Effects of capsaicin, bradykinin and prostaglandin E2 in the human skin

Roles of calcitonin gene-related peptide in the skin, and other physiological and pathophysiological functions

Skin immunity is regulated by many mediator molecules. One is the neuropeptide calcitonin gene-related peptide (CGRP). CGRP has roles in regulating the function of components of the immune system including T cells, B cells, dendritic cells (DCs), endothelial cells (ECs), and mast cells (MCs).

Herein we discuss actions of CGRP in mediating inflammatory and vascular effects in various cutaneous models and disorders.

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CGRP can help to recruit immune cells through endothelium-dependent vasodilation.

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CGRP plays an important role in the pathogenesis of neurogenic inflammation.

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Functions of many components in the immune system are influenced by CGRP.

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CGRP regulates various inflammatory processes in human skin by affecting different cell-types.

Responses of spinal trigeminal neurons to noxious stimulation of paranasal cavities - a rat model of rhinosinusitis headache

BACKGROUND

The pathophysiology of headaches associated with rhinosinusitis is poorly known. Since the generation of headaches is thought to be linked to the activation of intracranial afferents, we used an animal model to characterise spinal trigeminal neurons with nociceptive input from the dura mater and paranasal sinuses.

METHODS

In isoflurane anaesthetised rats, extracellular recordings were made from neurons in the spinal trigeminal nucleus with afferent input from the exposed frontal dura mater. Dural and facial receptive fields were mapped and the paranasal cavities below the thinned nasal bone were stimulated by sequential application of synthetic interstitial fluid, 40 mM potassium chloride, 100 µM bradykinin, 1% ethanol (vehicle) and 100 µm capsaicin.

RESULTS

Twenty-five neurons with input from the frontal dura mater and responses to chemical stimulation of the paranasal cavities were identified. Some of these neurons had additional receptive fields in the parietal dura, most of them in the face. The administration of synthetic interstitial fluid, potassium chloride and ethanol was not followed by significant changes in activity, but bradykinin provoked a cluster of action potentials in 20 and capsaicin in 23 neurons.

CONCLUSION

Specific spinal trigeminal neurons with afferent input from the cranial dura mater respond to stimulation of paranasal cavities with noxious agents like bradykinin and capsaicin. This pattern of activation may be due to convergent input of trigeminal afferents that innervate dura mater and nasal cavities and project to spinal trigeminal neurons, which could explain the genesis of headaches due to disorders of paranasal sinuses.

Fight fire with fire: Neurobiology of capsaicin-induced analgesia for chronic pain

Capsaicin, the pungent ingredient in chili peppers, produces intense burning pain in humans. Capsaicin selectively activates the transient receptor potential vanilloid 1 (TRPV1), which is enriched in nociceptive primary afferents, and underpins the mechanism for capsaicin-induced burning pain. Paradoxically, capsaicin has long been used as an analgesic. The development of topical patches and injectable formulations containing capsaicin has led to application in clinical settings to treat chronic pain conditions, such as neuropathic pain and the potential to treat osteoarthritis. More detailed determination of the neurobiological mechanisms of capsaicin-induced analgesia should provide the logical rationale for capsaicin therapy and help to overcome the treatment's limitations, which include individual differences in treatment outcome and procedural discomfort. Low concentrations of capsaicin induce short-term defunctionalization of nociceptor terminals. This phenomenon is reversible within hours and, hence, likely does not account for the clinical benefit. By contrast, high concentrations of capsaicin lead to long-term defunctionalization mediated by the ablation of TRPV1-expressing afferent terminals, resulting in long-lasting analgesia persisting for several months. Recent studies have shown that capsaicin-induced Ca²⁺/calpain-mediated ablation of axonal terminals is necessary to produce long-lasting analgesia in a mouse model of neuropathic pain. In combination with calpain, axonal mitochondrial dysfunction and microtubule disorganization may also contribute to the longer-term effects of capsaicin. The analgesic effects subside over time in association with the regeneration of the ablated afferent terminals. Further determination of the neurobiological mechanisms of capsaicin-induced analgesia should lead to more efficacious non-opioidergic analgesic options with fewer adverse side effects.

Is a positive intracutaneous test induced by penicillin mediated by histamine? A cutaneous microdialysis study in penicillin-allergic patients

Background

Diagnostic workup of penicillin allergy comprises skin testing with penicillins, and patients are deemed allergic if skin test is positive. However, the literature suggests that skin test-positive patients may be challenge-negative, indicating that the skin test may be falsely positive.

Objective

To investigate real-time histamine release from a positive intracutaneous test induced by penicillin in patients with positive and negative challenges to penicillin.

Methods

Skin microdialysis was performed in 21 penicillin-allergic patients with positive skin test, 13 non-allergic volunteers serving as negative controls, and 7 grass pollen-allergic patients serving as positive controls. Histamine was measured by microdialysis after skin test with penicillin/grass/NaCl. Penicillin challenge was subsequently performed in 12 of the patients.

