistant myelinated (A-type) neurons. The perfusion of a NK1 receptor antagonist, sendide, reduced the amplitude of eEPSCs in all tested neurons but did not affect the levels of the holding current. A Neurokinin type 1 receptor (NK1 receptor) agonist, [Sar9, Met(O2)11]-SP, reduced the amplitude of the eEPSCs and shifted the holding current inward in capsaicin-resistant neurons; however, it failed to induce any significant changes in the capsaicin-sensitive neurons. Furthermore, a selective Neurokinin type 3 receptor (NK3 receptor) antagonist, SB223412, failed to induce any changes in any tested neuron. In current-clamp experiments, sendide reduced solitary tract (ST)-stimulation evoked firing of action potentials in both A- and C-type neurons. [Sar9, Met(O2)11]-SP suppressed the firing of the action potentials in C-type but not A-type neurons. In spontaneous synaptic recordings, SP reduced frequency of the sEPSCs in CAP sensitive neuron but NK1 agonist reduced at capsaicin resistant neurons. Taken together, the findings show that ST activation leads to the co-transmission of SP and glutamate and enhances baroreflex sensitivity by potentiating the amplitude of eEPSC in an NK1 receptor activity-dependent manner.

Anti-Diabetic Therapy and Heart Failure: Recent Advances in Clinical Evidence and Molecular Mechanism

Diabetic patients have a two- to four-fold increase in the risk of heart failure (HF), and the co-existence of diabetes and HF is associated with poor prognosis. In randomized clinical trials (RCTs), compelling evidence has demonstrated the beneficial effects of sodium-glucose co-transporter-2 inhibitors on HF. The mechanism includes increased glucosuria, restored tubular glomerular feedback with attenuated renin-angiotensin II-aldosterone activation, improved energy utilization, decreased sympathetic tone, improved mitochondria calcium homeostasis, enhanced autophagy, and reduced cardiac inflammation, oxidative stress, and fibrosis. The RCTs demonstrated a neutral effect of the glucagon-like peptide receptor agonist on HF despite its weight-reducing effect, probably due to it possibly increasing the heart rate via increasing cyclic adenosine monophosphate (cAMP). Observational studies supported the markedly beneficial effects of bariatric and metabolic surgery on HF despite no current supporting evidence from RCTs. Bromocriptine can be used to treat peripartum cardiomyopathy by reducing the harmful cleaved prolactin fragments during late pregnancy. Preclinical studies suggest the possible beneficial effect of imeglimin on HF through improving mitochondrial function, but further clinical evidence is needed. Although abundant preclinical and observational studies support the beneficial effects of metformin on HF, there is limited evidence from RCTs. Thiazolidinediones increase the risk of hospitalized HF through increasing renal tubular sodium reabsorption mediated via both the genomic and non-genomic action of PPARγ. RCTs suggest that dipeptidyl peptidase-4 inhibitors, including saxagliptin and possibly alogliptin, may increase the risk of hospitalized HF, probably owing to increased circulating vasoactive peptides, which impair endothelial function, activate sympathetic tones, and cause cardiac remodeling. Observational studies and RCTs have demonstrated the neutral effects of insulin, sulfonylureas, an alpha-glucosidase inhibitor, and lifestyle interventions on HF in diabetic patients.

Cardioprotective action of aprepitant in a rat model of ischemia-reperfusioninduced myocardial injury: role of PI3K-AkT-GSK-3β-HIF-1α signaling pathway

PURPOSE

The present study explored the role and mechanism involved in aprepitant-induced cardioprotective effects in rat model of ischemia-reperfusion injury.

METHODS

The isolated hearts of Wistar male albino rats were subjected to ischemia-reperfusion injury on Langendorff apparatus. The extent of myocardial injury was assessed by measuring lactate dehydrogenase 1 and CK-MB release in the coronary effluent. The rats were treated with aprepitant (5, 10 and 20 mg/kg) before isolating hearts. After injury, the levels of HIF-1α, p-AkT, p-GSK-3β/GSK-3β were measured in heart homogenates. LY294002 was employed as PI3K inhibitor.

