Mechanisms of the flare reaction in human skin

Towards bridging the translational gap by improved modeling of human nociception in health and disease

Despite numerous studies which have explored the pathogenesis of pain disorders in preclinical models, there is a pronounced translational gap, which is at least partially caused by differences between the human and rodent nociceptive system. An elegant way to bridge this divide is the exploitation of human-induced pluripotent stem cell (iPSC) reprogramming into human iPSC-derived nociceptors (iDNs). Several protocols were developed and optimized to model nociceptive processes in health and disease. Here we provide an overview of the different approaches and summarize the knowledge obtained from such models on pain pathologies associated with monogenetic sensory disorders so far. In addition, novel perspectives offered by increasing the complexity of the model systems further to better reflect the natural environment of nociceptive neurons by involving other cell types in 3D model systems are described.

Acetylcholine-induced whealing in cholinergic urticaria - What does it tell us?

BACKGROUND

Cholinergic urticaria (CholU) is characterized by the occurrence of itchy wheals induced by sweating. Intradermal injections of acetylcholine (ACh) have been proposed to help with diagnosing CholU and subgrouping of patients, but controlled studies are largely missing.

OBJECTIVE

To compare the rates of positive ACh test results in well characterized CholU patients and controls and to identify clinical features of CholU linked to ACh reactivity.

METHODS

Acetylcholine was injected intradermally into 38 CholU patients and 73 matched healthy controls. Wheal and flare skin responses were assessed after 15 and 30 min and correlated with clinical features of CholU.

RESULTS

At 15 min after intradermal injections of ACh, wheal and flare responses were significantly more frequent in CholU patients than healthy controls, wheals: 34 % vs.15% (P = 0.028); flares: 50 % vs.18 % (P <0.001). Also, wheals were 37 % and flares 172 % larger and of longer duration in CholU patients than in healthy controls (both P < 0.01). CholU patients with ACh-induced wheals (ACh⁺) had larger flare but not wheal responses in response to histamine than those without (ACh^-; P = 0.011). Also, ACh-induced wheal responses were significantly correlated with sweating (r = 0.54, P = 0.046) in CholU patients. Finally, wheal responses lasted longer in ACh⁺ than in ACh^- patients (P = 0.03).

CONCLUSION

Intradermal ACh testing does not allow for the identification of CholU patients due to its low sensitivity. ACh-induced wheals, in patients with CholU, is linked to sweating and longer lasting symptoms. Intradermal ACh testing is an interesting tool for mechanistic studies in CholU.

Flare Size but Not Intensity Reflects Histamine-Induced Itch

INTRODUCTION

Flare reactions arise due to the release of vasodilators from sensory nerves caused by antidromic transmission of action potentials after the induction of itch.

OBJECTIVE

We investigated the link between flare and itch using 3 models of itch.

METHODS

Skin provocations with histamine, capsaicin, and cowhage were performed in 31 subjects. Itch was quantified using the visual analog scale. Flare was assessed using laser speckle contrast imaging (LSCI) and digital photography.

RESULTS

The duration, intensity, and area under the curve of histamine-induced itch correlated with the area of increased blood flow measured with LSCI (r = 0.545, p = 0.002; r = 0.575, p = 0.001; and r = 0.649, p < 0.001, respectively). Itch and skin blood flow in response to capsaicin or cowhage did not correlate.

CONCLUSION

In histamine-induced skin inflammation, itch and increased blood flow are linked. Thus, the area of histamine-induced flare may be used as a surrogate marker for histamine-induced itch.

Neuronal Regulation of Cutaneous Immunity

The skin is innervated by numerous sensory afferent neurons that respond to a diverse array of stimuli ranging from gentle touch to noxious pain. Various features of the immune system-pathogen recognition, secretion of soluble mediators-are shared with the nervous system. This has led to the recognition that neurons share some functions with innate immune cells and have the capacity to recognize pathogens and participate in innate immune responses. Neuroimmune interactions are bidirectional. Soluble mediators from immune cells activate neurons and soluble mediators from neurons can activate immune cells. In this review, we will focus on the interplay between neurons and innate immunity in the skin in the context of host defense and inflammation.

