The effect of topical turpentine on the functional properties of cutaneous afferents in the anaesthetized rat

Turpentine was applied to the rat dorsal hindpaw over 1.5-3.5 h and afferent activity was recorded for 1.5-7 h after its removal. Increased spontaneous activity from both A- and C-fibres was observed. There was an increase in units with no response to natural stimuli and a reduction in the numbers of all types of afferent unit, with some recovery of the C- and A delta-classes during the recording period. Surviving C-polymodal nociceptor units had normal sensitivity to noxious heat, but higher mechanical thresholds. Thus turpentine application caused no nociceptor sensitization. Instead, the many insensitive units plus the generalized spontaneous firing may be signs of non-specific axonal damage. A general division of irritant chemicals into those that are predominately damaging, like turpentine, and those that generate specific nociceptor firing or sensitization, is proposed.

Responses of rat spinal dorsal horn neurons to intracutaneous microinjection of histamine, capsaicin, and other irritants

To investigate the spinal processing of cutaneous pruritic and algesic stimuli, single-unit recordings were made from wide-dynamic-range-type lumbar spinal dorsal horn neurons in pentobarbital-sodium-anesthetized rats. Neuronal responses were recorded to mechanical and noxious thermal stimuli, as well as to microinjection (1 microl) of histamine (0.01-10% = 9 x 10(-1)-9 x 10(-4) M), capsaicin (0.1% = 3.3 x 10(-3) M), or other algesic chemicals into skin within the receptive field via intracutaneously placed needles. Most (84%) of the 89 neurons responded to intracutaneous (i.c.) microinjection of histamine with a brief phasic discharge followed by an afterdischarge of variable (s to min) duration. Ten minutes after i.c. microinjection of histamine (but not NaCl), there was a significant increase in the mean area of the low-threshold (but not high-threshold) portion of unit mechanical receptive fields. However, responses to graded pressure stimuli were not significantly affected after histamine. Responses did not exhibit significant tachyphylaxis when histamine microinjections were repeated at 5- or 10-min intervals. Unit responses significantly increased in a dose-related manner to microinjection of histamine at concentrations ranging across 4 orders of magnitude. Within 30 s after i.c. microinjection of the H1 antagonist cetirizine, unit responses to i.c. histamine delivered at the same skin site were significantly attenuated. Unit responses to histamine, as well as to noxious thermal stimulation, were significantly reduced after systemic administration of morphine (3.5 mg/kg i.p.) in a naloxone-reversible manner. Application of a mechanical rub, scratch, or a noxious heat stimulus during the unit's ongoing response to i.c. histamine produced a brief and marked excitation, often followed by a period of reduced ongoing discharge. Unit responses to histamine were markedly suppressed by electrical stimulation in the midbrain periaqueductal gray. Most (79%) histamine-responsive units tested also responded to i.c. microinjection of capsaicin. After the initial microinjection of capsaicin, subsequent responses to histamine and capsaicin microinjections were significantly reduced. Units also responded to i.c. ethanol (capsaicin vehicle) in a dose-related manner, and showed tachyphylaxis to repeated i.c. ethanol at 80% but not at 8%. The mean response to 80% ethanol was significantly smaller than to 0.1% capsaicin. All units tested also responded to topical application of mustard oil (50%) and i.c. serotonin (30 microg). The results are discussed in terms of theories that attempt to reconcile psychophysical and clinical observations of pain and itch sensation.

Differential inductive and suppressive effects of endotoxin and particulate irritants on hepatic and renal cytochrome P-450 expression

