Rate constant for the H˙ + H2O → ˙OH + H2 reaction at elevated temperatures measured by pulse radiolysis

Maintaining the structural integrity of materials in nuclear power plants is an essential issue associated with safe operation. Hydrogen (H₂) addition or injection to coolants is a powerful technique that has been widely applied such that the reducing conditions in the coolant water avoid corrosion and stress corrosion cracking (SCC). Because the radiation-induced reaction of ˙OH + H₂ → H˙ + H₂O plays a crucial role in these systems, the rate constant has been measured at operation temperatures of the reactors (285-300 °C) by pulse radiolysis, generating sufficient data for analysis. The reverse reaction H˙ + H₂O → ˙OH + H₂ is negligibly slow at ambient temperature; however, it accelerates considerably quickly at elevated temperatures. Although the reverse reaction reduces the effectiveness of H₂ addition, reliable rate constants have not yet been measured. In this study, the rate constants have been determined in a temperature range of 250-350 °C by pulse radiolysis in an aqueous I^- solution.

Sequential radiation chemical reactions in aqueous bromide solutions: pulse radiolysis experiment and spur model simulation

Pulse radiolysis experiments were carried out to observe transient absorptions of reaction intermediates produced in N₂O- and Ar-saturated aqueous solutions containing 0.9–900 mM NaBr.

Temperature and density effects on the absorption maximum of solvated electrons in sub- and super-critical methanol

The optical absorption spectra of the solvated electron ([Formula: see text]) in sub- and super-critical methanol are measured by both electron pulse radiolysis and laser photolysis techniques, at temperatures in the range 220–270 °C. Over the density range studied (~0.45–0.59 g/cm3), the position of the absorption maximum ([Formula: see text]) of [Formula: see text] is found to shift only slightly to the red with decreasing density. In agreement with our previous work in water, at a fixed pressure, [Formula: see text] decreases monotonically with increasing temperature in passing through the phase transition at Tc (239.5 °C). By contrast, at a fixed density, [Formula: see text] exhibits a minimum as the solvent passes above the critical point into the supercritical state. These behaviors are discussed in terms of microscopic arguments based on the changes that occur in the methanol properties and methanol structure in the sub- and super-critical regimes. The effect of the addition of a small amount of water to the alcohol on the optical absorption energy of [Formula: see text] is also investigated.

Radiolytic formation of Tc(IV) oxide colloids

Technetium(IV) oxide colloids were radiolytically formed by γ irradiation of aqueous solutions of pertechnetate (TcO4−). Pertechnetate solutions (5.5×10−5-2.9×10−4M) were irradiated with bremsstrahlung from an electron linear accelerator at 40 and 17 °C. The color of irradiated solutions gradually changed to brownish black, suggesting the formation of Tc(IV) oxide colloids (TcO2·nH2O). A transmission electron microscopy (TEM) analysis showed that the size of colloids distributed around 30 to 130 nm in diameter. The characteristic X-rays from technetium and oxygen were simultaneously detected from colloid particles at the TEM measurements. Round-shaped colloids were produced by irradiation at 40 °C, whereas irregular-shaped colloid particles composed of tiny particles (2 nm in diameter) were produced at 17 °C. The concentration of TcO4−in the target solution gradually decreased with an increase of the absorbed dose, corresponding to an increase of the colloid yield. The yield of colloids sharply increased in the solution deaerated by Ar bubbling before irradiation, but strongly suppressed in the solution saturated with oxygen (O2) or nitrous oxide (N2O) gas. The fact suggests that hydrated electrons play an important role in the course of the reduction of TcO4−and that Tc(IV) oxide colloids were formedviasuccessive disproportionation reactions of Tc(VI) and Tc(V). The formation mechanisms of Tc(IV) oxide colloids are discussed.

Evaluation of CD86 expression and MHC class II molecule internalization in THP-1 human monocyte cells as predictive endpoints for contact sensitizers

The aim of this study was to explore the usefulness of a human monocyte cell line in the development of in vitro models for predictive testing of contact sensitizers. Several studies have shown that contact sensitizers induce CD86 expression and enhanced internalization of MHC class II molecules in dendritic cells (DCs). We used THP-1, a human monocyte cell line, as a replacement for DCs for evaluation of these phenotypical alterations as predictive endpoints for contact sensitizers. Known sensitizers and irritants were evaluated. After 24-h exposure to samples, the expression of CD86 on THP-1 cells was measured by flow cytometry. Sensitizers such as dinitrochlorobenzene (DNCB), 2-mercaptobenzothiazole (MBT), eugenol, p-phenylenediamine (PPDA) and ammonium tetrachloroplatinate (Pt) enhanced CD86 expression on THP-1 cells, while nickel sulfate, cobalt sulfate and irritants such as methylsalicylate (MS), sodium dodecyl sulfate (SDS) and dimethyl sulfoxide (DMSO) did not augment CD86 expression. A synergistic effect was observed when DNCB and IFN-alpha were added simultaneously to a culture of THP-1 cells. Furthermore, internalization of MHC class II molecules was observed when the cells were treated with some of sensitizers for 2 h. The inducing effects of chemicals on the two phenotypical alterations were the same. These results suggest that these test systems can be used to predict contact-sensitizing ability of chemicals as an in vitro sensitization assay.