RESULTS

Ischemia-reperfusion led to significant myocardial injury and decreased the levels of HIF-1α, p-AkT and ratio of p-GSK-3β/GSK-3β. Aprepitant attenuated myocardial injury and restored the biochemical changes in a dose-dependent manner. Pre-treatment with LY294002 (10 and 20 mg/kg) abolished aprepitant-mediated cardioprotective effects and restored the biochemical parameters in the heart homogenate.

CONCLUSIONS

Aprepitant may be effective in preventing ischemia-reperfusion-induced myocardial injury, which may be due to activation of PI3K-AkT-GSK-3β and HIF-1α signaling pathway.

Self-assembling peptide gels promote angiogenesis and functional recovery after spinal cord injury in rats

Spinal cord injury (SCI) leads to disruption of the blood–spinal cord barrier, hemorrhage, and tissue edema, which impair blood circulation and induce ischemia. Angiogenesis after SCI is an important step in the repair of damaged tissues, and the extent of angiogenesis strongly correlates with the neural regeneration. Various biomaterials have been developed to promote angiogenesis signaling pathways, and angiogenic self-assembling peptides are useful for producing diverse supramolecular structures with tunable functionality. RADA16 (Ac-RARADADARARADADA-NH2), which forms nanofiber networks under physiological conditions, is a self-assembling peptide that can provide mechanical support for tissue regeneration and reportedly has diverse roles in wound healing. In this study, we applied an injectable form of RADA16 with or without the neuropeptide substance P to the contused spinal cords of rats and examined angiogenesis within the damaged spinal cord and subsequent functional improvement. Histological and immunohistochemical analyses revealed that the inflammatory cell population in the lesion cavity was decreased, the vessel number and density around the damaged spinal cord were increased, and the levels of neurofilaments within the lesion cavity were increased in SCI rats that received RADA16 and RADA16 with substance P (rats in the RADA16/SP group). Moreover, real-time PCR analysis of damaged spinal cord tissues showed that IL-10 expression was increased and that locomotor function (as assessed by the Basso, Beattie, and Bresnahan (BBB) scale and the horizontal ladder test) was significantly improved in the RADA16/SP group compared to the control group. Our findings indicate that RADA16 modified with substance P effectively stimulates angiogenesis within the damaged spinal cord and is a candidate agent for promoting functional recovery post-SCI.

Mechanism by which dipeptidyl peptidase-4 inhibitors increase the risk of heart failure and possible differences in heart failure risk

Dipeptidyl peptidase-4 (DPP-4) inhibitors are oral antidiabetic drugs that safely reduce the blood glucose level over the long term. In Japan, DPP-4 inhibitors have become the oral antidiabetic drugs most frequently prescribed for patients with type 2 diabetes. However, the results of several cardiovascular outcomes studies have suggested that some DPP-4 inhibitors may increase the risk of hospitalization for heart failure. In patients with diabetes, heart failure is the most frequent cardiovascular condition, and it has a negative impact on the quality of life as well as being a potentially fatal complication. Therefore, it is important to determine whether an increased risk of heart failure is associated with certain DPP-4 inhibitors or is a class effect of these drugs. This review explores the mechanism by which DPP-4 inhibitors may increase the risk of heart failure and possible differences among these drugs. The available research suggests that DPP-4 inhibitors cause sympathetic activation as a class effect and this may increase the risk of heart failure. Unlike other DPP-4 inhibitors, sitagliptin and alogliptin are mainly excreted in the urine and suppress renal sodium-hydrogen exchanger 3 activity. These two drugs did not increase the risk of hospitalization for heart failure in large-scale cardiovascular outcomes studies.