Deep inferior epigastric perforator flap demonstrating the triple response of Lewis phenomenon - A case report and insights into aetiology

Dermatographism, also known as skin writing, is an immunological response that remains an enigma. It occurs when normal skin is stroked with a dull object causing it to become raised and inflamed, and assume the shape of the stroke. Here we present a case of dermatographia in a denervated deep inferior epigastric perforator flap used to reconstruct breast tissue following mastectomy.

Photoactivation of olfactory sensory neurons does not affect action potential conduction in individual trigeminal sensory axons innervating the rodent nasal cavity

Olfactory and trigeminal chemosensory systems reside in parallel within the mammalian nose. Psychophysical studies in people indicate that these two systems interact at a perceptual level. Trigeminal sensations of pungency mask odour perception, while olfactory stimuli can influence trigeminal signal processing tasks such as odour localization. While imaging studies indicate overlap in limbic and cortical somatosensory areas activated by nasal trigeminal and olfactory stimuli, there is also potential cross-talk at the level of the olfactory epithelium, the olfactory bulb and trigeminal brainstem. Here we explored the influence of olfactory and trigeminal signaling in the nasal cavity. A forced choice water consumption paradigm was used to ascertain whether trigeminal and olfactory stimuli could influence behaviour in mice. Mice avoided water sources surrounded by both volatile TRPV1 (cyclohexanone) and TRPA1 (allyl isothiocyanate) irritants and the aversion to cyclohexanone was mitigated when combined with a pure odorant (rose fragrance, phenylethyl alcohol, PEA). To determine whether olfactory-trigeminal interactions within the nose could potentially account for this behavioural effect we recorded from single trigeminal sensory axons innervating the nasal respiratory and olfactory epithelium using an isolated in vitro preparation. To circumvent non-specific effects of chemical stimuli, optical stimulation was used to excite olfactory sensory neurons in mice expressing channel-rhodopsin (ChR2) under the olfactory marker protein (OMP) promoter. Photoactivation of olfactory sensory neurons produced no modulation of axonal action potential conduction in individual trigeminal axons. Similarly, no evidence was found for collateral branching of trigeminal axon that might serve as a conduit for cross-talk between the olfactory and respiratory epithelium and olfactory dura mater. Using direct assessment of action potential activity in trigeminal axons we observed neither paracrine nor axon reflex mediated cross-talk between olfactory and trigeminal sensory systems in the rodent nasal cavity. Our current results suggest that olfactory sensory neurons exert minimal influence on trigeminal signals within the nasal cavity.

Cutaneous TRPV1+ Neurons Trigger Protective Innate Type 17 Anticipatory Immunity

Cutaneous TRPV1⁺ neurons directly sense noxious stimuli, inflammatory cytokines, and pathogen-associated molecules and are required for innate immunity against some skin pathogens. Important unanswered questions are whether TRPV1⁺ neuron activation in isolation is sufficient to initiate innate immune responses and what is the biological function for TRPV1⁺ neuron-initiated immune responses. We used TRPV1-Ai32 optogenetic mice and cutaneous light stimulation to activate cutaneous neurons in the absence of tissue damage or pathogen-associated products. We found that TRPV1⁺ neuron activation was sufficient to elicit a local type 17 immune response that augmented host defense to C. albicans and S. aureus. Moreover, local neuron activation elicited type 17 responses and augmented host defense at adjacent, unstimulated skin through a nerve reflex arc. These data show the sufficiency of TRPV1⁺ neuron activation for host defense and demonstrate the existence of functional anticipatory innate immunity at sites adjacent to infection that depends on antidromic neuron activation.

Sentinel lymph node biopsy in small papillary thyroid cancer. A review on novel surgical techniques

PURPOSE

Sentinel lymph node biopsy (SNB) in patients with papillary thyroid carcinoma (PTC) and negative for clinically neck lymph node metastatic involvement (N0) has emerged as a promising minimally invasive procedure to detect metastatic nodes.

METHODS

The MEDLINE database was searched via the PubMed interface on 10 January 2018 for the MeSH headings "sentinel lymph node biopsy" and "thyroid carcinoma".