Inflammatory stimuli such as bacterial lipopolysaccharide (LPS) have been shown to down-regulate the mRNA and protein expression of hepatic cytochrome P-450 (P-450) isozymes 2C11, 2C12, 2E1 and 3A2 and to induce the mRNA expression of the P-450 4A subfamily. In this study, we examined the effects of irritants on the hepatic and renal expression of P-450 2C11, 2E1 and 3A2 and the 4A subfamily in the rat. Fischer 344 rats were administered doses of SiO2 (Celite), BaSO4, kaolin and LPS intraperitoneally and killed after different times for hepatic and renal RNA and microsome isolation. The administration of each irritant was found to suppress hepatic P-450 2C11 mRNA and protein and to induce P-450 4A1, 4A2 and 4A3 mRNA expression while having no significant effect on P-450 2E1 or 3A2. P-450 4A2, 4A3 and 2E1 mRNAs were all induced in the kidney cortices of the irritant- and LPS-treated rats. The effects of BaSO4 and SiO2 were found to be dose dependent. Chlorzoxazone-6-hydroxylase activity increased in the kidneys of irritant-treated rats, which is consistent with an increased expression of P-450 2E1. All irritants were found to induce the mRNA for the acute-phase protein fibrinogen; however, in contrast to LPS treatment, none of the irritants that were tested induced hepatic inducible nitric oxide synthase mRNA expression. These findings demonstrate the induction of renal P-450 isozymes after irritant and LPS administration. The findings of this study also suggest that different inflammatory stimuli affect the individual P-450 isozymes differentially.

Glial cell reactions in the spinal cord after sensory nerve stimulation are associated with axonal injury

Astroglial and microglial reactions in the dorsal and ventral horns of the adult rat spinal cord were studied after graded electrical stimulation of the rat sciatic nerve and after topical application of mustard oil to the hindlimb foot. Antibodies to glial fibrillary acidic protein and complement receptor 3 (OX-42) were used as markers for astroglia and microglia, respectively. The results showed that electrical nerve stimulation resulted in increased immunoreactivity for GFAP and OX-42 in the spinal cord dorsal and ventral horns only after the use of stimulation strengths which were associated with nerve fiber degeneration in the stimulated nerve. Application of mustard oil to the foot caused no changes in GFAP or OX-42 immunoreactivity. These findings indicate that peripheral nerve stimulation in itself is insufficient to induce astroglial and microglial responses in the spinal cord. The signal(s) mediating these responses, regularly seen after nerve injury, are therefore most probably not related to the afferent barrage of action potentials evoked by the injury.

Electron resonance studies on the influence of anionic surfactants on human skin

BACKGROUND

When skin is exposed to chemicals, raw materials interact with the lipid structure of the stratum corneum. At least two types of disorders can be distinguished--that of alkyl chains inside one lipid bilayer and that of lipid layer arrangement. Electron spin resonance (ESR) spectroscopy of a nitroxide spin label is a valuable method in the study of biological membranes.

OBJECTIVE

These experiments define the effect of anionic surfactants on the lipid bilayer of human stratum corneum.

METHODS

5-Doxyl stearic acid (5-DSA) was used as the spin label. Sodium lauryl sulfate (SLS) and sodium lauroyl-L-glutamate (SLG) were the anionic surfactants studied. ESR spectrum measurements of surfactant-treated stratum corneum were performed and order parameters calculated.

RESULTS

1% of SLS leads to an obvious change in ESR spectra--from strongly to weakly immobilized spectra. The molecular motion of spin labels (5-DSA) in SLS-treated stratum corneum is different from that of spin labels in the untreated stratum corneum. The ESR spectra suggest that SLS affects the spin label binding to the lipid membrane and causes an increase in the mobility of bilayers. On the other hand, there were minimal changes in ESR spectra of 1% of SLG-treated stratum corneum. An increase in fluidity of skin lipid bilayers suggests a decrease in the skin barrier function.

CONCLUSION

ESR may provide a facile and robust method to define the subclinical irritancy potential of anionic surfactants and other materials.