Do DPP-4 Inhibitors Cause Heart Failure Events by Promoting Adrenergically Mediated Cardiotoxicity? Clues From Laboratory Models and Clinical Trials

RATIONALE

DPP-4 (dipeptidyl peptidase-4) inhibitors have increased the risk of heart failure events in both randomized clinical trials and observational studies, but the mechanisms that underlie their deleterious effect remain to be elucidated. Previous work has implicated a role of these drugs to promote cardiac fibrosis.

OBJECTIVE

This article postulates that DPP-4 inhibitors increase the risk of heart failure events by activating the sympathetic nervous system to stimulate cardiomyocyte cell death, and it crystallizes the findings from both experimental studies and clinical trials that support the hypothesis.

METHODS AND RESULTS

Inhibition of DPP-4 not only potentiates the actions of GLP-1 (glucagon-like peptide-1; which can increase myocardial cAMP) but also potentiates the actions of SDF-1 (stromal cell-derived factor 1), NPY (neuropeptide Y), and substance P to activate the sympathetic nervous system and stimulate β-adrenergic receptors to cause cardiomyocyte apoptosis, presumably through a CaMKII (Ca++/calmodulin-dependent protein kinase II) pathway. An action of SDF-1 to interfere with cAMP and protein kinase A signaling may account for the absence of a clinically overt positive chronotropic effect. This conceptual framework is supported by the apparent ability of β-blocking drugs to attenuate the increased risk of DPP-4 inhibitors in a large-scale clinical trial.

CONCLUSIONS

Sympathetic activation may explain the increased risk of heart failure produced by DPP-4 inhibitors. The proposed mechanism has major implications for clinical care because in the treatment of patients with type 2 diabetes mellitus, DPP-4 inhibitors are widely prescribed, but β-blockers are underutilized because of fears that they might mask hypoglycemia.

Self-assembling peptide nanofibers coupled with neuropeptide substance P for bone tissue engineering

The number of patients requiring flat bone transplantation continues to increase worldwide. Cell transplantation has been successfully applied clinically; however, it causes another defect site and the time requirements to harvest cells and expand them are considerable. In this study, KLD12/KLD12-SP (KLD12+KLD12-substance P [SP]) was designed to mimic endogenous tissue-healing processes. The structures of KLD12, KLD12-SP, and KLD12/KLD12-SP were observed by transmission electron microscopy and circular dichroism spectra. KLD12/KLD12-SP nanofibers (5-10 nm) were created under physiological conditions by formation of a β-sheet structure. The ability of mesenchymal stem cells (MSCs) to recruit KLD12/KLD12-SP was observed by using an in vivo fluorescence imaging system. Labeled human bone marrow stromal cells supplied via an intravenous injection were recruited to the scaffold containing KLD12/KLD12-SP. Polylactic acid/beta-tricalcium phosphate (PLA/β-TCP) scaffolds filled with KLD12/KLD12-SP were applied to repair calvarial defects. The composite constructs (groups: defect, PLA/β-TCP, PLA/β-TCP/KLD12, and PLA/β-TCP/KLD12/KLD12-SP) were implanted into rat defect sites. Bone tissue regeneration was evaluated by observing gross morphology by hematoxylin and eosin and Masson's trichrome staining at 12 and 24 weeks after surgery. Gross morphology showed that the defect site was filled with new tissue that was integrated with host tissue in the KLD12/KLD12-SP group. In addition, from the staining data, cells were recruited to the defect site and lacunae structures formed in the KLD12/KLD12-SP group. From these results, the PLA/β-TCP+KLD12/KLD12-SP composite construct was considered for enhancement of bone tissue regeneration without cell transplantation.