RESULTS

Vital blue dye, radioisotope, and the combination of both techniques are used in PTC patients. These methods and the emerging role of SPECT/CT are discussed in this review. The sentinel lymph node (SLN) identification rates ranged from 0 to 100% for blue dye, 83 to 100% for radioisotopes, and 66 to 100% for the combination of both techniques, respectively.

CONCLUSIONS

SNB based on radioisotope technique with the use of intraoperative gamma-probe is an accurate and safe method that allows the highest SLN detection rate. There is sufficient evidence to propagate the increasing use of SNB procedure that has the potential to avoid prophylactic lymph node surgery in patients clinically N0.

A historical perspective on the role of sensory nerves in neurogenic inflammation

The term ‘neurogenic inflammation’ is commonly used, especially with respect to the role of sensory nerves within inflammatory disease. However, despite over a century of research, we remain unclear about the role of these nerves in the vascular biology of inflammation, as compared with their interacting role in pain processing and of their potential for therapeutic manipulation. This chapter attempts to discuss the progress in understanding, from the initial discovery of sensory nerves until the present day. This covers pioneering findings that these nerves exist, are involved in vascular events and act as important sensors of environmental changes, including injury and infection. This is followed by discovery of the contents they release such as the established vasoactive neuropeptides substance P and CGRP as well as anti-inflammatory peptides such as the opioids and somatostatin. The more recent emergence of the importance of the transient receptor potential (TRP) channels has revealed some of the mechanisms by which these nerves sense environmental stimuli. This knowledge enables a platform from which to learn of the potential role of neurogenic inflammation in disease and in turn of novel therapeutic targets.

Stress-induced mast cell activation in glabrous and hairy skin

Mast cells play a key role in modulation of stress-induced cutaneous inflammation. In this study we investigate the impact of repeated exposure to stress on mast cell degranulation, in both hairy and glabrous skin. Adult male Wistar rats were randomly divided into four groups: Stress 1 day (n = 8), Stress 10 days (n = 7), Stress 21 days (n = 6), and Control (n = 8). Rats in the stress groups were subjected to 2 h/day restraint stress. Subsequently, glabrous and hairy skin samples from animals of all groups were collected to assess mast cell degranulation by histochemistry and transmission electron microscopy. The impact of stress on mast cell degranulation was different depending on the type of skin and duration of stress exposure. Short-term stress exposure induced an amplification of mast cell degranulation in hairy skin that was maintained after prolonged exposure to stress. In glabrous skin, even though acute stress exposure had a profound stimulating effect on mast cell degranulation, it diminished progressively with long-term exposure to stress. The results of our study reinforce the view that mast cells are active players in modulating skin responses to stress and contribute to further understanding of pathophysiological mechanisms involved in stress-induced initiation or exacerbation of cutaneous inflammatory processes.

Making sense of hypertrophic scar: a role for nerves

Healed partial thickness wounds including burns and donor sites cause hypertrophic scar formation and patient discomfort. For many patients with hypertrophic scars, pruritus is the most distressing symptom, which leads to wound excoriation and chronic wound formation. In spite of the clinical significance of abnormal innervation in scars, the nervous system has been largely ignored in the pathophysiology of hypertrophic scars. Evidence that neuropeptides contribute to inflammatory responses to injury include inflammatory cell chemotaxis, cytokine and growth factor production. The neuropeptide substance P, which is released from nerve endings after injury, induces inflammation and mediates angiogenesis, keratinocyte proliferation, and fibrogenesis. Substance P activity is tightly regulated by neutral endopeptidase (NEP), a membrane bound metallopeptidase that degrades substance P at the cell membrane. Altered substance P levels may contribute to impaired cutaneous healing responses associated with diabetes mellitus or hypertrophic scar formation. Topical application of exogenous substance P or an NEP inhibitor enhances wound closure kinetics in diabetic murine wounds suggesting that diabetic wounds have insufficient substance P levels to promote a neuroinflammatory response necessary for normal wound repair. Conversely, increased nerve numbers and neuropeptide levels with reduced NEP levels in human and porcine hypertrophic scar samples suggest that excessive neuropeptide activity induces exuberant inflammation in hypertrophic scars. Given these observations about the role of neuropeptides in cutaneous repair, neuronal modulation of repair processes at two extremes of abnormal wound healing, chronic non-healing ulcers in type II diabetes mellitus and hypertrophic scars in deep partial thickness wounds, may provide therapeutic targets.

