Biomedical subjects

S D Brain

Publications and source records attributed to S D Brain.

At least 55 records · Page 3Linked to original sources

PubMed1997

A study of neurokinins and other oedema-inducing mediators and mechanisms in thermal injury.

1. Mechanisms involved in the plasma extravasation observed following thermal injury of rat dorsal skin were investigated. 2. Heat applied to the dorsal skin of anaesthetized rats by a temperature-controlled skin heater (1 cm diameter) for 5 min induced temperature-dependent plasma protein extravasation at 48-48.5 degrees C, measured for up to 4 h following initiation of heat. 3. A tachykinin NK1 receptor antagonist (SR140333), a bradykinin B2 receptor antagonist (HOE 140) and a cyclo-oxygenase inhibitor (indomethacin), when given as cotreatments prior to the selected measurement period, markedly suppressed oedema formation observed over 0-1 h (P < 0.05) but not that observed over 3-4 h after injury. 4. These results indicate that although neurokinins, bradykinin and cyclo-oxygenase products may be important for the early response to thermal injury, they do not appear to play an important role in the ongoing oedema response. 5. Neutrophils accumulate at the inflammatory site by 4 h after thermal injury. Therefore, the effect of depletion of circulating neutrophils by a rat anti-neutrophil antiserum on oedema formation over the 0-4 h period was investigated. The results show that oedema formation was similar in control and anti-neutrophil-treated rats. 6. In conclusion, the data from the present study indicate that neuropeptides as well as other vasoactive mediators play a role in the acute plasma extravasation observed after thermal injury, but not in the ongoing inflammatory injury. Neutrophils, despite their presence at sites of thermal injury, do not appear to be involved in mediating the oedema formation observed up to 4 h after thermal injury.

Animals↗

PubMed1997

Peroxynitrite: a mediator of increased microvascular permeability?

1. Increased expression of inducible nitric oxide synthase (iNOS) and subsequent elevation of nitric oxide (NO) levels at inflammatory sites have led to the suggestion that peroxynitrite (the reaction product of superoxide and NO) is involved in pro-inflammatory processes. The present study has investigated the ability of peroxynitrite to induce oedema formation in the rat cutaneous microvasculature. 2. Peroxynitrite was synthesized from hydrogen peroxide and acidified nitrite. Spectrophotometry was used to measure the concentration and breakdown of peroxynitrite. It was also used to determine maximum amounts of hydrogen peroxide and sodium nitrite remaining after synthesis. 3. Oedema formation in response to intradermally (i.d.) injected peroxynitrite, hydrogen peroxide and sodium nitrite was measured by the extravascular accumulation of i.v. [125I]-albumin in the anaesthetized rat. 4. Peroxynitrite (40, 100 and 200 nmol/site) acted in a dose-dependent manner to cause a mean (+/- SEM) increase in plasma extravasation of 24 +/- 2, 55 +/- 5 and 69 +/- 6 microL, respectively (n = 4), with resulting inflammatory oedema. Peroxynitrite induced significantly larger plasma extravasation than equivalent vehicle controls at doses of 100 (P > 0.05) and 200 nmol (P > 0.001). This increased extravasation appears to be a direct microvascular response to peroxynitrite administration and not due to either a raised pH, necessary to stabilize the peroxynitrite, or contaminating concentrations of hydrogen peroxide or sodium nitrite from which peroxynitrite is formed. 5. These results suggest that peroxynitrite acts to increase microvascular permeability and oedema formation. Therefore, peroxynitrite may mediate vascular pro-inflammatory effects in addition to its direct cytotoxic activity.

Animals↗

PubMed1996

Investigation of 6-hydroxydopamine-induced plasma extravasation in rat skin.