Results

Only 10/21 patients (47.6%) were skin test positive at microdialysis. During microdialysis 13 single intracutaneous tests were positive and histamine was detected in 4/13 occurring in four challenge positive patients. Thirteen/21 patients (61.9%) were deemed allergic to penicillin; eight had positive skin test. Two patients with positive skin test were challenge negative. In grass pollen allergic patients, 7/7 had a positive intracutaneous test to grass and all released histamine in the wheals. All 13 negative controls had negative intracutaneous test to penicillin and no histamine release.

Conclusion

Histamine was only detected in the minority of positive intracutaneous tests with penicillin in penicillin-allergic patients. Other mediators may be involved.

Influence of capsaicin infusion on secondary peristalsis in patients with gastroesophageal reflux disease

AIM

To determine whether capsaicin infusion could influence heartburn perception and secondary peristalsis in patients with gastroesophageal reflux disease (GERD).

METHODS

Secondary peristalsis was performed with slow and rapid mid-esophageal injections of air in 10 patients with GERD. In a first protocol, saline and capsaicin-containing red pepper sauce infusions were randomly performed, whereas 2 consecutive sessions of capsaicin-containing red pepper sauce infusions were performed in a second protocol. Tested solutions including 5 mL of red pepper sauce diluted with 15 mL of saline and 20 mL of 0.9% saline were infused into the mid-esophagus via the manometric catheter at a rate of 10 mL/min with a randomized and double-blind fashion. During each study protocol, perception of heartburn, threshold volumes and peristaltic parameters for secondary peristalsis were analyzed and compared between different stimuli.

RESULTS

Infusion of capsaicin significantly increased heartburn perception in patients with GERD (P < 0.001), whereas repeated capsaicin infusion significantly reduced heartburn perception (P = 0.003). Acute capsaicin infusion decreased threshold volume of secondary peristalsis (P = 0.001) and increased its frequency (P = 0.01) during rapid air injection. The prevalence of GERD patients with successive secondary peristalsis during slow air injection significantly increased after capsaicin infusion (P = 0.001). Repeated capsaicin infusion increased threshold volume of secondary peristalsis (P = 0.002) and reduced the frequency of secondary peristalsis (P = 0.02) during rapid air injection.

CONCLUSION

Acute esophageal exposure to capsaicin enhances heartburn sensation and promotes secondary peristalsis in gastroesophageal reflux disease, but repetitive capsaicin infusion reverses these effects.

Influence of repeated infusion of capsaicin-contained red pepper sauce on esophageal secondary peristalsis in humans

BACKGROUND

The transient receptor potential vanilloid 1 has been implicated as a target mediator for heartburn perception and modulation of esophageal secondary peristalsis. Our aim was to determine the effect of repeated esophageal infusion of capsaicin-contained red pepper sauce on heartburn perception and secondary peristalsis in healthy adults.

METHODS

Secondary peristalsis was performed with mid-esophageal injections of air in 15 healthy adults. Two separate protocols including esophageal infusion with saline and capsaicin-contained red pepper sauce and 2 consecutive sessions of capsaicin-contained red pepper sauce were randomly performed.

KEY RESULTS

After repeated infusion of capsaicin-contained red pepper sauce, the threshold volume to activate secondary peristalsis was significantly increased during slow (p < 0.001) and rapid air injections (p = 0.004). Acute infusion of capsaicin-contained red pepper sauce enhanced heartburn perception (p < 0.001), but the intensity of heartburn perception was significantly reduced after repeated capsaicin-contained red pepper sauce infusion (p = 0.007). Acute infusion of capsaicin-contained red pepper sauce significantly increased pressure wave amplitudes of distal esophagus during slow (p = 0.003) and rapid air injections (p = 0.01), but repeated infusion of capsaicin-contained red pepper sauce significantly decreased pressure wave amplitude of distal esophagus during slow (p = 0.0005) and rapid air injections (p = 0.003).

CONCLUSIONS & INFERENCES

Repeated esophageal infusion of capsaicin appears to attenuate heartburn perception and inhibit distension-induced secondary peristalsis in healthy adults. These results suggest capsaicin-sensitive afferents in modulating sensorimotor function of secondary peristalsis in human esophagus.

Characterisation and mechanisms of bradykinin-evoked pain in man using iontophoresis

Bradykinin (BK) is an inflammatory mediator that can evoke oedema and vasodilatation, and is a potent algogen signalling via the B1 and B2 G-protein coupled receptors. In naïve skin, BK is effective via constitutively expressed B2 receptors (B2R), while B1 receptors (B1R) are purported to be upregulated by inflammation. The aim of this investigation was to optimise BK delivery to investigate the algesic effects of BK and how these are modulated by inflammation. BK iontophoresis evoked dose- and temperature-dependent pain and neurogenic erythema, as well as thermal and mechanical hyperalgesia (P < 0.001 vs saline control). To differentiate the direct effects of BK from indirect effects mediated by histamine released from mast cells (MCs), skin was pretreated with compound 4880 to degranulate the MCs prior to BK challenge. The early phase of BK-evoked pain was reduced in degranulated skin (P < 0.001), while thermal and mechanical sensitisation, wheal, and flare were still evident. In contrast to BK, the B1R selective agonist des-Arg9-BK failed to induce pain or sensitise naïve skin. However, following skin inflammation induced by ultraviolet B irradiation, this compound produced a robust pain response. We have optimised a versatile experimental model by which BK and its analogues can be administered to human skin. We have found that there is an early phase of BK-induced pain which partly depends on the release of inflammatory mediators by MCs; however, subsequent hyperalgesia is not dependent on MC degranulation. In naïve skin, B2R signaling predominates, however, cutaneous inflammation results in enhanced B1R responses.