Stimulation of mu and delta opioid receptors induces hyperalgesia while stimulation of kappa receptors induces antinociception in the hot plate test in the naked mole-rat (Heterocephalus glaber)

The antinociceptive effects of highly selective mu (DAMGO), delta (DPDPE) and kappa (U-50488 and U-69593) opioid agonists were evaluated following intraperitoneal (i.p.) administration in the naked mole-rat. A hot plate test set at 60 degrees C was used as a nociceptive test and the latency to the stamping of the right hind paw (response latency) was used as the end-point. DAMGO (5-10 mg/kg) and DPDPE (2.5-5 mg/kg) caused a naloxone-reversible significant decrease in the mean response latency. Subcutaneous injection of naloxonazine (20 mg/kg) 24h prior to the administration of DAMGO (5 mg/kg) also blocked the reduction in the response latency observed when DAMGO was injected alone. On the contrary, U-50488 (2.5-5 mg/kg) or U-69593 (0.08 or 0.1 mg/kg) caused a naloxone-reversible significant increase in the mean response latency. These results showed that activation of mu or delta receptors caused hyperalgesia, whereas activation of kappa receptors caused antinociception in the hot plate test in naked mole-rat. This suggests that mu and delta receptors modulate thermal pain in a different way than kappa receptors in the naked mole-rat. It is not possible at the moment to point out how they modulate thermal pain as little is known about the neuropharmacology of the naked mole-rat.

Somatosensory organization and behavior in naked mole-rats: II. Peripheral structures, innervation, and selective lack of neuropeptides associated with thermoregulation and pain

African naked mole-rats are subterranean rodents that have a robust orienting response to stimulation of unique vibrissa-like body hairs that are widely spaced over an otherwise hairless skin. To determine whether these large body hairs have a specialized organization similar to facial vibrissae, the structure and innervation of facial vibrissa follicles, body hair follicles, and intervening skin in naked mole-rats was compared with that in rats and a furred African mole-rat species (the common mole-rat). Immunofluorescence and lectin-binding analyses revealed that the body hair follicles in naked mole-rats were exceptionally large and well innervated, similar to guard hairs of furred species. However, these body vibrissae lacked the anatomic specializations and unique types of innervation affiliated with follicle sinus complexes of facial vibrissae. In contrast to the furred species, naked mole-rats had a paucity of Abeta-fiber Merkel endings at all peripheral locations. Naked mole-rats also were completely lacking in cutaneous C-fibers immunoreactive for substance P and calcitonin gene-related peptide. In contrast, the hairless skin of the naked mole-rats had an exceptional abundance of presumptive Adelta-fibers. The unusual features of the cutaneous innervation in naked mole-rats are presumably adaptations to their subterranean environment and that they are the only known poikilothermic mammal. The features of this mammalian model system provide unique opportunities to discriminate mechanisms related to tactile spatial orientation, vascular regulation, and nociception.

Kinetics of the superficial perfusion and temperature in connection with photodynamic therapy of basal cell carcinomas using esterified and non-esterified 5-aminolaevulinic acid

BACKGROUND

Photodynamic therapy (PDT) is a local treatment modality with increasing indications for various malignant and non malignant diseases. The treatment parameters have not yet been optimized as there is a need for a better understanding of the process. The skin is an important target and serves as a good model for monitoring and evaluating the interaction of light with biological tissue.

OBJECTIVES

The tissue perfusion and the temperature of basal cell carcinomas were measured in connection with PDT in order to investigate the biological mechanisms involved.

METHODS

An infrared camera was used during the treatment to measure skin temperature and a laser Doppler perfusion imaging device was used to image the superficial perfusion before and after treatment. Six hours after topical application of 5-aminolaevulinic acid (ALA) or methyl esterified ALA (ALA-ME), 38 basal cell carcinomas were treated using light from a diode laser at 633 nm.