Perfusion of 6-hydroxydopamine into the rat knee and trachea induces plasma extravasation, possibly by tissue-specific mechanisms involving sympathetic and sensory nerves respectively, and we aimed to identify the mediators which contribute to this response in skin. 6-Hydroxydopamine (both hydrobromide and hydrochloride salts), dose dependently increased plasma extravasation into rat dorsal skin, however, when compared to bradykinin or the tachykinin NK1 receptor agonist GR73632, high concentrations of 6-hydroxydopamine (1-10 mumol/site) were required. The response to 6-hydroxydopamine was not inhibited in chemically sympathectomised rats (6-hydroxydopamine, 300 mg/kg i.p. over 7 days) but was significantly reduced by co-administration with the histamine (H1) and the 5-HT receptor antagonists mepyramine and methysergide and in skin sites pre-injected with compound 48/80 (4 micrograms, -18 h) to degranulate dermal mast cells. The response was not inhibited by co-injection of the tachykinin NK1 receptor antagonist SRI40333 or by the cyclo-oxygenase inhibitor indomethacin (5 mg kg-1 i.p., -30 min) except at the lowest dose of 6-hydroxydopamine (1 mumol/site). We conclude that 6-hydroxydopamine is not a potent or selective mediator of increased vascular permeability in rat skin but, at high concentrations, may induce oedema formation via release of vasoactive amines from mast cells, augmented by generation of prostaglandins.

Animals↗

PubMed1996

The effect of Phoneutria nigriventer (armed spider) venom on arterial blood pressure of anaesthetised rats.

The changes induced in the mean arterial blood pressure of anaesthetised rats following the administration of armed spider (Phoneutria nigriventer) venom have been investigated. The intravenous injection of Phoneutria nigriventer venom (0.1 mg/kg) evoked a brief and reversible decrease in the mean arterial blood pressure whereas a higher dose of venom (0.3 mg/kg) caused a biphasic response characterized by a short-lasting hypotension followed by a sustained and prolonged hypertension (40-50 min). These changes were accompanied by tachycardia, salivation, fasciculations, defecation and respiratory disturbances. Pretreatment of the animals with atropine (10 mg/kg), propranolol (100 mg/kg), phenoxybenzamine (100 mg/kg) and indomethacin (4 mg/kg) did not significantly affect the mean arterial blood pressure changes induced by Phoneutria nigriventer venom. Similarly, the bradykinin B2 receptor antagonist Hoe 140 (D-Arg-[Hyp3,Thi5,DTic7,Oic8]-bradykinin) (0.6 mg/kg), the PAF receptor antagonist WEB 2086 (3-(4-(2-chlorophenyl)-9-methyl-6H-thieno-(3,2f) (1,2,4)-triazolo-(4,3-a) (1,4)-diazepine-2-yl)-(4-morpholinyl)-1-propanone) (20 mg/kg), the tachykinin NK1 receptor antagonist SR 140333 ((S)1-(2-[3-(3,4-dichlorophenyl)-1-(3-iso-propoxyphenyl acetyl) piperidin-3-yl] ethyl)-4-phenyl-1-azoniabicyclo[2.2.2] octane, chloride) (0.5 mg/kg), the tachykinin NK2 receptor antagonist SR 48968 ((S)-N-methyl-N[4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophen yl) butyl]benzamide) (0.5 mg/kg) and the nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester (10 mg/kg) had no significant effect on the mean arterial blood pressure changes induced by Phoneutria nigriventer venom. The increase in the blood pressure induced by Phoneutria nigriventer venom was also not significantly affected by either the angiotensin II receptor antagonist losartan (10 mg/kg) or the endothelin ETA receptor antagonist FR 139317 ((R)2-[(R)-2-[[1-(hexahydro-1H-azepinyl]carbonyl]amino-4-methyl- pentanoyl]amino-3-[3-(1-methyl-1H-indoyl)]propionyl] amino-3-(2-pyridyl) propionic acid) (30 mg/kg). The ATP-dependent K+ channel antagonist glibenclamide (50 mg/kg) reduced by 40% the hypotension induced by Phoneutria nigriventer venom without affecting the hypertensive response. Pretreatment of the animals with L-type Ca2+ channel antagonists such as verapamil (10-100 micrograms/kg/min), diltiazem (40-120 micrograms/kg/min) and nifedipine (0.3-10 mg/kg) markedly attenuated the hypertension induced by Phoneutria nigriventer venom. Verapamil (30 micrograms/kg/min) and diltiazem (120 micrograms/kg/min) also promptly reversed the established hypertension induced by Phoneutria nigriventer venom when infused 8 min after venom injection. Our results indicate that the brief decrease of blood pressure induced by Phoneutria nigriventer venom is partially due to ATP-dependent K+ channel activation. The prolonged hypertension seems to result from direct Ca2+ entry into vascular and/or cardiac muscles.