Povidone-iodine: an anti-oedematous agent?

Polyvinylpyrrolidone-iodine (PVP-I) is a well-known antiseptic, widely used in various preparations and concentrations in all surgical fields. It is also used as an irrigant for open wounds and in some centres for irrigating sockets after tooth extraction. One of the authors (GA) incidentally discovered an anti-oedematous effect of PVP-I after using it in low concentration as an irrigant/coolant during the surgical removal of lower third molars. A prospective randomized clinical trial was subsequently performed on 50 patients (25 control, 25 treatment group) undergoing removal of impacted lower third molars. In the treatment group a 0.5% PVP-I solution at a concentration of 0.5mg/ml (we call it as "Arakeri's iodine solution") resulted in a significant reduction in postoperative swelling compared with the control group (P<0.01). This effect of PVP-I was suspected due to its inhibitory effect on leukotriene B4 and leukocyte extravasation (chemotaxis). Further evaluation of the effects of PVP-I as an irrigant in oral and maxillofacial surgery is needed.

An insight into the sialome of Glossina morsitans morsitans

BACKGROUND

Blood feeding evolved independently in worms, arthropods and mammals. Among the adaptations to this peculiar diet, these animals developed an armament of salivary molecules that disarm their host's anti-bleeding defenses (hemostasis), inflammatory and immune reactions. Recent sialotranscriptome analyses (from the Greek sialo = saliva) of blood feeding insects and ticks have revealed that the saliva contains hundreds of polypeptides, many unique to their genus or family. Adult tsetse flies feed exclusively on vertebrate blood and are important vectors of human and animal diseases. Thus far, only limited information exists regarding the Glossina sialome, or any other fly belonging to the Hippoboscidae.

RESULTS

As part of the effort to sequence the genome of Glossina morsitans morsitans, several organ specific, high quality normalized cDNA libraries have been constructed, from which over 20,000 ESTs from an adult salivary gland library were sequenced. These ESTs have been assembled using previously described ESTs from the fat body and midgut libraries of the same fly, thus totaling 62,251 ESTs, which have been assembled into 16,743 clusters (8,506 of which had one or more EST from the salivary gland library). Coding sequences were obtained for 2,509 novel proteins, 1,792 of which had at least one EST expressed in the salivary glands. Despite library normalization, 59 transcripts were overrepresented in the salivary library indicating high levels of expression. This work presents a detailed analysis of the salivary protein families identified. Protein expression was confirmed by 2D gel electrophoresis, enzymatic digestion and mass spectrometry. Concurrently, an initial attempt to determine the immunogenic properties of selected salivary proteins was undertaken.

CONCLUSIONS

The sialome of G. m. morsitans contains over 250 proteins that are possibly associated with blood feeding. This set includes alleles of previously described gene products, reveals new evidence that several salivary proteins are multigenic and identifies at least seven new polypeptide families unique to Glossina. Most of these proteins have no known function and thus, provide a discovery platform for the identification of novel pharmacologically active compounds, innovative vector-based vaccine targets, and immunological markers of vector exposure.

Influence of intra-oesophageal capsaicin instillation on heartburn induction and oesophageal sensitivity in man

Heartburn is the most typical gastro-oesophageal reflux disease (GERD) symptom. The transient receptor potential vanilloid receptor-1 (TRPV(1)) is a candidate mediator of heartburn. Exposure of TRPV(1) to capsaicin is characterized by activation, followed by desensitization. Our aim was to investigate the effect of intra-oesophageal capsaicin instillation on oesophageal symptom perception (activation) and on sensitivity to oesophageal acid perfusion and oesophageal balloon distention (desensitization). In a first protocol (n = 10), saline or capsaicin solution were instilled in the mid-oesophagus and symptoms were rated at 5-min intervals for 60 min. In a second study (n = 10), oesophageal 0.1 N hydrochloric acid perfusion was performed 60 min after pretreatment with saline, low or high dose capsaicin. In a third study (n = 10), sensitivity to oesophageal balloon distention was determined before and at 30-min intervals up to 90 min after pretreatment with saline, low or high dose capsaicin. Areas under the curve (AUC) for symptom intensities under different conditions were calculated and compared with Kruskal-Wallis test. Oesophageal capsaicin instillation induced transient symptoms of retrosternal and epigastric burning in a dose-dependent fashion. After oesophageal capsaicin or saline instillation, there was no difference in symptom pattern and intensities induced by oesophageal acid perfusion. After oesophageal capsaicin or saline instillation, sensitivity to oesophageal balloon distention and oesophageal compliance were not significantly altered. Oesophageal instillation of the TRPV(1) receptor agonist capsaicin induces symptoms of retrosternal and epigastric burning in a dose-dependent fashion. Pretreatment with capsaicin does not desensitize the oesophagus to acid perfusion or to balloon distention.