Use of XTT-assay to assess the cytotoxicity of different surfactants and metal salts in human keratinocytes (HaCaT). A feasible method for in vitro testing of skin irritants

Because of the increasing need of reliable skin irritation tests and in order to reduce the number of animal experiments, in vitro alternatives have to be developed. We studied four surfactants and five metal salts for their cytotoxic potency in HaCaT cells, a spontaneously immortalized human keratinocyte line. The endpoint used to assess cellular viability was metabolization of the tetrazolium salt XTT (2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide). The tested substances revealed a significant rank order of their cytotoxicity at an exposure time of 24 h. It was 1) benzalkonium chloride, 2) sodium lauryl sulphate, and 3) Tween 20 (polyoxyethylene sorbitanmonolaurate) and Tween 80 (polyoxyethylene sorbitanmonooleate), for the surfactants; and 1) potassium bichromate, 2) copper sulphate, 3) cobalt chloride and palladium chloride, and 4) nickel sulphate, for the metal salts. There is an excellent correlation to the rank order of their known irritative potency in vivo. Being practicable and effective, the presented XTT-assay on HaCaT cells would be well suitable for an initial orientating screening of substances, subsequently followed by irritation tests directly in humans.

[Results of studies of regulatory mechanisms of hematopoiesis in health and disease]

Local and distant hemopoietic regulatory mechanisms were studied under various emergencies (immobilization, cytostatic injection, radiation, etc.). There were common processes (cell migration, destruction, T-lymphocyte accumulation, activation of the microenvironment and hemopoietic precursors) forming the local basis for compensatory and adaptive reactions of bone marrow hemopoietic tissue. Emphasis is laid on the association of local mechanisms with the neuroendocrine system which inevitably becomes activated under extreme exposures. On exposure to irritants having no myeloinhibitory effect, neurotransmitters and hormones, mainly glucocorticoids and catecholamines cause the development of erythro- and granulocytopoietic hyperplasia due to stimulation of the hemopoiesis-inducing microenvironment (HIM). Under hemopoiesis-suppressing influences, catecholamine-induced activations of HIM's resistant elements is accompanied by simultaneous inhibition of hemopoietic cells and HIN's factors damaged by an irritant. Under these conditions hemopoietic separation caused by the heterogeneous effect of transmitters on the cell leads to imbalance of hemopoietic precursor proliferation and differentiation and, finally, to delayed hemopoietic tissue regeneration. At the same time, the neuroendocrine system does not seem to play a leading role as compared to the control intact hemopoiesis.

Rapid recovery from capsaicin desensitization during recurrent stimulation

Topical desensitization of the tongue was assessed during multiple bouts of exposure to capsaicin. In the first experiment subjects rated perceived irritation as 30 capsaicin stimuli (33 microM) were applied to the tongue tip in three blocks of 10, with 15 min breaks between blocks. Significant desensitization was measured at the beginning of the second and third blocks within each session. However, as stimulation continued within those blocks sensations of irritation grew toward undesensitized levels ('stimulus-induced recovery' (SIR)). Desensitization did not extend across days. The second experiment employed a 10-fold higher concentration of capsaicin (330 microM) to determine if SIR was limited to low levels of desensitization. SIR occurred as before within sessions, and the higher concentration produced desensitization across days that also exhibited recovery during the first block of stimuli on days 2 and 3. The third experiment included piperine, zingerone and citric acid as stimuli to determine if SIR was specific to capsaicin. Piperine produced SIR under conditions of both self- and cross-desensitization with capsaicin, whereas recovery failed to materialize with zingerone. Citric acid was not significantly cross-desensitized by capsaicin, so recovery could not be measured. Overall the results demonstrate that desensitization of the tongue produced by either capsaicin or piperine can be temporarily reversed if stimulation with either chemical is resumed for only a few minutes. The implications these findings may have for hypotheses about the mechanisms of capsaicin desensitization and sensitization as well as for clinical applications of capsaicin as a topical analgesic are discussed.

Mucosal irritation, adaptive cytoprotection, and adaptation to topical ammonia in the rat stomach

BACKGROUND

The urease-ammonia (NH4OH) system has been proposed to play a major role in the pathogenesis of the Helicobacter pylori-associated gastritis, but the mechanism of the mucosal damage has not been fully explained. This study was designed to examine possible adaptive cytoprotection and the adaptation of rat gastric mucosa to the irritant action of NH4OH and urease.