Substance P increases sympathetic activity during combined angiotensin-converting enzyme and dipeptidyl peptidase-4 inhibition

Dipeptidyl peptidase-4 inhibitors prevent the degradation of incretin hormones and reduce postprandial hyperglycemia in patients with type 2 diabetes mellitus. Dipeptidyl peptidase-4 degrades other peptides with a penultimate proline or alanine, including bradykinin and substance P, which are also substrates of angiotensin-converting enzyme (ACE). During ACE inhibition, substance P is inactivated primarily by dipeptidyl peptidase-4, whereas bradykinin is first inactivated by aminopeptidase P. This study tested the hypothesis that dipeptidyl peptidase-4 inhibition potentiates vasodilator and fibrinolytic responses to substance P when ACE is inhibited. Twelve healthy subjects participated in this randomized, double-blinded, placebo-controlled crossover study. On each study day, subjects received sitagliptin 200 mg by mouth or placebo. Substance P and bradykinin were infused via brachial artery before and during intra-arterial enalaprilat. Sitagliptin and enalaprilat each reduced forearm vascular resistance and increased forearm blood flow without affecting mean arterial pressure, but there was no interactive effect of the inhibitors. Enalaprilat increased bradykinin-stimulated vasodilation and tissue plasminogen activator release; sitagliptin did not affect these responses to bradykinin. The vasodilator response to substance P was unaffected by sitagliptin and enalaprilat; however, substance P increased heart rate and vascular release of norepinephrine during combined ACE and dipeptidyl peptidase-4 inhibition. In women, sitagliptin diminished tissue plasminogen activator release in response to substance P both alone and during enalaprilat. Substance P increases sympathetic activity during combined ACE and dipeptidyl peptidase-4 inhibition.

CLINICAL TRIAL REGISTRATION

- URL: http://www.clinicaltrials.gov. Unique identifier: NCT01413542.

Intrathecal substance P-saporin in the dog: distribution, safety, and spinal neurokinin-1 receptor ablation

BACKGROUND

Neurokinin-1 receptors (NK1-rs) located on superficial dorsal horn neurons are essential for integration of nociceptive input. Intrathecal injection of substance P-saporin (SP-SAP) leads to local loss of spinal NK1-r (+) neurons suggesting its potential as a therapeutic agent for chronic pain. The authors determined, in a canine model, effects of lumbar intrathecal SP-SAP.

METHODS

Distribution of SP-SAP and Saporin was determined in plasma, lumbar cerebrospinal fluid, and tissue. Safety of intrathecal SP-SAP was determined in four groups (six dogs each) administered 0 (0.9% saline), 1.5, 15, or 150 µg SP-SAP through lumbar intrathecal catheters. Behavioral, physiologic, and biochemical variables were assessed. Spinal tissues were collected at 7 and approximately 90 days, or earlier if significant morbidity developed, and analyzed for NK1-r (+) neuron loss and histopathology.

RESULTS

SP-SAP and Saporin were detectable in lumbar cerebrospinal fluid for up to 4 and 24 h, respectively. Animals receiving intrathecal saline, 1.5, or 15 µg of SP-SAP showed no persistent neurologic deficits. Three animals receiving 150 µg of SP-SAP developed pelvic limb paraparesis and were euthanized prematurely. Immunohistochemistry and in situ hybridization cell counts confirmed a significant reduction in NK1-r (+) in superficial dorsal horn neurons from lumbar spinal cord after intrathecal administration of 15 and 150 µg of SP-SAP. A significant loss of NK1-r neurons in the lumbar ventral horn occurred only with 150-µg SP-SAP.

CONCLUSION

Intrathecal 15-µg SP-SAP reduced dorsal, but not ventral, NK1-r (+) neurons at the spinal level of delivery with minimal side effects, whereas 150-µg SP-SAP resulted in motor neuron toxicity.