Neuroanatomy and neurophysiology of itch

The specific pathway of "pure," histaminergic itch is traced from the mechano-insensitive nerve fibers in the skin to their central cortical projections. Neuropathic itch created at different levels of this anatomical pathway is reviewed. In this review the present author discusses damage to pruritoceptors in the skin, entrapment syndromes, damage to spinal ganglia, nerve root impingement, injury of the spinal cord, and cerebral damage in the distribution of the middle cerebral artery, capsula interna, or thalamus. Itch in inflamed skin resulting from interactions between nerve transmitters and other mediators of inflammation is described.

The effect of celecoxib on intrathecal morphine-induced pruritus in patients undergoing Caesarean section

Pruritus associated with intrathecal opioid administration is particularly common in pregnancy. Nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce the severity of this pruritus but have undesirable side effects. The recent development of drugs that can specifically inhibit the cyclooxygenase 2 isoenzyme have become an attractive alternative. This study was designed to evaluate the efficacy of such a drug (celecoxib) in reducing intrathecal opioid-induced pruritus in a randomised double-blinded study of 60 women undergoing Caesarean section. All of them received spinal anaesthesia with 3 ml of 0.5% hyperbaric bupivacaine and 0.3 mg preservative-free morphine. After delivery of the baby, they received either oral celecoxib 200 mg or placebo. Visual analogue scores for pain and pruritus were measured at 30 min, 2, 4, 8, and 24 h. There was no difference in the severity and onset of pain and pruritus between the two groups. Timing of administration, inadequate dosing and possible altered pharmacokinetics in pregnancy may explain the lack of efficacy.

Production of acute and chronic itch with histamine and contact sensitizers in the mouse and guinea pig

Itch is a major symptom of skin disease and is poorly understood, in part due to the lack of adequate small animal models. We show, using iontophoresis of histamine and capsaicin, that it is possible to induce scratching behaviour in both guinea pig and mouse. Use of iontophoresis may obviate the problems of induction of pain as well as itch when injection is used. The behavioural response to capsaicin, however, differs from that seen with histamine, raising the possibility that the use of scratch counts as a method of measuring itch severity needs to be set in the context of other responses. Naloxone partly inhibits scratching in mouse and guinea pig due to histamine. We also show that contact sensitization with 2-4 dinitrochlorobenzene (DNCB) can be used as a simple assay for chronic itch allowing study of scratching over at least a 15-h period. The characteristics of scratching (but not the time course) induced with DNCB are similar to those seen with histamine.

H1-antihistamines: inverse agonism, anti-inflammatory actions and cardiac effects

This review addresses novel concepts of histamine H1-receptor function and attempts to relate them to the anti-inflammatory effects of H1-antihistamines. Furthermore, the molecular mechanisms underlying the cardiotoxic effects of H1-antihistamines are discussed. H1-receptors are G-protein-coupled-receptors (GPCRs), the inactive and active conformations of which coexist in equilibrium. The degree receptor activation in the absence of histamine is its 'constitutive activity'. In this two-state model, histamine acts as an agonist by combining with and stabilizing the activated conformation of the H1-receptor to shift the equilibrium towards the activated state. Drugs classified previously as antagonists act as either inverse agonists or neutral antagonists. Inverse agonists combine with and stabilize the inactive conformation of the receptor to shift the equilibrium towards the inactive state. Thus, they may down-regulate constitutive receptor activity, even in the absence of histamine. Neutral antagonists combine equally with both conformations of the receptor, do not affect basal receptor activity but do interfere with agonist binding. All H1-antihistamines examined to date are inverse agonists. As the term 'H1-receptor antagonists' is obviously erroneous, we suggest that it be replaced by 'H1-antihistamines'. The observations that H1-receptors modulate NF-kappaB activation and that there are complex interactions between GPCRs, has allowed us to postulate receptor dependent-mechanisms for some anti-inflammatory effects of H1-antihistamines, e.g. inhibition of ICAM-1 expression and the effects of bradykinin. Finally, the finding that blockade of HERG1 K+ channels is the mechanism by which some H1-antihistamines may cause cardiac arrhythmias has allowed the development of preclinical tests to predict such activity.

Inhibition of neurogenic inflammation by the Amazonian herbal medicine sangre de grado

This study was designed to determine if the Amazonian medicinal sangre de grado, confers benefit by suppressing the activation of sensory afferent nerves.