METHODS AND RESULTS

Single application of NH4OH alone in various concentrations (15-500 mM) caused concentration-dependent mucosal damage starting with 30 mM and reaching a maximum at 250 mM NH4OH, similar to that obtained with 100% ethanol; it was accompanied by a decrease in gastric blood flow (GBF) to approximately 30% of the normal value. When the mucosa was first exposed to the low, non-damaging concentration (15 mM) of NH4OH and then insulted with 100% ethanol, the extent of ethanol damage was greatly attenuated as compared with that caused by ethanol alone. This adaptive cytoprotection was accompanied by the rise in GBF and reversed, in part, by the pretreatment with indomethacin, an inhibitor of prostaglandin (PG)-cyclooxygenase; with L-NAME, a blocker of NO-synthase; or with capsaicin deactivating the sensory nerves. Damaging concentrations of NH4OH (125 mM) caused widespread mucosal damage after the first application, but with repeated insults with 125 mM NH4OH a gradual reduction in the mucosal lesions, accompanied by enhanced mucosal cell proliferation and over-expression of epidermal growth factor (EGF) (using immunocytochemistry) and mRNA of EGF (using trans-reverse polymerase chain reaction), were observed.

CONCLUSIONS

NH4OH alone damages gastric mucosa only at the concentration exceeding that found in H. pylori-infected stomachs, whereas at lower concentrations it acts as 'mild' irritant to induce adaptive cytoprotection. This adaptive cytoprotection appears to be mediated, in part, by endogenous PG, sensory nerves, and an arginine-NO-dependent pathway, and repeated applications of NH4OH induce gastric adaptation, probably mediated by enhanced expression of EGF and its receptors and by an increased cell proliferation.

The Microsponge Delivery System (MDS): a topical delivery system with reduced irritancy incorporating multiple triggering mechanisms for the release of actives

The Microsponge Delivery System (MDS) is a unique technology for the controlled release of topical agents and consists of macroporous beads, typically 10-25 microns in diameter, loaded with active agent. When applied to the skin, the MDS releases its active ingredient on a time mode and also in response to other stimuli (rubbing, temperature, pH, etc). MDS technology is being used currently in cosmetics, over-the-counter (OTC) skin care, sunscreens and prescription products. By delivering the active gradually to the skin, MDS-benzoyl peroxide formulations, for example, have excellent efficacy with minimal irritation. These are typical benefits from the use of the MDS.

In vivo exposure to nitrogen dioxide (NO2) induces a decrease in calcitonin gene-related peptide (CGRP) and tachykinin immunoreactivity in guinea-pig peripheral airways

The mammalian respiratory tract is densely innervated by sensory and autonomic fibres. Subsets of the nerves contain bioactive regulatory peptides, such as substance P, calcitonin gene-related peptide (CGRP), and neurokinins. The sensory nervous system responds to inhaled irritants, resulting in a release of neuropeptides and, thus, a decrease in the peptide immunoreactivity of the fibres. We examined the effects of inhaled nitrogen dioxide (NO2), a well-known indoor and outdoor air pollutant, on pulmonary sensory neuropeptides. Guinea-pigs were exposed for 4 h to 18 parts per million (ppm) NO2 or to air (n = 5 each). At the end of the exposure, they were killed with urethane and their lungs were fixed in 1% paraformaldehyde in phosphate-buffered saline. Cryostat sections were stained with antisera to an anatomical nerve marker, protein gene product (PGP) 9.5, and to CGRP and tachykinins, utilizing the avidin-biotinylated peroxidase method. In the noncartilaginous airways (diameter < 250 microns) of NO2-exposed animals, less tachykinin- and CGRP-immunoreactive nerve fibres were found compared with controls. No change was seen in the total nerve fibre distribution (PGP 9.5). It is concluded that the peptidergic nerves of guinea-pig peripheral airways are a sensitive indicator of exposure to nitrogen dioxide.

Is cytokine expression responsible for differences between allergens and irritants?