Wound contraction decreases with intravenously injected substance P in rabbits

Substance P is an injury-inducible endogenous factor for the mobilization of CD29+ stromal-like cells into circulation and that are major effectors of accelerated healing. In this study, we evaluated the effect of intravenously injected substance P on full-thickness skin wound healing as a secondary intention wound model. We made circular full-thickness skin wounds on the ears of 28 New Zealand white rabbits. They were treated with phosphate-buffered saline, or intravenous 5, 50, or 250 n mole/kg substance P at days 0 and 1. All substance P-treated groups showed a 2.6-5.4-fold higher CD29 expression and resulted in greatly decreased wound contraction and early maturation of the stroma. However, a significant decrease in wound contraction was measured only in the 5 n mole/kg treatment group. We conclude that intravenously injected substance P at 5 n mole/kg decreases wound contraction and promotes wound maturation in full-thickness skin wounds in a rabbit ear model.

Diagnosing postural tachycardia syndrome: comparison of tilt testing compared with standing haemodynamics

POTS (postural tachycardia syndrome) is characterized by an increased heart rate (ΔHR) of ≥30 bpm (beats/min) with symptoms related to upright posture. Active stand (STAND) and passive head-up tilt (TILT) produce different physiological responses. We hypothesized these different responses would affect the ability of individuals to achieve the POTS HR increase criterion. Patients with POTS (n=15) and healthy controls (n=15) underwent 30 min of tilt and stand testing. ΔHR values were analysed at 5 min intervals. ROC (receiver operating characteristic) analysis was performed to determine optimal cut point values of ΔHR for both tilt and stand. Tilt produced larger ΔHR than stand for all 5 min intervals from 5 min (38±3 bpm compared with 33±3 bpm; P=0.03) to 30 min (51±3 bpm compared with 38±3 bpm; P<0.001). Sn (sensitivity) of the 30 bpm criterion was similar for all tests (TILT10=93%, STAND10=87%, TILT30=100%, and STAND30=93%). Sp (specificity) of the 30 bpm criterion was less at both 10 and 30 min for tilt (TILT10=40%, TILT30=20%) than stand (STAND10=67%, STAND30=53%). The optimal ΔHR to discriminate POTS at 10 min were 38 bpm (TILT) and 29 bpm (STAND), and at 30 min were 47 bpm (TILT) and 34 bpm (STAND). Orthostatic tachycardia was greater for tilt (with lower Sp for POTS diagnosis) than stand at 10 and 30 min. The 30 bpm ΔHR criterion is not suitable for 30 min tilt. Diagnosis of POTS should consider orthostatic intolerance criteria and not be based solely on orthostatic tachycardia regardless of test used.

Cardiovascular effects of antidiabetic agents: focus on blood pressure effects of incretin-based therapies

Hyperglycemia is associated with increased risk of cardiovascular disease. Nevertheless, results of large clinical trials suggest that tight glucose control does not reduce the risk of macrovascular cardiovascular events in type 2 diabetes mellitus and may cause harm. This may reflect the adverse consequences of increased hypoglycemia or the adverse effects of many antidiabetic agents on weight gain. The consequences of intensive therapy may also depend on the mechanism of the antidiabetic agent(s) used to achieve tight control. Metformin, an antidiabetic agent that reduces weight and activates AMP-activated protein kinase, reduces risk of cardiovascular events in overweight diabetics. In contrast, the thiazolidinedione rosiglitazone increases cardiovascular risk. Sulfonylureas may increase the risk of cardiovascular events through effects on the SUR1 of the cardiac K(ATP) channel. Stable analogues of glucagon-like peptide-1 reduce body weight and blood pressure, and have favorable effects on ischemia following reperfusion in animal models. The dipeptidyl peptidase IV inhibitors prevent the breakdown of glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide, but also decrease the degradation of several vasoactive peptides. Dipeptidyl peptidase IV inhibitors have favorable effects in animal models of ischemia/reperfusion. They have been reported both to decrease and to increase blood pressure. Clinical trials will address the effect of the incretin-based agents on macrovascular cardiovascular events.