METHODS

(i) vasorelaxation of rat mesenteric arteries in response to calcitonin gene-related peptide; (ii) rat paw edema in response to protease- activating peptide receptor 2-activating peptide; (iii) rat paw hyperalgesia in response to low-dose protease-activating peptide receptor 2-activating peptide or prostaglandin E2; (iv) gastric hyperemia in response luminal capsaicin; (v) a clinical trial of a sangre de grado balm in pest control workers. The parent botanical was fractionated for evaluation of potential active components. In preconstricted rat mesenteric arteries, highly diluted sangre de grado (1:10,000) caused a shift to the right of the calcitonin gene-related peptide dose-response curve (p < 0.01). Paw edema in response to protease-activating peptide receptor 2-activating peptide (500 microg) was reduced by as single topical administration sangre de grado balm (1% concentration, p < 0.01) for at least 6 h. Hyperalgesia induced by either low-dose protease-activating peptide receptor 2-activating peptide (50 microg) or prostaglandin E2 was prevented by sangre de grado balm. A fraction possessing analgesic and capsaicin antagonistic properties was isolated and high-performance liquid chromatography and gas chromatography-mass spectrometry analysis indicated that it was a proanthocyandin oligomer. In pest control workers, sangre de grado balm (Zangrado) was preferred over placebo, for the relief of itching, pain, discomfort, edema, and redness in response to wasps, fire ants, mosquitoes, bees, cuts, abrasions, and plant reactions. Subjects reported relief within minutes. We conclude that sangre de grado is a potent inhibitor of sensory afferent nerve mechanisms and supports its ethnomedical use for disorders characterized by neurogenic inflammation.

Human skin mast cells: in vitro and in vivo studies

OBJECTIVE

This short review surveys our current knowledge on the development and heterogeneity of human mast cells, the distribution of mast cells within human skin and the properties of human skin mast cells both in vitro and in vivo. It also examines the effects of antihistamines in the wheal-and-flare response in the skin provoked by bradykinin.

RESULTS

Mast cells derive from mononuclear precursor cells which undergo their final phase of their differentiation in the tissues. In normal skin, mast cells, which are primarily of the MC(TC) subtype, occur in the greatest density in the superficial dermal zone. Like all other mast cells, human skin mast cells bind IgE with high affinity to specific FcepsilonRI receptors, but unlike those from lung, tonsils, adenoids or intestine, they also express the C5a receptor (CD88) and activation sites for substance P, VIP, somatostatin, and compound 48/80. Both IgE-dependent stimulation by activating tyrosine kinases, and non-immunologic stimulation by activating G-proteins induce a characteristic compound exocytosis resulting in the liberation of the preformed mediators. Production of prostaglandin D2 and leukotriene C4, however, occurs only with IgE-dependent stimulation. In vivo, dermal microdialysis and scanning laser Doppler imaging have been used to assess the role of histamine in the wheal-and-flare response. These techniques were also used to show that low concentrations of intradermal bradykinin release negligible quantities of histamine. The results showed that although the resultant flare was inhibitable by antihistamines, low concentrations of bradykinin released negligible quantities of histamine. This suggests a potentially novel mechanism of action of antihistamines that requires further detailed investigation.

The effect of rectal diclofenac on pruritus in patients receiving intrathecal morphine

In this prospective randomised study, pruritus and pain were evaluated in patients undergoing abdominal surgery in which intrathecal morphine was administered. Each patient received intrathecal morphine 0.3 mg prior to induction, followed by a standard anaesthetic. The patients were randomly allocated to one of two groups. One group received 100 mg of rectal diclofenac immediately post-induction. Patients receiving diclofenac had significantly lower pruritus scores at 30 min (p = 0.0076), 2, 4, 8 and 24 h postoperatively, as well as significantly reduced pain scores at each time point (p < 0.0001 at each study interval). Morphine consumption in the first 24 h was also significantly lower in this group. In conclusion, rectal administration of diclofenac significantly reduces the incidence and severity of postoperative pruritus. It also significantly reduces pain and further analgesic requirements postoperatively.

The effect of intravenous tenoxicam on pruritus in patients receiving epidural fentanyl

In this prospective randomised study, pruritus and pain were evaluated in patients undergoing abdominal surgery during which epidural fentanyl was administered. All patients had an epidural catheter inserted at the time of surgery. Epidural fentanyl 100 micrograms was administered intra-operatively and infused at a concentration of 2 micrograms.ml-1 for 48 h postoperatively. All patients received a standard anaesthetic and, in addition, the study group had a 20 mg bolus of tenoxicam intravenously, intra-operatively. Patients receiving tenoxicam demonstrated significantly lower pruritus and pain scores at 30 min, 2, 4, 8 and 24 h postoperatively as well as reduced pethidine requirements for breakthrough pain in the first 24 h. In conclusion, tenoxicam 20 mg significantly reduces the incidence and severity of postoperative pruritus in patients who received peri-operative epidural fentanyl. In addition, it significantly reduces pain and further analgesic requirements postoperatively.