Irritant and allergic contact dermatitis are two very similar diseases, and differentiating between these two can be difficult clinically. Recently, cytokines have been identified as useful tools for differentiation. Thus, our laboratory has identified an early cytokine pattern in the induction phase of contact sensitivity that is specific for allergens and is not found after epicutaneous application of irritants or tolerogens. The up-regulation of the Langerhans' cell-derived signal interleukin (IL)-1 beta early after allergen application especially seems to be highly specific for contact allergens. This cytokine was also found to be essential for the development of epicutaneous sensitization because injection of an anti-IL-1 beta monoclonal antibody before epicutaneous application of an allergen prevented sensitization. Additionally, cytokines also seem to be involved in down-modulating an ongoing inflammatory reaction such as contact sensitivity. IL-10 especially was shown to inhibit the LC accessory functions and to down-modulate inflammatory cytokines. The homeostasis of proinflammatory and counterregulatory cytokines and their clinical implications are discussed in this review.

Peeling agents and irritants, unlike tretinoin, do not stimulate collagen synthesis in the photoaged hairless mouse

Tretinoin has been shown to stimulate the synthesis of collagen in photo-aged human and hairless mouse skin. It has been suggested that this partial reversal of photodamage by tretinoin is a consequence of low-grade inflammation. The purpose of this study was to compare the effect of tretinoin with a number of irritants and peeling agents on collagen synthesis. Hairless mice were irradiated thrice weekly for 10 weeks with UVB. In the 10-week postirradiation period, the mice were treated topically five times per week with tretinoin (0.05%), glycolic acid (10%), benzalkonium chloride (1.0%), sodium lauryl sulfate (5%), croton oil (5%) and the water - propylene glycol vehicle. Microscopic measurements showed that the tretinoin-induced zone of new collagen was twice the depth of that induced by irritants or vehicle. The salt-soluble collagen content was determined by HPLC analysis of hydroxyproline levels. Type III procollagen was quantified by radioimmunoassay. Tretinoin-treated skin had increased amounts of collagen and type III procollagen whereas irritant- and peeling agent-treated skins were similar to vehicle-treated controls. Immunofluorescence studies were confirmatory. These results demonstrate that these agents, unlike tretinoin, do not have the capacity to enhance collagen synthesis. Therefore, it is likely that the effect of tretinoin does not depend upon irritation.

Psychophysical responses to single and multiple presentations of the oral irritant zingerone: relationship to frequency of chili consumption

There are few data on the psychophysical properties of zingerone, one of the pungent components in ginger, particularly in contrast to capsaicin. The time-intensity characteristics of zingerone irritation were examined using high-frequency, intermediate-frequency, and low-frequency users of chili, who rated the intensity of whole-mouth rinses of 1% zingerone at 6-s intervals for 3 min. Maximum intensity was reached within the first 20 s, while the zingerone was in the mouth. At this stage, there were no differences between groups. Following expectoration at 30 s, frequent users showed a more rapid decline in rated intensity than did intermediate users, who showed a more rapid decline than infrequent users. Capsaicin sensitization and desensitization are dependent upon the interstimulus intervals (ISIs) used. A second experiment, also using groups of high-, intermediate-, and low-frequency chili users, examined whether sensitization to zingerone could be demonstrated using ISIs based on the point of maximum intensity observed in the first study. In contrast to sensitization effects found with capsaicin, slight desensitization was observed over 10 successive zingerone stimuli. Following a 5-min hiatus in stimulation, further desensitization was observed over 10 results point to the ability of zingerone to self-desensitize, although the effect is of a smaller magnitude than that of capsaicin. None of these effects varied as a function of chili use. Analysis of the qualities that constituted zingerone irritation found that the sensations produced are predominantly burning and warmth, making it qualitatively similar to capsaicin.

Vagal bronchopulmonary C-fibers and acute ventilatory response to inhaled irritants