Acetylcholine↗

PubMed1996

Calcitonin gene-related peptide: vasoactive effects and potential therapeutic role.

1. The cardiovascular biology of calcitonin gene-related peptide (CGRP) and the structurally related peptides amylin and adrenomedullin are briefly reviewed. 2. CGRP is a potent and long-lasting vasodilator; its possible role in disease, and the therapeutic potential of CGRP receptor agonists and antagonists is discussed.

Amino Acid Sequence↗

PubMed1996

The effect of intra-articular capsaicin on nerve fibres within the synovium of the rat knee joint.

The aim of this study was to establish the effects of intra-articular capsaicin (pelargonic acid vallinylamide) on synovial innervation of the rat knee. Rats were sacrificed 1, 2, 4 and 7 days after intra-articular injection of capsaicin and joint tissues stained with either conventional haematoxylin and eosin (H and E) or with specific antibodies to the calcitonin gene-related peptide (CGRP), substance P (both of which are markers for primary afferent fibres), the C-flanking peptide of neuropeptide Y (CPON) (localised in postganglionic sympathetic fibres), or protein gene product 9.5 (a pan-neuronal marker). At lower concentrations (0.1% and 0.25%), capsaicin produced no change in peptide staining pattern or histological appearance. At 0.5% capsaicin, there was complete loss of nerve fibres showing positive staining for CGRP and substance P at all time points. Staining for CPON and protein gene product 9.5 was still present, but decreased, 1 and 2 days after treatment and virtually absent at 4 and 7 days. These findings provide evidence for partially selective denervation induced by 0.5% capsaicin, in contrast to 1% capsaicin which abolished staining for all peptide markers, indicating a total ablation of nerve fibres. A consistent but unexpected finding was the presence of a severe inflammatory response in joints treated with 0.5% and 1% capsaicin. An influx of polymorphonuclear leucocytes was found to occur within 4 h of injection, with progressive appearance of mononuclear cells after this time. We conclude that it is difficult to specifically deplete sensory nerve fibres from the synovium by means of local capsaicin injection. Although selective loss of staining for sensory nerve fibres could be achieved by injection of 0.5% capsaicin, there was progressive non-specific loss of post-ganglionic autonomic fibres which may be related to the severe inflammatory response provoked by the higher doses of capsaicin.

Animals↗

PubMed1996

The effect of a tachykinin NK1 receptor antagonist, SR140333, on oedema formation induced in rat skin by venom from the Phoneutria nigriventer spider.

1. The possibility that tachykinin NK1 receptors are involved in the plasma extravasation evoked by intradermal (i.d.) injection of Phoneutria nigriventer venom (PNV) in rat dorsal skin in vivo has been investigated. 2. Local oedema formation induced by the i.d. injection of test agents was measured by the extravascular accumulation of intravenously (i.v.) injected 125I-labelled human serum albumin over a 30 min period. 3. The tachykinin NK1 agonist, GR73632 (30 pmol per site), induced local oedema formation which was potentiated by co-injection with the neuropeptide vasodilator, calcitonin gene-related peptide (CGRP, 10 pmol per site). The non-peptide tachykinin NK1 receptor antagonist, SR140333 (0.03-1 nmol per site co-injected, i.d.) significantly inhibited (0.3 nmol per site, P < 0.05; 1 nmol per site, P < 0.001) local oedema formation induced by GR73632 with CGRP but not that induced by histamine (10 nmol per site) with CGRP. 4. PNV (0.03-0.3 microgram per site) injected i.d. induced dose-dependent local oedema formation. SR140333 (1 nmol per site, co-injected i.d.) inhibited oedema formation; with complete inhibition observed at doses of 0.03 microgram (P < 0.05) and 0.1 microgram (P < 0.001); and partial inhibition (50%) observed with the highest dose of PNV, 0.3 microgram (P < 0.05). 5. Local oedema formation induced by PNV was not affected by systemic pretreatment with the bradykinin B2 receptor antagonist, Hoe 140 (80 nmol kg-1, i.v.), which was used at a dose which significantly inhibited oedema formation by bradykinin (1 nmol per site). 6. Local oedema formation induced by PNV was significantly inhibited (P < 0.01) by co-injection of the histamine H1 receptor antagonist, mepyramine (2.5 nmol per site), together with the 5-hydroxytryptamine (5-HT) antagonist, methysergide (2.8 nmol per site). 7. In the presence of all three antagonists (mepyramine 2.5 nmol per site; methysergide, 2.8 nmol per site and SR140333 1 nmol per site), the plasma extravasation induced by PNV was further significantly inhibited (P < 0.001, when compared with PNV injected i.d. alone; P < 0.05 when compared with PNV co-injected with mepyramine and methysergide and P < 0.01, when compared with PNV co-injected with SR140333). 8. These results suggest that oedema formation evoked by i.d. PNV in rat skin may be partially mediated via a mechanism involving tachykinin NK1 receptors and that this effect is independent of histamine and 5-HT.