Effects of H1 antagonists on the cutaneous vascular response to histamine and bradykinin: a study using scanning laser Doppler imaging

Histamine plays an important part in the cutaneous weal and flare response which underlies many allergic skin conditions. It has a direct effect on the local vasculature to promote vasodilatation and increase microvascular permeability and may also initiate the more widely spread neurogenic flare. Quantification of these responses and studies of the mediator mechanisms underlying them have been limited by the lack of appropriate techniques to investigate them. To address this we have used two relatively new techniques, scanning laser Doppler imaging (LDI) and dermal microdialysis to measure changes in skin blood flow and the release of histamine within the weal and flare, following intradermal injection of histamine or bradykinin. These measurements have been made both in the absence and presence of the H1 receptor blockers cetirizine and loratadine. Scanning LDI of the inflammatory response revealed marked differences in both the development and steady state responses to the intradermal injection of histamine (1-3 mumol/L) and bradykinin (1 mumol/L). The development of the flare and the weal response to both histamine and bradykinin was significantly reduced by cetirizine but not by loratadine. The histamine-induced flare area fell by 57 +/- 4% (mean +/- SEM, n = 10, P < 0.001) after cetirizine and the area of the weal fell by 73 +/- 11% (P < 0.009). Bradykinin-induced inflammatory responses were similarly reduced by cetirizine, the weal by 60 +/- 16% (P < 0.02) and the flare by 61 +/- 4% (P < 0.005). Measurement of histamine concentration in skin using microdialysis, in six subjects, confirmed that histamine levels rose in the dialysate collected from the weal to 310 +/- 16 nmol/L following injection of histamine. Histamine levels also rose following bradykinin injection in some subjects (mean 147 +/- 46 nmol/L, range 18-336). Little increase in histamine concentration was seen in the dialysate from the flare following injection of either histamine or bradykinin. The histamine concentration in dialysate from unprovoked skin was 4.19 +/- 0.75 nmol/L. These data reveal differences in the dermal responses to different mediators when assessed using scanning LDI. They confirm that histamine is released within the weal but not the flare response to the intradermal injection of both histamine and bradykinin and that its effects on the local vasculature to cause the oedematous weal and the axon reflex-mediated flare are significantly attenuated by the H1 antagonist cetirizine and to a lesser extent by the H1 antagonist loratadine.

Reduced skin hyperemia during tap water iontophoresis after intake of acetylsalicylic acid

Skin microcirculation and skin temperature of 10 healthy subjects (6 men and 4 women, 20-44 yr of age) without any vascular diseases were registered when a thermoindifferent tap water iontophoresis was applied. The aim of this controlled study was to evaluate the development of skin hyperemia after the intake of 500 mg of acetylsalicylic acid (ASA). The measurement was conducted by laser-Doppler flowmetry on the proximal forearm. The skin temperature was measured before and after the treatment by an infrared thermometer. In all persons there was an intense erythema on the side of the cathode and only a modest one on the side of the anode. Without ASA preliminary treatment, the cutaneous flow showed an increase of 106% at the anodal side and that of 834% at the cathodal side (P < 0.001). After ending tap water iontophoresis, the skin temperature increased more on the cathode side than on the anode side (P < 0.001). After the intake of 500 mg ASA, the increase of the flow was 78% at the anode and 88% at the cathode. The comparison of the skin microcirculation did not show any differences at the anodal side when acetylsalicylic acid was taken before, but a strong suppression of the galvanic erythema at the cathodal side was observed after the intake of ASA. There is a direct influence of acetylsalicylic acid on the induction of the neurogenic inflammation caused by a galvanic erythema. The intensity of the induced erythema correlates with the analgesic effects of constant current treatment. An attenuation of the electrotherapeutic analgesia is possible.

In vivo drug-response measurements in target tissues by microdialysis

To study the suitability of the microdialysis technique for the measurement of target tissue pharmacodynamics in humans, the model compounds theophylline, milrinone, and compound 48/80 were administered locally by means of reversed microdialysis to the interstitial space of skeletal muscle or skin in 24 healthy volunteers. Simultaneously, interstitial concentrations of cyclic adenosine monophosphate (cAMP; as an indicator of phosphodiesterase activity) were measured in skeletal muscle, and interstitial concentrations of histamine (as an indicator of mast cell release) were measured in skin. In muscle, reversed microdialysis with milrinone led to a dose-dependent increase in interstitial cAMP concentrations (n = 8), whereas no significant effect on cAMP was observed for theophylline versus placebo (1.63 +/- 0.53 nmol/L; n = 6), even at local concentrations exceeding those attained after therapeutic doses. In skin, reversed microdialysis with compound 48/80 increased interstitial histamine concentration dose dependently versus placebo (5.99 +/- 2.74 nmol/L; n = 10). From our experiments in human skeletal muscle and skin, we concluded that microdialysis was a suitable technique for the characterization of in vivo drug response at the relevant target site. Extension of these measurements to several other human tissues is readily feasible.

Effect of octreotide, a somatostatin analogue, on release of inflammatory mediators from isolated guinea pig bladder

OBJECTIVE

Somatostatin has been demonstrated to inhibit inflammation under certain circumstances. We hypothesized that in vivo treatment with octreotide, a long-acting analogue of somatostatin analogue, would diminish the capacity of inflammatory peptides to stimulate in vitro release of inflammatory mediators by the bladder.

METHODS

Female guinea pigs were injected with octreotide (20 mg./kg. i.m.) prior to euthanasia. Control guinea pigs received no treatment prior to euthanasia. Urinary bladders were removed and incubated with substance P (SP, 10 microM), neurokinin A (NKA, 10 microM), or bradykinin (BK, 10 microM) in the presence or absence of indomethacin (50 microM), and release of histamine, prostaglandins (PGE2 and PGF2 alpha), and leukotriene (LTB4) was determined.