RESULTS

In the lesions, the perfusion immediately after PDT was similar to that before PDT. One hour after the treatment the perfusion in the lesion was increased 50% compared with before PDT. However, in the skin surrounding the lesions the perfusion was doubled immediately after PDT and was still increasing 1 h after treatment. A temperature increase in the lesions of about 1-3 degrees C was observed for light fluence rates of 100-150 mW cm-2. In all patients treated, a diffuse temperature increase was visible outside the lesions. In some of the patients, the outlines of the blood vessels surrounding the treated lesions became visible in the thermal images. Measurements of temperature on healthy volunteers not administered photosensitizer, but illuminated with light of the same fluence rate, showed a similar increase in temperature in the illuminated spots. However, no temperature increase was observed outside the illuminated area. No statistically significant differences were found between the measurements on patients treated with ALA and ALA-ME.

CONCLUSIONS

The increased perfusion in the area surrounding the lesions after PDT, as seen by perfusion and temperature measurements, is the result of an inflammatory reaction to the PDT process. However, directly after PDT the perfusion in the lesions was the same as before irradiation. The combination of these observations suggests the presence of local blood stasis during and immediately after the treatment. The temperature measurements showed that the increased temperature was well below the temperature limit of hyperthermal damage. Furthermore, the measurements indicate that the increase in temperature was primarily a consequence of the heat absorbed in the tissue.

Innervation of supporting cells in the apical turns of the guinea pig cochlea is from type II afferent fibers

The outer supporting cells in the apical turns of the guinea pig cochlea receive a dense innervation. Our previous study (Fechner et al. [1998] J. Comp. Neurol. 400:299-300) suggested that this innervation of the Deiters' and Hensen's supporting cells was not derived from efferent fibers of the olivocochlear bundle, but its origin has not been further specified. To test the hypothesis that the innervation was afferent in origin, we traced apical afferent fibers that were retrogradely labeled by extracellular injections of horseradish peroxidase. Labeled afferent fibers were of two types: type I fibers contacted inner hair cells, whereas type II fibers crossed the tunnel and contacted outer hair cells. Significantly, most of the type II fibers also formed branches to the outer supporting cells. Although a few olivocochlear efferent fibers formed such branches, counts indicated that the overwhelming majority of the branches were produced by type II afferent fibers. These branches were not produced by basal type II fibers. Apical type II fibers also differed from basal fibers by having shorter lengths, spiraling both apically and basally, and contacting all three rows of outer hair cells. These innervation differences suggest differences in the ways that information from outer hair cells is processed in the apex versus the base of the cochlea.

Nervous control of blood flow in the orofacial region

The blood vessels of orofacial tissues are innervated by cranial parasympathetic, superior cervical sympathetic, and trigeminal nerves, a situation somewhat different from that seen in body skin. This review summarizes our current knowledge of the nervous control of blood flow in the orofacial region, and focuses on what we know of the respective roles of sympathetic, parasympathetic, and trigeminal sensory nerves in the regulation of blood flow in this region, with particular attention being paid to the mutual interaction between them.

Dense innervation of Deiters' and Hensen's cells persists after chronic deefferentation of guinea pig cochleas

Innervation of Deiters' and Hensen's cells has been described in the organ of Corti of several mammalian species and has been suggested to arise from the olivocochlear (OC) efferent system (Wright and Preston [1976] Acta Otolaryngol. 82:41-47). In the present study, antineurofilament immunostaining was used to reveal these outer supporting cell fibers (OSCFs) in the normal guinea pig. In control ears, OSCFs were absent in the basal half of the cochlea but increased in number steadily toward the apex, peaking at values of over 1,200 fibers/mm. These values indicate a far more profuse innervation of supporting cells than has been described previously, suggesting that most OSCFs were not stained in previous immunohistochemical studies. Chronic cochlear deefferentation was used to test whether OSCFs are part of the OC system. The OC bundle was transected unilaterally, and the animals were allowed to survive for 4-8 weeks. Completeness of deefferentation was assessed by using acetylcholinesterase staining of the brainstem and measurement of the density of OC fascicles in the cochlea. By using these metrics, unilateral deefferentation was nearly complete in three animals. In successfully deefferented cases, the OSCF innervation density was not statistically different from control values. We conclude that the vast majority of OSCFs are not of OC origin. We speculate that they may be branches of type II afferent fibers to outer hair cells and that a smaller population of OSCFs with different morphology and immunoreactivity may arise from the OC system.