Animals↗

PubMed1996

Involvement of sensory neuropeptides in the development of plasma extravasation in rat dorsal skin following thermal injury.

1. The involvement of the neuropeptides, substance P (SP) and calcitonin gene-related peptide (CGRP) in plasma extravasation following thermal injury of rat dorsal skin was investigated. 2. Heat applied to the dorsal skin of anaesthetized rats by a temperature-controlled skin heater (1 cm diameter) for 5 min induced temperature-dependent plasma protein extravasation at 46 degrees C to 50 degrees C measured over the 20 min following initiation of heat. 3. The NK1-receptor antagonist, SR140333, at doses above 36 nmol kg-1, significantly (P < 0.05) inhibited plasma extravasation by up to 79 +/- 3% (120 nmol kg-1) after heat application at 48 degrees C and by up to 53 +/- 10% (120 nmol kg-1) after heat application at 50 degrees C. 4. The CGRP1-receptor antagonist, CGRP8-37, at doses of 200 and 400 nmol kg-1, significantly inhibited (P < 0.01) plasma extravasation by 55 +/- 9 and 60 +/- 12%, respectively, after heat application at 48 degrees C. At a dose of 200 nmol kg-1 CGRP8-37 inhibited plasma extravasation by 41 +/- 8% after heat application at 50 degrees C. 5. SR140333, 120 nmol kg-1, and CGRP8-37, 200 nmol kg-1 together significantly (P < 0.01) inhibited plasma extravasation by 84 +/- 15% after heating at 48 degrees C for 5 min. 6. In experiments where the response was measured for 0-5, 5-10, 10-15 or 15-20 min, SR140333, 120 nmol kg-1, significantly (P < 0.05) inhibited plasma extravasation which had accumulated during all the time periods measured. In comparison, CGRP8-37, 200 nmol kg-1, was significantly (P < 0.05) effective at time-points up to 15 min after initiation of injury. 7. In longer term experiments plasma protein extravasation continued for at least 95 min after initiation of thermal injury. SR140333, at a dose of 120 nmol kg-1, significantly inhibited plasma extravasation for up to 65 min after initiation of injury. 8. In conclusion, the data from the present study demonstrate that both SP and CGRP are likely to have a role in the acute plasma extravasation after thermal injury. In addition, evidence suggests SP may have a role in plasma extravasation for up to 65 min.

Animals↗

PubMed1995

The modulation of the increase in rat facial skin blood flow observed after trigeminal ganglion stimulation.

Electrical stimulation of the trigeminal ganglion causes an increase in facial skin blood flow in the anaesthetised rat, as measured by laser Doppler flowmetry. We investigated the modulation of this neurogenic vasodilator response using selective receptor agonists for putative prejunctional inhibitory receptors, as well as other pharmacological agents to further characterise this response. [D-Ala2,Me-Phe4,Gly5-ol]enkephalin (DAGO, a mu-opioid receptor agonist) inhibited the vasodilator response in a dose-related (0.058-5.8 mumol/kg i.v.) and naloxone-sensitive manner. A similar inhibitory response was observed with the local anaesthetic lignocaine (2% w/v, s.c. 20 microliters). In contrast, the histamine H3-receptor agonist alpha-methylhistamine (15 or 35 mumol/kg, i.v.) and the 5-HT1D receptor agonists sumatriptan (0.24 or 2.4 mumol/kg, i.v.) and CP 122,288 (0.0003-3 mumol/kg, i.v.) had no effect on these responses. Similarly, atropine (1.5 mumol/kg, i.v.) and indomethacin (28 mumol/kg, i.v.) did not alter the vasodilatation observed in this model. In conclusion, only mu-opioid receptor activation and local anaesthetic had any inhibitory action on the neurogenic vasodilatation observed in this model.