RESULTS

Sensory peptides and BK induced time-dependent release of histamine and eicosanoids from isolated urinary bladder. Blockade of cyclooxygenase with indomethacin (50 microM) abolished peptide-induced prostaglandin release but enhanced LTB4 release. In vivo octreotide pretreatment decreased peptide-induced histamine release, had no effect on PGE2 or PGF2 alpha release, and LTB4 release. However, octreotide prevented the increase in LTB4 release in tissues incubated with indomethacin.

CONCLUSIONS

These results indicate that somatostatin has the capacity to suppress the release of histamine and prevents potentiation of LTB4 release by indomethacin by the guinea pig bladder in response to pro-inflammatory peptides, indicating that somatostatin may be useful in preventing or treating some forms of cystitis.

Pruritus--itching for a cause and relief?

The mechanisms of pruritus, an unpleasant irritation on the skin that provokes an urge to scratch, are reviewed. Whilst symptomatic treatment is only partially effective, antihistamines remain the first choice of treatment. However, recent novel treatment using opiate antagonists, propofol (subhypnotic doses) and serotonin antagonists offer attractive alternatives.

Increased sensitivity to bradykinin among African Americans

BACKGROUND

Angioedema is a potentially life-threatening side effect of angiotensin-converting enzyme (ACE) inhibitors. Although the mechanism of angioedema is not certain, bradykinin has been implicated in its pathogenesis. Compared with Caucasians, African Americans are at an increased risk of ACE inhibitor-associated angioedema, independent of ACE inhibitor dose or concurrent medications. Because urinary kallikrein levels are decreased in African Americans with hypertension, we hypothesized that endogenous bradykinin levels may be decreased in African Americans and that they therefore may be more sensitive to ACE inhibitor-induced increases in bradykinin or to exogenous bradykinin.

OBJECTIVE

To test this hypothesis, we measured the wheal response to intradermal injection of bradykinin in salt-replete hypertensive and normotensive African Americans and Caucasians.

METHODS

Two doses of bradykinin, 1 microgram and 10 micrograms, were administered on separate days in a randomized, double-blind fashion.

RESULTS

Higher bradykinin dose (analysis of variance: F = 38.33, p < 0.001), African American race (analysis of variance: F = 17.90, p < 0.001), and hypertension (analysis of variance: F = 4.37, p = 0.05) were all associated with an increased wheal response to bradykinin.

CONCLUSION

These data provide additional support for racial differences in the kallikrein-kinin system and also implicate abnormalities of the tissue kallikrein-kinin system in essential hypertension.

Tachyphylaxis develops to bradykinin-induced plasma extravasation in the rat

Bradykinin, an inflammatory mediator produced from plasma kallikreins, has potent effects on vascular functions, including increasing plasma extravasation and vasodilation. Attenuation in the response (desensitization to maintained exposure or tachyphylaxis to repeated administration) to bradykinin actions on synovial vasculature, a critical variable with respect to the role of bradykinin in sustained or chronic synovial inflammation, has not been elucidated. In the present study, we determined if tachyphylaxis and desensitization for bradykinin-induced plasma extravasation in the knee joint occur. Bradykinin-induced plasma extravasation into the knee joint cavity was determined spectrophotometrically by measuring the concentration of Evans blue dye extravasation into the joint perfusate. To examine for the development of tachyphylaxis, perfusion of bradykinin (160 ng/ml) was repeated after a 40-min wash with normal saline. Continuous intra-articular perfusion of bradykinin produced an increase in plasma extravasation that remained relatively stable with only a small, approximately 15 percent, decrease over 170 min. On the other hand, the levels of plasma extravasation produced by intermittent perfusion of bradykinin were dramatically lower than that induced by the first exposure (i.e., tachyphylaxis). We conclude that bradykinin-induced plasma extravasation develops marked tachyphylaxis but only minimal desensitization.

Role of bradykinin B2 receptors and mast cells in the bradykinin-induced skin response in the rat

We investigated the role of activation of bradykinin receptors and mast cells in the microvascular leakage of the vessels of the skin induced by the intracutaneous (i.c.) injection of bradykinin in the rat. We evaluated the effects of HOE140 (D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]bradykinin), a bradykinin B2 receptor antagonist, and ketotifen (4-(1-methyl-4-piperidylidene)4H-benzo[4,5]cyclohepta[1, 2-b]thiophen-10(9H)-one hydrogen fumarate), a histamine H1 receptor antagonist with mast cell stabilizing properties, on the skin response. Evans blue dye extravasation served as an index of the increase in vascular permeability. Bradykinin (2-100 nmol/site i.c.) induced the extravasation of Evans blue dye in a dose-dependent manner. Ketotifen (20 mg/kg i.p.) significantly inhibited the leakage of dye induced by bradykinin (10 nmol/site i.c.) by 66.2%, while HOE140 (1 mg/kg i.v.) had no effect. The concomitant injection of HOE140 (0.2, 2 nmol/site) and bradykinin (10 nmol/site i.c.), also did not significantly reduce the extravasation of dye. We conclude that the extravasation of plasma induced by the i.c. injection of bradykinin is mediated mainly by stimulation of the skin mast cells, but not by bradykinin B2 receptors.