Experiments were carried out in anesthetized Sprague-Dawley rats to determine the role of vagal bronchopulmonary C-fiber afferents in regulating the respiratory responses to inhaled irritants. Spontaneous inhalation of 2 tidal breaths of a known airway irritant (sulfur dioxide, 0.5%; ammonia, 1%; cigarette smoke, 50%) into the lower airways invariably elicited an immediate and transient inhibitory effect on breathing, characterized by apnea or bradypnea and accompanied by bradycardia, which lasted for 3-8 breaths. A delayed hyperpnea was also induced by inhalation of cigarette smoke, but not by sulfur dioxide or ammonia. After perineural capsaicin treatment of both cervical vagi to selectively block the conduction of capsaicin-sensitive C-fibers, these inhaled irritants no longer evoked any inhibitory effect on breathing; conversely, an augmented inspiration was triggered within the first 3 breaths from the onset of cigarette smoke inhalation in > 85% of the rats studied, but after a delay of several breaths following inhalation of ammonia or sulfur dioxide in only 30% of the rats. The augmented breaths were completely abolished when both cervical vagi were cooled to 6-7 degrees C. Bilateral vagotomy eliminated all the immediate responses to these irritants. These results suggest that both vagal C-fiber endings and irritant receptors in the airways are activated by these inhaled irritants, but the more dominant and consistent inhibitory effect on breathing is elicited primarily by stimulation of C-fiber afferents.

Sodium lauryl sulfate effect on the density of epidermal Langerhans cells. Evaluation of different test models

The effect of different test models for sodium lauryl sulfate (SLS)-induced irritant contact dermatitis on epidermal Langerhans cells (LC) numbers was examined. Finn Chambers, 8 and 12 mm, containing 15 and 34 or 50 microliters, respectively, of 1% aq. solution of SLS were applied to human forearm skin for 48 h as single or repeated application. The results showed a clear difference between the effects with the 2 chamber sizes. The effect of the 8-mm chambers could result in increased, unchanged or decreased LC numbers, while 12-mm chambers always produced a decrease. These results seem to explain, at least partly, the discrepant results reported from various laboratories.

Correlation of impedance response patterns to histological findings in irritant skin reactions induced by various surfactants

We have explored the use of measurements of electrical impedance to discriminate between the effects of different irritant substances upon the skin, and have studied the relationships between impedance and histopathological change. Three compounds with different chemical profiles were tested on volunteers: sodium lauryl sulphate, benzalkonium chloride and nonanoic acid. The concentrations selected were such that each irritant produced responses of a similar order, as judged by visual scores. The magnitude and phase of electrical impedance were measured and, for comparison, also the transepidermal water loss. Four physically distinct aspects (indices) were devised from the impedance data, and the values obtained were statistically analysed. The three irritants produced different effects, giving distinctive impedance patterns. These were also found to be reflected by three different types of histopathological skin response. Our results suggest that the indices can be used to classify irritant contact reactions, which it is difficult or impossible to achieve by other non-invasive techniques.

Cyclooxygenase induction is essential for NGF synthesis enhancement by NGF inducers in L-M cells

Nerve growth factor (NGF) inducers, for example, 4-methylcatechol, pyrroloquinoline quinone, kansuinin A, and ingenol triacetate, stimulate NGF synthesis in L-M cells, but the mechanism of NGF induction by NGF inducers is not known. Using the four different types of previously described NGF inducers, we proved induction of cyclooxygenase activity by NGF inducers and detected prostaglandins D2 and E2 as metabolites of arachidonic acid. From the observation that the induction of NGF by each NGF inducers was inhibited by cyclooxygenase inhibitors or dexamethasone, cyclooxygenase activation is supposed to be an essential process for NGF induction.

Airway protective reflexes elicited by laryngeal ammonia: role of C-fiber afferents

Intralaryngeal ammonia induces an airway protective reflex in rats characterized by apnea, bradycardia and increased laryngeal resistance. Since ammonia is known to stimulate both the myelinated and the nonmyelinated afferents, the role of nonmyelinated afferents in eliciting the above response is unclear. The present study was designed to investigate this by utilizing two techniques that selectively block C-fiber afferents: intravenous ruthenium red and perineural application of capsaicin. Ammonia vapor was introduced into the functionally isolated larynx of anesthetized rats for 10 sec at a flow rate of 5 ml/sec. Changes in expiratory duration were expressed as the ratio between test and control expiratory time (TEmax/control). Perineural application of capsaicin (n = 8) to SLNs attenuated the responses of both intralaryngeal ammonia (TEmax/control: 12.32 +/- 1.67 to 6.89 +/- 1.62; P < 0.05) and capsaicin (8.86 +/- 2.02 to 3.35 +/- 2.17; P < 0.05). Pretreatment with ruthenium red (1 mg/kg, iv., n = 10) significantly reduced the effects of ammonia (20.43 +/- 4.38 vs. 11.66 +/- 3.21; P < 0.05) and nebulized capsaicin (16.28 +/- 4.58 to 3.90 +/- 0.83; P < 0.05). These results suggest that the C-fiber endings of the SLN play an important role in eliciting the airway protective reflexes by irritants such as ammonia.