Animals↗

PubMed1995

Topical glucocorticoids inhibit neurogenic inflammation: involvement of lipocortin 1.

Topical glucocorticoid treatment (betamethasone-17-valerate (0.018 mg/cm2, 3 h pretreatment) significantly inhibited neurogenic oedema formation induced by electrical antidromic stimulation (2 Hz, 15 V, 0.1 ms for 5 min) of the rat saphenous nerve; a response mediated by neuropeptides released from activated capsaicin-sensitive sensory C-fibres. Oedema formation was estimated by measurement of extravasation of i.v. injected 125I-albumin into skin. The inhibitory effect of the topical glucocorticoid was reversed by passive immunisation of rats with polyclonal antibody to the glucocorticoid-inducible anti-inflammatory protein lipocortin 1 (1 ml/kg, s.c., 24 h pretreatment) whilst a non-immune serum was without effect. Similarly the glucocorticoid receptor antagonist RU38486 (20 mg/kg, 2 and 20 h pretreatment) abrogated the response indicating specific binding to glucocorticoid receptors. Topical glucocorticoid treatment also inhibited the oedema produced by intradermal substance P (0.1 nmol) in the dorsal skin of rats. Topical glucocorticoid inhibited neurogenic oedema formation partly through a mechanism dependent upon lipocortin 1. This inhibition may be partly due to a post-junctional effect upon substance P activity/binding however a pre-junctional component cannot be excluded.

Administration, Topical↗

PubMed1995

Trigeminal ganglion stimulation increases facial skin blood flow in the rat: a major role for calcitonin gene-related peptide.

Activation of the trigeminovascular system leads to neurogenic inflammation within the dura mater and cerebral vasodilatation. These processes have been implicated in the pathogenesis of migraine headache. Neurogenic vasodilator responses to trigeminal ganglion stimulation were investigated in rat facial skin, an area innervated by the trigeminal nerve. Microvascular blood flow changes in the facial skin were measured in anaesthetised rats, using laser Doppler flowmetry. Electrical stimulation of the trigeminal ganglion caused an ipsilateral increase in facial skin blood flow which was found to be frequency dependent (0.5-10 Hz). The role of several neuropeptides in these blood flow responses was studied using selective receptor antagonists. The calcitonin gene-related peptide antagonist, CGRP8-37 (400 nmol.kg-1, i.v.) had no effect on resting levels of facial skin blood flow, but markedly inhibited responses induced by trigeminal ganglion stimulation (5 Hz, 10 V, 1 ms for 30 s). However, neither the neurokinin-1 (NK1) receptor antagonist, RP67580 (0.23 or 2.3 mumol.kg-1, i.v.) nor the vasoactive intestinal peptide (VIP) antagonist, [p-Cl-D-Phe6,Leu17]-VIP (15 or 30 nmol.kg-1, i.v.) had any effect on these responses. These results suggest that CGRP is the major neuropeptide involved in the vasodilator response to trigeminal ganglion stimulation in rat facial skin. Clarification of the mechanisms involved in this neurogenic vasodilator response may aid the development of drugs that target the trigeminovascular system during migraine headache.

Animals↗

PubMed1995

The involvement of calcitonin gene-related peptide (CGRP) and substance P in feline pial artery diameter responses evoked by capsaicin.

