Biomedical subjects

Andrew D Grant

Publications and source records attributed to Andrew D Grant.

8 recordsLinked to original sources

PubMed2006

Protease-activated receptor 2 sensitizes the transient receptor potential vanilloid 4 ion channel to cause mechanical hyperalgesia in mice.

Exacerbated sensitivity to mechanical stimuli that are normally innocuous or mildly painful (mechanical allodynia and hyperalgesia) occurs during inflammation and underlies painful diseases. Proteases that are generated during inflammation and disease cleave protease-activated receptor 2 (PAR2) on afferent nerves to cause mechanical hyperalgesia in the skin and intestine by unknown mechanisms. We hypothesized that PAR2-mediated mechanical hyperalgesia requires sensitization of the ion channel transient receptor potential vanilloid 4 (TRPV4). Immunoreactive TRPV4 was coexpressed by rat dorsal root ganglia (DRG) neurons with PAR2, substance P (SP) and calcitonin gene-related peptide (CGRP), mediators of pain transmission. In PAR2-expressing cell lines that either naturally expressed TRPV4 (bronchial epithelial cells) or that were transfected to express TRPV4 (HEK cells), pretreatment with a PAR2 agonist enhanced Ca2+ and current responses to the TRPV4 agonists phorbol ester 4alpha-phorbol 12,13-didecanoate (4alphaPDD) and hypotonic solutions. PAR2-agonist similarly sensitized TRPV4 Ca2+ signals and currents in DRG neurons. Antagonists of phospholipase Cbeta and protein kinases A, C and D inhibited PAR2-induced sensitization of TRPV4 Ca2+ signals and currents. 4alphaPDD and hypotonic solutions stimulated SP and CGRP release from dorsal horn of rat spinal cord, and pretreatment with PAR2 agonist sensitized TRPV4-dependent peptide release. Intraplantar injection of PAR2 agonist caused mechanical hyperalgesia in mice and sensitized pain responses to the TRPV4 agonists 4alphaPDD and hypotonic solutions. Deletion of TRPV4 prevented PAR2 agonist-induced mechanical hyperalgesia and sensitization. This novel mechanism, by which PAR2 activates a second messenger to sensitize TRPV4-dependent release of nociceptive peptides and induce mechanical hyperalgesia, may underlie inflammatory hyperalgesia in diseases where proteases are activated and released.

Animals↗

PubMed2005

Evidence for a novel protective role of the vanilloid TRPV1 receptor in a cutaneous contact allergic dermatitis model.

The purpose of this study was to examine the involvement of the transient receptor potential vanilloid receptor 1 (TRPV1) in inflammatory processes observed in murine allergic contact dermatitis (ACD). Oxazolone-induced ACD evoked a significant ear swelling after 24-72 h. It was augmented in TRPV1 knockout mice at all time points and supported by histological analysis and measure of TNF-alpha. However, tissue swelling and cytokine generation was significantly reduced in both neurokinin 1 receptor and calcitonin gene-related peptide (CGRP) knockout mice. A protective involvement of the TRPV1 receptor was identified of contact dermatitis distinct from mechanisms involving the major pro-inflammatory neuropeptides.

Adjuvants, Immunologic↗

PubMed2005

An examination of neurogenic mechanisms involved in mustard oil-induced inflammation in the mouse.

The mechanisms by which topical mustard oil causes vasodilatation in the mouse were investigated using the tachykinin NK1 receptor antagonist SR140333 and the calcitonin gene-related peptide (CGRP) antagonist BIBN4096BS, alongside alphaCGRP or NK1 receptor knockout mice. Blood flow was assessed by laser Doppler flowmetry and plasma extravasation by 125I-albumin accumulation. Mustard oil produced significant plasma extravasation and vasodilatation in wild type mice, although the plasma extravasation was less than that seen with capsaicin whilst the vasodilatation was greater. The plasma extravasation was abolished in tachykinin NK1 knockout mice, whilst the vasodilatation was enhanced. BIBN4096BS was unable to inhibit the vasodilatation in wild type mice but abolished it in the NK1 knockout mice. In alphaCGRP knockout mice, mustard oil also caused plasma extravasation and vasodilatation, which were both inhibited by treatment with SR140333. These data suggest that both a tachykinin NK1 receptor agonist and a CGRP agonist are active as vasodilators, producing redundancy, requiring blockade of both mediators to prevent vasodilatation.