Postherpetic neuralgia: irritable nociceptors and deafferentation

Postherpetic neuralgia (PHN) is a common and often devastatingly painful condition. It is also one of the most extensively investigated of the neuropathic pains. Patients with PHN have been studied using quantitative testing of primary afferent function, skin biopsies, and controlled treatment trials. Together with insights drawn from an extensive and growing literature on experimental models of neuropathic pain these patient studies have provided a preliminary glimpse of the pain-generating mechanisms in PHN. It is clear that both peripheral and central pathophysiological mechanisms contribute to PHN pain. Some PHN patients have abnormal sensitization of unmyelinated cutaneous nociceptors (irritable nociceptors). Such patients characteristically have minimal sensory loss. Other patients have pain associated with small fiber deafferentation. In such patients pain and temperature sensation are profoundly impaired but light moving mechanical stimuli can often produce severe pain (allodynia). In these patients, allodynia may be due to the formation of new connections between nonnociceptive large diameter primary afferents and central pain transmission neurons. Other deafferentation patients have severe spontaneous pain without hyperalgesia or allodynia and presumably have lost both large and small diameter fibers. In this group the pain is likely due to increased spontaneous activity in deafferented central neurons and/or reorganization of central connections. These three types of mechanism may coexist in individual patients and each offers the possibility for developing new therapeutic interventions.

Reflex parasympathetic vasodilatation in facial skin

1. The present report summarizes data from recent studies dealing with parasympathetic innervation of blood vessels in the lower lips (gingiva) of cats. 2. A study using the HRP tracing technique shows that blood vessels in the lower lip are innervated by postganglionic fibres originating in the otic ganglion, but not in the pterygopalatine ganglion. 3. There is a dual innervation of the cat lower lip by two groups of parasympathetic vasodilator fibres; in one case, fibres originating from the facial nerve root are distributed to the lower lip via chorda tympani nerve and in the other, fibres emanating from the glossopharyngeal nerve root project to the lower lip via the otic ganglion. 4. Parasympathetic reflex vasodilatation can be elicited by activation of the trigeminal (somatic), vagus (visceral), chorda tympani (gustatory) and nasal (chemical and mechanical) stimulation in the lower lips of cat. 5. Parasympathetic reflex vasodilatation elicited by somatic stimulation is mediated via the otic ganglion but not via the pterygopalatine ganglion, indicating that parasympathetic neurons, particularly those running as efferents in the glossopharyngeal nerve, are involved in the vasodilatation elicited by somatic, visceral and nasal stimulation.

Somatosensory stimulation causes autonomic vasodilatation in cat lip

1. Electrical stimulation of the infra-orbital nerve and the maxillary buccal gingiva caused an increase in ipsilateral lip blood flow in a stimulus intensity-dependent manner in anaesthetized cats. 2. The reflex vasodilator response was resistant to blockade by antimuscarinic (atropine), antiadrenergic (phentolamine and propranolol) and antihistaminergic (tripelennamine) but sensitive to ganglionic blocking agent (hexamethonium). 3. The reflex vasodilator response was unaffected by section of the ipsilateral cervical sympathetic trunk and facial nerve root, but was completely abolished by ipsilateral section of the glossopharyngeal nerve root. 4. The vasodilator response elicited by stimulation of the facial and glosso-pharyngeal nerves was never affected by lesion of the ipsilateral pterygopalatine ganglion. 5. Local anaesthesia or section of the inferior alveolar nerve abolished the vasodilator effects of stimulation of the facial and the glossopharyngeal nerves. 6. These results suggest that there is a somato-autonomic reflex vasodilator system mediated via final neurons that are not cholinergic, and that the parasympathetic vasodilator fibres emerge from the brain stem with the glossopharyngeal nerve and reach the blood vessels via the otic ganglion and the inferior alveolar nerve in the cat mandibular lip.