Diabetic neuropathy and heart failure: role of neuropeptides

Cardiovascular autonomic neuropathy (CAN), in which patients present with damage of autonomic nerve fibres, is one of the most common complications of diabetes. CAN leads to abnormalities in heart rate and vascular dynamics, which are features of diabetic heart failure. Dysregulated neurohormonal activation, an outcome of diabetic neuropathy, has a significant pathophysiological role in diabetes-associated cardiovascular disease. Key players in neurohormonal activation include cardioprotective neuropeptides and their receptors, such as substance P (SP), neuropeptide Y (NPY), calcitonin-gene-related peptide (CGRP), atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). These neuropeptides are released from the peripheral or autonomic nervous system and have vasoactive properties. They are further implicated in cardiomyocyte hypertrophy, calcium homeostasis, ischaemia-induced angiogenesis, protein kinase C signalling and the renin-angiotensin-aldosterone system. Therefore, dysregulation of the expression of neuropeptides or activation of the neuropeptide signalling pathways can negatively affect cardiac homeostasis. Targeting neuropeptides and their signalling pathways might thus serve as new therapeutic interventions in the treatment of heart failure associated with diabetes. This review discusses how neuropeptide dysregulation in diabetes might affect cardiac functions that contribute to the development of heart failure.

Parasympathetic and substance P-immunoreactive nerve denervation in atrial fibrillation models

BACKGROUND

Recent studies demonstrated that atrial fibrillation (AF) induced heterogeneous sympathetic hyperinnervation and baroreflex impartation, but the changes of vagal and afferent nerve are not clear.

METHODS

Six dogs underwent atrial pacing at 600 beats/min (AF group). All paced dogs developed sustained AF by 5 weeks of pacing. Tissues from six healthy dogs were used as controls. Immunohistochemistry staining of cardiac nerves was performed using anti-growth-associated protein 43 (anti-GAP43), anti-tyrosine hydroxylase, antiacetylcholine (anti-ACh), and anti-substance P (anti-SP) antibodies.

RESULTS

In AF group, the density of GAP43-positive in the right atrium (RA), atrial septum (AS), and left atrium (LA) was 5590.24±1417.51, 8083.22±1271.39, and 10854.56±1877.56 μm(2)/mm(2), respectively, which was significantly (P<.01) higher than the control group. Most of the newly sprouting nerves are sympathetic nerve. Sympathetic nerve density in AF group was significantly higher than that of control group (P<.001). Whereas denervation of parasympathetic and SP-immunoreactive nerve occurred in AF group. In the dogs with AF, the density of ACh-positive nerve in the RA, AS, and LA was 506.04±104.44, 317.72±84.10, and 114.9±29. 62 μm(2)/mm(2), respectively, which was lower than the control group (P<.01). At the same time, the density of SP-positive nerve in the atria of AF dogs was also significantly lower than the control tissues (P<.01).

CONCLUSION

AF led to significant nerve sprouting and sympathetic hyperinnervation in the canine models, but the newly sprouting nerve did not include parasympathetic and SP-immunoreactive nerve. Heterogeneous parasympathetic and SP-immunoreactive nerve denervation occurred in the AF dogs.

Interactive hemodynamic effects of dipeptidyl peptidase-IV inhibition and angiotensin-converting enzyme inhibition in humans