Effects of prostaglandin E2 on the intensity of bradykinin-evoked pain from skin and veins of humans

Prostaglandin E2 increases bradykinin-induced spike activity from polymodal nociceptors of the skin and deep tissues in animals, suggesting sensitization of these receptors. To see whether these neurophysiological observations in animals correspond with increased pain intensity in humans, and whether also vascular nociceptors are sensitized, we studied in humans the effects of prostaglandin E2 on the intensity of pain evoked by bradykinin via the nociceptive systems of skin and veins. In seven healthy subjects, bradykinin was injected into the skin and into a vascularly isolated hand vein segment, prior to and after local application of prostaglandin E2. Subsequent pain intensity was recorded continuously with an electronically controlled visual analogue scale. Prostaglandin E2 alone never elicited pain, but without exception increased the intensity of bradykinin-induced pain in a concentration-related manner at concentrations from 10(-9) to 10(-6) M, both in skin and veins. Thus, bradykinin is more painful after pretreatment with prostaglandin E2, suggesting sensitization of nociceptors of the skin, but also of hand veins in humans.

Exogenous but not endogenous substance P releases histamine from isolated human skin fragments

Neuropeptides such as substance P are released from nerve terminals following the stimulation of sensory fibers, and are thought to participate in neurogenic inflammation in the skin; it is often speculated that mast cell activation is an intermediate step in this process. In the present study we addressed this hypothesis using freshly obtained skin explants derived from human neonatal foreskins or adult skin resections. The results demonstrate that when substance P is released from human skin by incubation in the presence of capsaicin (10(-5)M), no histamine is released from human isolated skin fragments. In each experiment human recombinant stem cell factor and/or exogenously applied substance P effectively evoked histamine release from the explants, attesting to the viability of the mast cells in the preparation. The concentrations of exogenously applied substance P required to elicit histamine release, however, were large (> 10 microM). These results indicate that substance P released from cutaneous sensory nerve fibers does not reach sufficient concentrations in the skin to degranulate mast cells. These data support the hypothesis that the vascular effects of neurogenic inflammation occur independently of mast cell activation.

Neuropeptides in skin

Neuropeptides are a heterogeneous group of more than 50 molecules that play a role in various cutaneous functions and diseases; they act as neuromodulators, neurotransmitters, neurohormones, and hormones. In the skin, neuropeptides are synthesized locally (i.e., in keratinocytes and in endothelial cells) and are transported by nerve fibers or immune cells (i.e., lymphocytes, monocytes, and polymorphonuclear cells). Specific receptors and binding sites for neuropeptides have been described in different cell lines in the skin (keratinocytes, endothelial cells, immune cells, fibroblasts). Many different biologic actions of neuropeptides have been demonstrated. Depletion of cutaneous neuropeptides (i.e., with capsaicin cream) or therapeutic use of neuropeptide agonists and/or antagonists may aid in the treatment of skin diseases.

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.

Tetracaine attenuates irritancy without attenuating desensitization produced by intravesical resiniferatoxin in the rat

The irritancy of initial application of capsaicin and related substances limits their therapeutic potential as novel analgesics. The purpose of the present study was to determine whether the irritant properties of the potent, capsaicin-like compound resiniferatoxin (RTX) would be attenuated by pretreatment with a local anesthetic and to determine whether the local anesthetic had significant effects on RTX-induced desensitization of sensory afferents. A model of visceral nociception in which irritants are instilled directly into the bladder (intravesical, i.ves.) of awake, freely moving rats was used. The nociceptive response, abdominal licking (grooming) was scored for 15 min; locomotor activity was scored concurrently. Tetracaine (0.125-1.0%) attenuated the increases in abdominal licking produced by RTX (3.0 nmol) in a dose- and time-dependent manner. At high doses, tetracaine also suppressed locomotor activity. Thirty minutes and 24 h later, the same dose of RTX was administered again to assess development of desensitization of bladder sensory afferents. Rats that had been pretreated with saline showed decreases in licking behavior from the first to subsequent injections of RTX, indicating the development of desensitization. Tetracaine-pretreated rats showed equivalent or significantly greater decreases in licking behavior, suggesting that local anesthetic pretreatment either did not alter or enhanced development of desensitization to RTX. In a second experiment, tetracaine (0.25 or 0.5%) produced similar effects against a high dose of RTX (3.0 nmol), but did not consistently alter excitatory or desensitizing effects of a low dose of RTX (0.1 nmol).(ABSTRACT TRUNCATED AT 250 WORDS)

Sensory neuropeptide release by bradykinin: mechanisms and pathophysiological implications

Bradykinin (BK) and related kinins excite primary sensory neurons, thus leading to the activation of sensory impulses. More recently, both functional and neurochemical evidence have been accumulated that BK evokes release of neuropeptides, including calcitonin gene-related peptide and the tachykinins substance P and neurokinin A, from peripheral terminals of capsaicin-sensitive primary afferents. The present article will review the mechanisms and the pathophysiological implications of the ability of BK to release sensory neuropeptides at the peripheral level. An account of the clinical studies performed on this subject will be also given.