The effects of capsaicin and selective neuropeptide antagonists on pial artery diameter were measured using an on-line image analyser in anaesthetised cats, in order to monitor the effects of mediators released in response to activation of trigeminal nerves. Perivascular injection of CGRP (10(-8) M) and the neurokinin-1 (NK1) receptor agonist substance P methyl ester, SPOMe (10(-6) M) produced an increase in pial artery diameter. The vasodilatory action of these agonists was significantly and selectively inhibited using the CGRP receptor antagonist, CGRP8-37 (10(-6) M), and the NK1 receptor antagonist, CP99994 (10(-6) M) respectively. Capsaicin (10(-8)-10(-5) M) produced a biphasic response upon perivascular injection that was concentration dependent. At 10(-6) M capsaicin an initial transient vasoconstriction was observed followed by a longer-lasting vasodilatation. The vasodilator component was significantly reduced by CGRP8-37 (10(-6) M) or CP99994 (10(-6) M). These results show that chemical (capsaicin) activation of trigeminal nerves leads to vasodilatation of feline arteries in situ. This vasodilatation is mediated via the activation of CGRP and NK1 receptors probably via the efferent release of CGRP and a substance P-like peptide.

Anesthetics↗

PubMed1995

Mechanism of bradykinin-induced plasma extravasation in the rat knee joint.

1. We have investigated the mechanism of bradykinin (BK)-induced plasma extravasation into the knee joint of the anaesthetized rat. Accumulation of [125I]-human serum albumin within the synovial cavity was used as a marker of increased vascular permeability. 2. Perfusion with BK (1 microM) produced significant plasma extravasation into the knee which was inhibited by co-perfusion of the selective bradykinin B2 receptor antagonist D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin (Hoe 140, 200 nM). 3. The bradykinin B1 receptor agonist, [des-Arg9]-BK (up to 100 mM), did not induce plasma extravasation into the knee joint, over this time period. 4. Chemical sympathectomy by chronically administered 6-hydroxydopamine (6-OHDA) did not inhibit bradykinin-induced plasma extravasation. Acute intra-articular perfusion with 6-OHDA (to stimulate transmitter release from sympathetic nerve terminals) at concentrations up to 50 mM did not induce significant plasma extravasation. Intra-articular perfusion of 100 mM 6-OHDA induced significant plasma extravasation but produced severe systemic toxicity. 5. The selective neurokinin1 (NK1) receptor antagonist, RP67580 (230 nmol kg-1), or receptor antagonists for the mast cell products histamine and 5-hydroxytryptamine did not significantly inhibit BK-induced plasma extravasation. 6. Co-perfusion of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) (1 mM) did not significantly inhibit the response to BK. 133Xe clearance from L-NAME (1 mM)-injected joints was significantly (P < 0.05) reduced compared to D-NAME injected joints, suggesting a reduction in blood flow as a result of decreased basal NO production. Systemic administration of L-NAME at doses sufficient to produce significant and sustained elevation of blood pressure (5 or 30 mg kg-1, i.v. 15 min prior to BK perfusion) also failed to significantly inhibit the BK-induced response.7 We conclude that, in normal joints, BK induces plasma extravasation by acting on bradykinin B2 receptors and that this response is not dependent on secondary release of mediators from sympathetic nerve terminals, sensory nerves, mast cells or on generation of NO.

Adrenergic beta-Antagonists↗

PubMed1995

Evidence for ETA and ETB receptors in rat skin and an investigation of their function in the cutaneous microvasculature.

1. The relative contribution of ETA and ETB receptors in the response of rat skin to endothelins was investigated by use of the selective ETB agonist IRL-1620 and the selective ETA antagonist BQ-123. 2. Binding data suggest the presence of ETA and ETB receptors as preincubation with [Ala3,11,18Nle7]-endothelin-1 reduced ET-1 binding by approximately 40%. 3. Intradermal injection of endothelin-1 (ET-1, 1-10 pmol/site) and ET-3 (3-100 pmol/site) induced a dose-dependent decrease in local blood flow assessed by 133Xe clearance at test sites in rat skin. 4. The endothelin analogue [Ala3,11,18Nle7]-ET-1 (30-1000 pmol/site) induced significant vasoconstriction (P < 0.05) at the highest doses used and the selective ETB receptor agonist, IRL-1620 [Suc[Glu9,Ala11,15] endothelin (8-21)], (0.01-100 pmol/site) acted in a potent manner to induce a significant (P < 0.01) dose-dependent decrease in 133Xe clearance. 5. Co-injection with the selective ETA receptor antagonist, BQ-123 (1 nmol/site), completely abolished the vasoconstriction to ET-1 and partially to ET-3, but had no effect on IRL-1620-induced vasoconstriction. In addition, IRL-1620 responses were not altered at sites treated with submaximal doses of a nitric oxide synthase inhibitor or a prostaglandin synthase inhibitor. 6. ET-1 and IRL-1620 (100 fmol-1 pmol/site) did not induce oedema formation as measured by [125I]-albumin accumulation in the presence or absence of the vasodilator, calcitonin gene-related peptide (CGRP). ET-1 (1-3 pmol/site) inhibited substance P-induced oedema formation and this effect,suggested to be secondary to a vasoconstrictor effect, was significantly reversed by BQ-123 (1 nmol/site).7. The findings in this study indicate that there are ETA and ETB receptors in rat skin and agents which activate either receptor act to mediate a decrease in cutaneous blood flow, but have no effect on increased microvascular permeability.