Dipeptidyl peptidase-IV inhibitors improve glucose homeostasis in type 2 diabetics by inhibiting degradation of the incretin hormones. Dipeptidyl peptidase-IV inhibition also prevents the breakdown of the vasoconstrictor neuropeptide Y and, when angiotensin-converting enzyme (ACE) is inhibited, substance P. This study tested the hypothesis that dipeptidyl peptidase-IV inhibition would enhance the blood pressure response to acute ACE inhibition. Subjects with the metabolic syndrome were treated with 0 mg of enalapril (n=9), 5 mg of enalapril (n=8), or 10 mg enalapril (n=7) after treatment with sitagliptin (100 mg/day for 5 days and matching placebo for 5 days) in a randomized, cross-over fashion. Sitagliptin decreased serum dipeptidyl peptidase-IV activity (13.08±1.45 versus 30.28±1.76 nmol/mL/min during placebo; P≤0.001) and fasting blood glucose. Enalapril decreased ACE activity in a dose-dependent manner (P<0.001). Sitagliptin lowered blood pressure during enalapril (0 mg; P=0.02) and augmented the hypotensive response to 5 mg of enalapril (P=0.05). In contrast, sitagliptin attenuated the hypotensive response to 10 mg of enalapril (P=0.02). During sitagliptin, but not during placebo, 10 mg of enalapril significantly increased heart rate and plasma norepinephrine concentrations. There was no effect of 0 or 5 mg of enalapril on heart rate or norepinephrine after treatment with either sitagliptin or placebo. Sitagliptin enhanced the dose-dependent effect of enalapril on renal blood flow. In summary, sitagliptin lowers blood pressure during placebo or submaximal ACE inhibition; sitagliptin activates the sympathetic nervous system to diminish hypotension when ACE is maximally inhibited. This study provides the first evidence for an interactive hemodynamic effect of dipeptidyl peptidase-IV and ACE inhibition in humans.

Evidence for the pathophysiological relevance of TRPA1 receptors in the cardiovascular system in vivo

AIMS

The aim of the study is to investigate transient receptor potential ankyrin 1 (TRPA1)-induced responses in the vasculature and on blood pressure and heart rate (HR), in response to TRPA1 agonists using wild-type (WT) and TRPA1 knockout (KO) mice.

METHODS AND RESULTS

TRPA1 agonists allyl isothiocyanate and cinnamaldehyde (CA) significantly increased blood flow in the skin of anaesthetized WT, but not in TRPA1 KO mice. CA also induced TRPA1-dependent relaxation of mesenteric arteries. Intravenously injected CA induced a transient hypotensive response accompanied by decreased HR that was, depending on genotype and dose, followed by a more sustained dose-dependent pressor response (10-320 micromol/kg). CA (80 micromol/kg) induced a depressor response that was significantly less in TRPA1 KO mice, with minimal pressor effects. The pressor response of a higher CA dose (320 micromol/kg) was observed in WT but not in TRPA1 KO mice, indicating involvement of TRPA1. Experiments using TRP vanilloid 1 (TRPV1) KO and calcitonin gene-related peptide (CGRP) KO mice provided little evidence for the involvement of TRPV1 or CGRP, nor did blocking substance P receptors affect responses. However, the cholinergic antagonist atropine sulphate (5 mg/kg) significantly inhibited the depressor response and slowed HR with CA (80 micromol/kg), but had no effect on pressor responses. The pressor response remained unaffected, even in the presence of the ganglion blocker hexamethonium bromide (1 mg/kg). The alpha-adrenergic blocker prazosin hydrochloride (1 mg/kg) significantly inhibited both components, but not slowed HR.

CONCLUSION

TRPA1 is involved in mediating vasodilation. TRPA1 can also influence changes in blood pressure of possible relevance to autonomic system reflexes and potentially to vasovagal/neurocardiogenic syncope disorders.

Sensory-nerve-derived neuropeptides: possible therapeutic targets

This review examines our developing understanding of the families and activities of some of the best known sensory-nerve-derived inflammatory neuropeptides, namely substance P, calcitonin gene-related peptide and galanin. Evidence to date shows involvement of these transmitters in a wide range of systems that includes roles as inflammatory modulators. There is an increasing understanding of the mechanisms involved in the release of the peptides from sensory nerves and these are key in understanding the potential of neuropeptides in modulating inflammatory responses and may also provide novel targets for anti-inflammatory therapy. The neuropeptides released act via specific G protein coupled receptors, most of which have now been cloned. There is knowledge of selective agonists and antagonists for many subtypes within these families. The study of neuropeptides in animal models has additionally revealed pathophysiological roles that in turn have led to the development of new drugs, based on selective receptor antagonism.