Effects of cilazaprilat and enalaprilat on experimental dermatitis in guinea pigs

Two non-sulfur containing ACE-inhibitors were tested concerning their local effect on experimental dermatitis in ovalbumin-sensitized guinea pigs. Enalaprilat but not cilazaprilat potentiated the ovalbumin-evoked inflammatory response. Furthermore, enalaprilat clearly enhanced the erythema evoked by substance P, whereas cilazaprilat did not. Concerning, the bradykinin-evoked erythema, enalaprilat significantly potentiated the response, whereas cilazaprilat only caused a slight increase. Our results suggest that different affinities for peptidases involved in degradation of inflammatory peptides can explain differences between the pro-inflammatory properties of enalaprilat and cilazaprilat.

Angiotensin-converting enzyme inhibitors and their influence on inflammation, bronchial reactivity and cough. A research review

Synthetic orally active angiotensin-converting enzyme (ACE) inhibitors have been successfully used in the treatment of congestive heart failure and hypertension, particularly in hypertensive subjects with increased renin-angiotensin-aldosterone-system activity. Adverse skin reactions, angioneurotic oedema and rapidly decreasing lung function in asthmatics have been reported following medication with ACE inhibitors. Furthermore, these drugs have been associated with a persistent dry cough in subjects without previous known bronchial hyper-reactivity. There is reason to believe that an ACE inhibitor-induced cough is due to an increased inflammatory state in the airways of susceptible individuals, and that this cough might thereby have pathophysiological features in common with the cough seen as an early symptom of asthma. All inflammatory responses, wheal and flare reactions, infiltration of neutrophils, eosinophils, basophils and monocytes were enhanced by ACE inhibitors. A dose-response relationship for the proinflammatory effect of the ACE inhibitor has been demonstrated.

Increased bronchial reactivity and potentiated skin responses in hypertensive subjects suffering from coughs during ACE-inhibitor therapy

The aim of this study was to investigate whether ACE-inhibitors could influence bronchial reactivity and interfere with inflammatory skin responses. Ten hypertensive subjects, who had reacted with coughs during ACE-inhibitor therapy, were treated in a double-blind crossover fashion for two weeks with enalapril and with placebo. Enalapril reduced the PC20 value for histamine and augmented the dermal response. Circulating eosinophilic leukocyte level in venous blood dropped markedly after the histamine bronchoprovocation performed during enalapril treatment. Plasma substance P was reduced after histamine provocation performed during placebo treatment, whereas this reduction was abolished by enalapril. In this study, we have demonstrated ACE-inhibitor-induction of moderately increased bronchial reactivity in subjects with suspected ACE-inhibitor-elicited coughs. It is suggested that coughing during ACE-inhibitor therapy is due to an increased inflammatory state in the airways.

Importance of beta 2-adrenoceptor stimulation in the suppression of intradermal antigen challenge by adrenaline

1. Seven atopic subjects received two injections of antigen and one of saline intradermally in the back on each of 4 separate days. They were pretreated with four different drug combinations: (a) adrenaline 0.3 mg subcutaneously over the deltoid muscle (b) subcutaneous adrenaline preceded by 5 mg of the specific beta 2-adrenoceptor antagonist ICI 118,551 orally (c) 8 mg of salbutamol orally (d) placebo. Tablets were given 2 h before and subcutaneous injections 15 min before the intradermal injections of saline and antigen. 2. The median flare response to intradermal low dose antigen and high dose antigen after pretreatment with adrenaline was 4% and 49% of the response seen following pretreatment with placebo (P less than 0.001). When adrenaline was preceded by ICI-118,551, the corresponding median flare responses were 2% and 44% (P less than 0.001) of the placebo response. The flare response after pretreatment with salbutamol was not significantly different from placebo. 3. Adrenaline suppressed the median weal response to the higher dose of antigen to 52% of the response after pretreatment with placebo (P less than 0.05). This suppression by adrenaline was blocked by pretreatment with ICI 118,551. The median weal response after the highest dose of antigen was suppressed by salbutamol to 66% of the response seen after placebo, although this was not significant even when a further three subjects were studied with either salbutamol or placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigation of mechanisms of the flare and wheal reactions in human skin by band method

Following intradermal injection of histamine, substance P or neurotensin into the normal human forearm skin at the site 0.5 cm proximal to the band, the flare response developed as quickly on the distal side as on the proximal side of the band, whereas the wheal reaction was localized on the proximal side. Pretreatment of skin with capsaicin dramatically inhibited the histamine-induced flare response but had no effect on nicotine-induced axon reflex sweating. The usefulness of the band method is discussed.