Animals↗

PubMed2004

Tachykinins regulate the function of platelets.

Evidence has been mounting for peripheral functions for tachykinins, a family of neuropeptides including substance P (SP), neurokinin A, and neurokinin B, which are recognized for their roles in the central and peripheral nervous system. The recent discovery of 4 new members of this family, the endokinins (EKA, B, C, and D), which are distributed peripherally, adds support to the notion that tachykinins have physiologic/endocrine roles in the periphery. In the present study we report a fundamental new function for tachykinins in the regulation of platelet function. We show that SP stimulates platelet aggregation, and underlying this is the intracellular mobilization of calcium and degranulation. We demonstrate the presence of the tachykinin receptors NK1 and NK3 in platelets and present evidence for the involvement of NK1 in SP-mediated platelet aggregation. Platelets were found to contain SP-like immunoreactivity that is secreted upon activation implicating SP-like substances in the autocrine/paracrine regulation of these cells. Indeed, NK1-blocking antibodies inhibited aggregation in response to other agonists. Of particular note is the observation that EKA/B cross-react in the SP immunoassay and are also able to stimulate platelet activation. Together our data implicate tachykinins, specifically SP and EKA/B, in the regulation of platelet function.

Blood Platelets↗

PubMed2004

Vascular actions of calcitonin gene-related peptide and adrenomedullin.

This review summarizes the receptor-mediated vascular activities of calcitonin gene-related peptide (CGRP) and the structurally related peptide adrenomedullin (AM). CGRP is a 37-amino acid neuropeptide, primarily released from sensory nerves, whilst AM is produced by stimulated vascular cells, and amylin is secreted from the pancreas. They share vasodilator activity, albeit to varying extents depending on species and tissue. In particular, CGRP has potent activity in the cerebral circulation, which is possibly relevant to the pathology of migraine, whilst vascular sources of AM contribute to dysfunction in cardiovascular disease. Both peptides exhibit potent activity in microvascular beds. All three peptides can act on a family of CGRP receptors that consist of calcitonin receptor-like receptor (CL) linked to one of three receptor activity-modifying proteins (RAMPs) that are essential for functional activity. The association of CL with RAMP1 produces a CGRP receptor, with RAMP2 an AM receptor and with RAMP3 a CGRP/AM receptor. Evidence for the selective activity of the first nonpeptide CGRP antagonist BIBN4096BS for the CGRP receptor is presented. The cardiovascular activity of these peptides in a range of species and in human clinical conditions is detailed, and potential therapeutic applications based on use of antagonists and gene targeting of agonists are discussed.

Adrenomedullin↗

PubMed2003

Basal and activity-induced release of substance P from primary afferent fibres in NK1 receptor knockout mice: evidence for negative feedback.

The concept that NK1 receptors are located pre-junctionally on substance P (SP)-containing nerves, acting as autoreceptors to inhibit SP release, has been suggested, but remains a controversial issue. To further investigate the existence of this receptor on central and peripheral terminals of primary afferent fibres, NK1 receptor knockout mice and an NK1 receptor antagonist were used in nerve-attached tissue preparations. These were the isolated dorsal horn of the spinal cord with dorsal roots attached, and the hairy skin of the hind paw with attached saphenous nerve. The results reveal that in the dorsal horn preparation, basal release of SP is significantly higher in NK1(-/-) mice than NK1(+/+) mice (P<0.05, n=7 mice/strain). However, a difference in SP release evoked in the dorsal horn by electrical stimulation of the dorsal roots or capsaicin application was not observed. In contrast, antidromic electrical stimulation of the saphenous nerve caused a substantially greater release of SP in the skin of NK1(-/-) mice than in NK1(+/+) mice (P<0.05, n=5 to 6 mice/strain). These results provide evidence for the existence of NK1 autoreceptors on sensory nerves in skin, which may be relevant to the modulation of their peripheral pathophysiological effector functions.