[An experimental study of the skin- and eye-irritating action of an artichoke preparation]

Studies for evaluation of the acute and subacute (21 day) dermal toxicity, skin-irritating, eye-irritating and skin-sensitizing effects of the preparation "Artishok" are carried out in order to determine the professional risk in direct skin contact during its production. The experiments are performed according to the Bulgarian standards and the requirements of OES. It is considered on the basis of the studies that the preparation is not able to produce dermal intoxications. The maximal single dose of 6000 mg.kg-1 is LD0. After 21 day dermal application of the preparation in doses 1000 and 3000 mg.kg-1 there are not observed any signs of intoxication, cumulative effect or changes in the integral, haematologic and biochemical studies of the white rats. These doses are considered to be inefficient. Neither skin-irritating nor eye-irritating effect has been proved. The determining of the skin-sensitizing potential of the preparation in guinea pigs through a maximizing test reveals lack of skin allergic reaction in the conditions of the experiment.

Effects of irritants on airways reactivity

The authors observed reactivity changes of airways smooth muscles after exposure of experimental animals to toluene and hyperoxia. The pretreatment with antioxidants did not prevent these changes.

Adaptive gastric mucosal cytoprotection in rats: different modes of action by three mild irritants

The mechanisms of adaptive mucosal cytoprotection by mild irritants were investigated in rats. In an ex vivo chamber preparation, application of 20% ethanol, 5% NaCl or 0.3 M HCl to the posterior side of the mucosa significantly protected that side of the stomach against mucosal damage caused by subsequent exposure to 100% ethanol, with contralateral transmission of protection to the anterior side by 20% ethanol and 0.3 M HCl. Atropine or lidocaine significantly reversed the cytoprotection of 20% ethanol. Bilateral vagotomy partially prevented the antilesion action of 20% ethanol, and completely prevented the action of 0.3 M HCl. However, the three mild irritants did not affect gastric mucosal blood flow, but restored the ion transport mechanism which was depressed by ethanol. It is therefore concluded that the three mild irritants have their own distinctive cytoprotective mechanisms against ethanol ulceration, which is predominantly not mediated by effects on the vascular system of the gastric mucosa.

Long-term lung sequelae following accidental chlorine gas exposure

Acute exposure to sublethal doses of chlorine gas resulted in persistent pulmonary symptoms in 3 patients who had no past history of respiratory disease. The patients complained of intermittent dyspnea in association with respiratory irritants and physical exertion for more than 2.5 years postexposure. Four months after the accident bronchoalveolar lavage showed an inflammatory cell reaction, whereas 16 months later the differential cytology proved nearly normal. Moderate to severe nonspecific bronchial hyperresponsiveness was assessed in intervals of 4, 20 and 30 months after the accident. All patients showed the typical features of the reactive airways dysfunction syndrome defined as an asthma-like occupational illness after an acute exposure to highly concentrated respiratory irritants. We conclude that a single high exposure to chlorine gas may lead both to acute respiratory injury and to long-term reactive airway dysfunction with typical symptoms of inflammatory changes of the airways and nonspecific bronchial hyperresponsiveness.