Potentiation of inflammatory reactions in guinea-pig skin by an angiotensin converting enzyme inhibitor (MK 422)

There have recently been reports of persistent cough and increased broncho-obstruction likely to have been induced by ACE inhibitors. In order to study the effect of MK 422 (the active parent diacid of enalapril) on the inflammatory response, ovalbumin-sensitized guinea-pigs were tested intradermally with ovalbumin, capsaicin and bradykinin. All inflammatory responses were enhanced by treatment with MK 422 for 2 days prior to testing as compared to the responses of control animals. Infiltration of neutrophils, eosinophils, basophils and monocytes was increased following ovalbumin challenge in the MK 422-treated animals. We suggest that skin reactions and airway symptoms noticed during ACE inhibitor therapy might have been due to induced or potentiated inflammatory reactions in the skin or in the bronchial wall.

Studies on histamine-induced cutaneous flare in the guinea pig

Evidence for the involvement of both H1- and H2-receptors in histamine-induced cutaneous flare reactions has been obtained. The guinea pig ear was used as the site of histamine injection since, unlike virtually all other skin areas in non-humans examined to date, it displays a similar response to that which occurs in human skin, namely the Lewis triple response. The flare reaction to histamine in the guinea pig ear was established as an indirectly mediated, neurovascular phenomenon by demonstrating that the vascular changes which occur in the region of the flare are incompatible with histamine directly stimulating the cutaneous vasculature and also by showing that histamine-induced cutaneous flare reactions are reduced by local anaesthesia. Having verified the authenticity of the flare reaction in the guinea pig ear, the role of H1- and H2-receptors in histamine-induced flare reactions was examined. Mepyramine and Cimetidine both significantly reduced the flare reaction produced by histamine. In addition, 2-(2-aminoethyl) pyridine, a selective H1-receptor agonist, was found to elicit a dose-dependent flare response.

Pain thresholds and electromyographic features of periarticular muscles in patients with osteoarthritis of the knee

Electrical stimulation pain thresholds and EMG activity were studied, using the vastus medialis muscle of healthy control subjects and of patients with osteoarthritis of the knee. Various categories of sensation elicited by progressive increases of the level of electrical stimulation (including one defined as pain threshold) were defined for control subjects. For patients, muscular pain thresholds differed significantly for the two sides of the body; they were usually lower in the more affected side. Involuntary activity of certain motor units and delayed relaxation following voluntary contraction were consistently observed in patients. The involuntary activity was affected by limb position and by mechanical stimulation of tender areas of the muscle or joint. Differences in pain threshold between the two sides were significantly reduced and the EMG pattern became normal following treatment with injections of local anaesthetic into tender periarticular areas and systemic administration of lysine acetylsalicylate. In standing patients, abnormal EMG activity (which was characteristically sensitive to body load and its variations) was found. Injection of a local anaesthetic into the joint cavity was able to induce a rapid subjective improvement and a consistent reduction of EMG activity.

Effect of topical indomethacin on allergen-induced dual skin reactions

Twelve asthmatics with dual bronchial and skin reactions after allergen challenge received topical treatment with a 5%-indomethacin cream half an hour before and up to 7 h after intradermal allergen and histamine injections. The erythema during the first 20 min of the wheal and flare reaction (WFR) was not affected, neither were the diameters of wheals and flares. 40 to 60 min after injection we observed a marked reduction of the erythema in histamine- and allergen-tested skin areas of 10 patients. This effect lasted up to the 5th h after injection of high allergen doses. During the fully developed late cutaneous reactions (LCR) no effect of indomethacin on the erythema was observed, the edema of LCR was only insignificantly reduced. These results suggest that the erythema in LCR between the 1st and 4th h is caused, at least in part, by local formation of prostaglandins.