Afferent Pathways↗

PubMed2002

Neurokinin B induces oedema formation in mouse lung via tachykinin receptor-independent mechanisms.

The tachykinin neurokinin B (NKB) has been implicated in the hypertension that characterises pre-eclampsia, a condition where tissue oedema is also observed. The ability of NKB, administered intradermally or intravenously, to induce oedema formation (assessed as plasma extravasation) was examined by extravascular accumulation of intravenously injected (125)I-albumin in wild-type and tachykinin NK(1) receptor knockout mice. Intradermal NKB (30-300 pmol) caused dose-dependent plasma extravasation in wild-type (P < 0.05) but not NK(1) knockout mice, indicating an essential role for the NK(1) receptor in mediating NKB-induced skin oedema. Intravenous administration of NKB to wild-type mice produced plasma extravasation in skin, uterus, liver (P < 0.05) and particularly in the lung (P < 0.01). Surprisingly, the same doses of NKB led to plasma extravasation in the lung and liver of NK(1) knockout mice. By comparison, the tachykinin substance P induced only minimal plasma extravasation in the lungs of wild-type mice. The plasma extravasation produced by NKB in the lungs of NK(1) receptor knockout mice was unaffected by treatment with the NK(2) receptor antagonist SR48968 (3 mg kg(-1)), by the NK(3) receptor antagonists SR142801 (3 mg kg(-1)) and SB-222200 (5 mg kg(-1)) or by the cyclo-oxygenase (COX) inhibitor indomethacin (20 mg kg(-1)). L-Nitro-arginine methyl ester (15 mg kg(-1)), an inhibitor of endothelial nitric oxide synthase (eNOS), produced only a partial inhibition. We conclude that NKB is a potent stimulator of plasma extravasation through two distinct pathways: via activation of NK(1) receptors, and via a novel neurokinin receptor-independent pathway specific to NKB that operates in the mouse lung. These findings are in keeping with a role for NKB in mediating plasma extravasation in diseases such as pre-eclampsia.

Animals↗

PubMed2002

Evidence of a role for NK1 and CGRP receptors in mediating neurogenic vasodilatation in the mouse ear.

The aims of this study were to develop a technique to measure blood flow in the mouse ear and to investigate the nature of the vasodilator mediator(s) involved in the response to capsaicin. The response to capsaicin, applied topically, was investigated in anaesthetized CD1 or Sv129+C57BL/6 wild-type (+/+) or NK(1) receptor knockout mice (-/-). Blood flow was assessed by laser Doppler flowmetry and oedema formation by (125)I-albumin accumulation. Capsaicin induced significant increases in blood flow (0.2 - 200 microg in 20 microl) and oedema (2 - 200 microg in 20 microl). The oedema response was absent in NK(1)-/- mice and NK(1)+/+mice treated with the selective NK(1) receptor antagonist SR140333 (480 nmol kg(-1)) as expected. Furthermore, the capsaicin-evoked increase in blood flow was significantly potentiated in the knockout mice (203% of wild-type response, P<0.05) and wild-type mice treated with SR140333 (201%, P<0.05). The CGRP receptor antagonist CGRP(8 - 37) (400 nmol kg(-1)) had no effect on capsaicin-induced blood flow in NK(1)+/+mice but abolished the increased blood flow to capsaicin in NK(1)-/-, and NK(1)+/+wild-type mice pre-treated with SR140333. The results indicate that neurogenic vasodilatation can be measured in the mouse ear. The capsaicin-induced increased blood flow involves activation of, and possible interactions between, both NK(1) and CGRP(1) receptors.

Animals↗