Animals↗

PubMed1995

Effect of a 5-HT1 receptor agonist, CP-122,288, on oedema formation induced by stimulation of the rat saphenous nerve.

Neurogenic oedema formation in the rat hind paw skin induced by electrical stimulation of the saphenous nerve and measured by extravasation of [125I]-albumin, was inhibited by the 5-HT1B receptor agonist, CP-93,129, and the novel tryptamine analogue, CP-122,288. Significant inhibition of up to 66% of control was observed with CP-122,288 (2 x 10(-14) - 2 x 10(-7) mol kg-1) and CP-93,129 (5 x 10(-7) - 5 x 10(-6) mol kg-1), with the minimum effective dose for CP-122,288 being about 10(7) fold less than that for CP-93,129. Oedema formation induced by the intradermal administration of exogenous mediators (substance P and histamine) in rat dorsal skin was not inhibited by CP-122,288 (2 x 10(-10) mol kg-1). These results suggest that CP-122,288 is a potent inhibitor of neurogenic inflammation in rat skin and that the effect may be due to a prejunctional inhibition of neuropeptide release.

Analysis of Variance↗

PubMed1995

An investigation into the mechanism of capsaicin-induced oedema in rabbit skin.

1. Oedema formation induced by intradermal capsaicin has been studied in rabbit skin. The effect of the anti-inflammatory steroid dexamethasone and also of a range of known inhibitors of oedema formation have been investigated in order to elucidate mechanisms involved in capsaicin-induced oedema formation. 2. Oedema formation, in response to intradermally-injected test agents, was measured by the local extravascular accumulation of intravenously injected 125I-labelled albumin. In separate experiments skin blood flow was assessed by the clearance of intradermally-injected 133xenon. 3. Oedema formation induced by intradermal histamine (3 nmol) and bradykinin (1 nmol), when in the presence of vasodilator doses of calcitonin gene-related peptide (CGRP) (3 pmol) or prostaglandin E1, (PGE1) (10 pmol), was significantly inhibited (P < 0.01) in rabbits pretreated with intravenous dexamethasone (3 mg kg-1, -4 h). In contrast dexamethasone had no effect on capsaicin (3 mumol)-induced oedema formation or, on capsaicin (30-100 nmol)-induced blood flow. 4. Oedema formation observed in response to intradermal capsaicin (3 mumol) was significantly inhibited (P < 0.01) when the selective capsaicin antagonist, ruthenium red (3 nmol) was co-injected. This suggests that the mechanism of capsaicin-induced oedema involves activation of sensory nerves. However, oedema was not inhibited when capsaicin was co-injected with the neurokinin NK1 receptor antagonist, RP67580 (10 nmol), the NK2 antagonist SR48960 (10 nmol) or the CGRP antagonist CGRP8-37 (300 pmol). 5. Oedema formation induced by capsaicin was not inhibited when co-injected with the histamine HI receptor antagonist, mepyramine (3 nmol), the PAF antagonist, WEB 2086 (100 nmol), the bradykinin B2 receptor antagonist, Hoel4O (1 nmol), or the cyclo-oxygenase inhibitor, indomethacin (10 nmol),suggesting that these mediators do not play a major role in the capsaicin-induced response.6. Histological analysis of capsaicin-treated skin sites revealed undamaged, intact microvessels and lack of haemorrhage. Further, co-injection of capsaicin with the hydrogen peroxide remover, catalase(2,200 u), had no effect on oedema formation. This suggests that capsaicin does not induce oedema formation secondary to free radical-induced damage.7. These results indicate that capsaicin-induced oedema in rabbit skin involves activation of sensory nerves. However, the oedema is not inhibited by pretreatment with the anti-inflammatory steroid,dexamethasone. Further the mechanisms which lead to the oedema formation observed after intradermal capsaicin remain unknown.