Brainstem neurons expressing c-Fos immunoreactivity following irritant chemical stimulation of the rat's tongue

Many chemicals including nicotine, capsaicin and piperine (pungent chemicals in red and black peppers, respectively) evoke oral pain and irritation via largely unknown neural mechanisms. As a first step in defining the central pathway for oral chemical irritation, we have used an immunohistochemical method to map locations of brainstem neurons expressing the nuclear protein, c-Fos (a putative nociceptive marker), following application of various irritants to the tongue. In barbiturate-anesthetized rats, one of the following was applied to the dorsal surface of the tongue: nicotine (0.5%), capsaicin (0.1%), histamine (2 or 20%), piperine (0.2%), acetylcholine (10%) or vehicle control (0.9% saline, dH2O, 70% ethanol). After 2 h the rat was perfused with fixative and the brainstem removed, sectioned, and processed immunohistochemically. Following application of each irritant, fos-immunoreactive nuclei were consistently observed in the superficial dorsal horn of dorsomedial trigeminal nucleus caudalis (-3 to +0.5 mm relative to obex), interstitial (paratrigeminal) nucleus, and area postrema. Approximately equal numbers were observed bilaterally even with unilateral application to the tongue. Fos-immunoreactive nuclei were observed in dorsomedial trigeminal caudalis bilaterally when a restricted area on the tip of the tongue was stimulated with capsaicin, but were located predominantly ipsilaterally following stimulation of the lateral tongue. Few or no Fos-immunoreactive nuclei were seen in these areas in control rats. Numbers of Fos-immunoreactive nuclei were significantly increased following nicotine and capsaicin in ventrolateral trigeminal nucleus caudalis and nucleus of the solitary tract. Fos-immunoreactivity was also seen consistently in the ventrolateral medulla dorsal to the lateral reticular nucleus, and vestibular and cochlear nuclei, and less consistently in nucleus raphe pallidus and inferior olive, in both irritant and in control groups, indicating that it was not stimulus-evoked. These results have identified a population of neurons in the dorsomedial trigeminal nucleus caudalis likely to be involved in signaling chemical irritation of the tongue. Increases in Fos-immunoreactivity observed in the nucleus of the solitary tract, area postrema, and ventrolateral trigeminal caudalis also suggest roles for these areas in autonomic responses consequent to oral irritation.

Adaptive cytoprotection by ammonia and urea-urease system in the rat gastric mucosa

Urease and ammonia (NH4OH) have been proposed to be play a major role in the pathogenesis of the the Helicobacter pylori (Hp)-associated gastric damage but the mechanism of this damage has not been fully explained. This study was designed the determine whether topical application with NH4OH at low concentration or the generation of the NH4OH in gastric lumen by the hydrolysis of urea in the presence of urease can induce adaptive cytoprotection. Single insult of NH4OH alone in various concentrations (15-500 mM) caused the mucosal damage starting at 30 mM and reaching at 250 mM the value similar to that obtained with 100% ethanol and being accompanied by the fall in gastric blood flow to about 30% of the normal value. When the mucosa was first exposed to the low concentration (15 mM) of NH4OH, causing by itself only small microscopic damage of surface epithelium, but then insulted by a high concentration (250 mM) of NH4OH, the extent of mucosal damage was greatly attenuated as compared to that caused by NH4OH alone. This "adaptive" cytoprotection, accompanied by the rise in the GBF, was reversed in part, after the pretreatment with indomethacin to inhibit PG-cyclooxygenase, with L-NAME to suppress NO-synthase or with capsaicin to induce deactivation of sensory nerves. The combined topical pretreatment with urea (2%) and urease (100 U) to generate NH4OH in the stomach, also significantly reduced the severity of gastric lesions induced by 100% ethanol and this was also accompanied by a significant rise in the gastric blood flow. The protective and hyperemic effects of urea and urease were significantly attenuated by the pretreatment with indomethacin or suppression of NO-synthase by L-NAME. The functional ablation of sensory nerves by the pretreatment with capsaicin also reversed, in part, the protective effect of the combination of urea plus urease and abolished completely the mucosal hyperemia accompanying this protection. We conclude that 1) NH4OH alone at higher concentrations damages the gastric mucosa but when applied at lower concentration corresponding to that in the stomach of Hp-infected patients, or generated by the urea in the presence of urease, NH4OH acts like "mild irritant" to induce adaptive cytoprotection, 2) this adaptive cytoprotection is mediated, in part, by endogenous PG, sensory nerves and arginine-NO-dependent pathway.