Alprostadil↗

PubMed1995

Interaction of human adrenomedullin 13-52 with calcitonin gene-related peptide receptors in the microvasculature of the rat and hamster.

1. Adrenomedullin (ADM), a recently discovered circulating hypotensive peptide, shares limited sequence homology with the sensory nerve-derived vasodilator, calcitonin gene-related peptide (CGRP). This study compared the vasodilator effect of sequence 13-52 of human adrenomedullin (ADM13-52) with that of human alpha CGRP (CGRP), in the microvasculature of the hamster cheek pouch and rat skin in vivo. 2. Single arterioles (20-40 microns diameter) in the hamster cheek pouch were visualised by intravital microscopy and video recording, and measured by image analysis. Both ADM13-52 (1 pmol-0.4 nmol) and CGRP (0.1 pmol-1 nmol) evoked dose-related increases in the diameter of preconstricted arterioles (n = 6). ADM13-52 (ED50 14 pmol) was 20 fold less active than CGRP (ED50 0.71 pmol). The kinetics of onset and decline of vasodilator responses to both peptides were similar, with vasodilator responses to both peptides reaching a maximum at ca. 2 min, and reversing after 10-15 min (n = 5-7). The submaximal increase in blood flow evoked by ADM13-52 was significantly inhibited (P < 0.05; n = 6) by the CGRP1 receptor antagonist, CGRP8-37, at a dose (300 nmol kg-1, i.v.) that we have previously shown to inhibit significantly equivalent vasodilator responses to CGRP in this preparation. 3. In experiments measuring changes in local blood flow in rat skin by a 133xenon clearance technique, intradermal injection of both ADM13-52 (3-300 pmol) and CGRP (0.1-30 pmol) evoked dose-related increases in local blood flow. ADM13-52 (ED50 27 pmol) was 17 fold less potent than CGRP (ED501.6 pmol) (n = 6). The submaximal increase in blood flow evoked by both peptides was significantly inhibited (P<0.02; n = 5) by CGRP837 (100 nmol kg-1, i.v.).4. We conclude that ADM13-52 is a potent vasodilator in the microvasculature of the hamster and rat invivo. It mediates its vasodilator effect by arteriolar dilatation and this effect is due, at least in part, to the stimulation of CGRPI receptors.

Adrenomedullin↗

PubMed1995

Modulation of the release and activity of neuropeptides in the microcirculation.

Electrical stimulation of the sensory saphenous nerve leads to neurogenic edema formation in the innervated area of the paw of the anesthetized rat. Evidence suggests that the edema formation is the result of increased microvascular permeability mediated via neurokinin NK1 receptors and increased blood flow mediated via calcitonin gene related peptide CGRP1 receptors. Results indicate that selective receptor antagonists will only inhibit the response mediated by the specific receptor they antagonise. In the case of neurogenic inflammation, where it is common for more than one biologically active neuropeptide to be released concomitantly, it may be more sensible to develop agents that inhibit neuropeptide release. The effects of some agents suggested to affect neurogenic responses are presented. The anti-inflammatory steroid dexamethasone (1 mg/kg subcutaneously, -4 h) significantly (p < 0.01) inhibited edema formation, but the mechanism of action is likely to be related to the general anti-edema effect of dexamethasone. In contrast the anti-asthma agent nedocromil sodium (up to 10 mg/kg intravenously, -15 min) and the histamine H3 agonist (R)-alpha-methyl histamine (1-10 mg/kg intravenously, -5 min) both failed to inhibit saphenous nerve induced edema formation, despite positive results in other sensory nerve systems. The results are discussed in the context of evidence obtained using other agents in skin.

Animals↗