Modified short-term guinea pig sensitization tests for detecting contact allergens as an alternative to the conventional test

The conventional adjuvant and patch test (APT) method of guinea pig sensitization testing was modified in 2 ways, s-APT and s-APT(2), in order to shorten the test period. These short-term test methods consist of 72-h closed application of test material with intradermal injection of emulsified Freund's complete adjuvant (E-FCA) for 1st induction, 48-h closed application of test material with (s-APT) or without (s-APT(2)) intradermal injection of E-FCA on the 7th day for 2nd induction, and open application on the 14th day for challenge. They were compared with conventional APT by using 8 allergenic chemicals (formaldehyde, nickel sulfate, cobalt sulfate, ethyl-p-aminobenzoate (benzocaine), isoeugenol, 2-mercaptobenzothiazole, 2,4-dinitrochlorobenzene (DNCB) and 1-phenylazo-2-naphthol (Sudan I)). The short-term methods gave similar results to those of conventional APT in terms of mean response, sensitization rate and sensitization potency (challenge concentration that induces a mean response equal to 1.0). Thus, our short-term methods, which are capable of evaluating skin sensitization within 17 days, are sufficiently sensitive to detect potentially hazardous contact allergens.

Induction of unscheduled DNA synthesis in hairless mouse epidermis by 8-methoxypsoralen plus ultraviolet A (PUVA)

Induction of unscheduled DNA synthesis (UDS) by 8-methoxypsoralen (8-MOP) plus ultraviolet A (UV-A) (PUVA) was investigated in the epidermis of female hairless mice by means of an in vivo--in vitro assay using a liquid scintillation counting method. Groups of three to five 8-week-old female hairless mice had 8-MOP applied once onto two areas of the back after stripping of the stratum corneum with adhesive tape to enhance skin penetration, and were irradiated with UV-A. Skin samples were taken and cultured in a medium containing [3H]thymidine with or without hydroxyurea (HU) for 2 hr. DNA of the epidermis was extracted, and the incorporation of [3H]thymidine into DNA and the DNA content were determined with a liquid scintillation counter and a fluorescence spectrophotometer, respectively. Induction of UDS was judged in terms of the UDS index [(the ratio of DNA synthesis in the presence of HU to that in its absence) x 100]. In a time-course study, the UDS index was increased at 1, 2 and 24 hr after 1 x 10(5) J/m2 UV-A irradiation with 0.001% 8-MOP, reaching the maximum level at 24 hr. In a dose-response study, it was significantly increased at the dose of 1 x 10(5) J/m2 of UV-A at 24 hr with 0.001% 8-MOP, but showed no significant change at the doses of 0.5 x 10(5), 2 x 10(5) and 4 x 10(5) J/m2. In a further study on the effect of varying the dose of 8-MOP, the UDS index was significantly increased at 0.001 and 0.002% 8-MOP at 24 hr after 1 x 10(5) J/m2 UV-A irradiation, reaching the maximum level with 0.002% 8-MOP. The increase of the UDS index in these studies was less than 3-fold. These results show that PUVA causes a small induction of UDS, which might be due to slow DNA excision repair over a long period.

Effect of aging on unscheduled DNA synthesis induction by UV-B irradiation in hairless mouse epidermis

Age-related induction of unscheduled DNA synthesis (UDS) by ultraviolet B (UV-B) irradiation was investigated in the epidermis of female hairless mice by means of an in vivo--in vitro assay using a liquid scintillation counting method. Skin samples were taken and cultured in a medium containing [3H]thymidine with or without hydroxyurea (HU) for 2 hr. DNA of the epidermis was extracted, and the incorporation of [3H]thymidine into DNA and the DNA content were determined with a liquid scintillation counter and a fluorescence spectrophotometer, respectively. Induction of UDS by UV-B was judged in terms of the value of the UDS index calculated as a percentage of the respective unexposed control value taken as 100% [the UDS index is given by (the ratio of DNA synthesis in the presence of HU to that in its absence) x 100]. DNA synthesis both in the presence and absence of HU decreased with age [12 months old (M) < 8 M < 4 M < 2 M < 1 M)], concomitantly with a small but significant increase of UDS index. The decrease was high in the younger age groups and moderate in the older age groups. UV-B increased the UDS index approximately 14-, 12- and 9-fold at 1 hr after 1,000 J/m2 irradiation in 1 M, 2 M and 12 M mice, respectively, and these increases were partly reversed at 4 hr after irradiation. UV-B also increased the UDS index approximately 25-, 24- and 21-fold at 1 hr after 4,000 J/m2 irradiation for each age group. However, there was no statistically significant age-related difference in the magnitude of the UDS index after irradiation of UV-B. These results show that replicative DNA synthesis decreases with age, whereas DNA repair capacity after UV-B irradiation does not change with age under these conditions.

Effect of the photocatalytic activity of TiO(2) on plasmid DNA

We investigated the photodynamic DNA strand-breaking activity of TiO(2). A solution of super-coiled pBR 322 DNA was irradiated with 5 J/cm(2) of UVA in the presence of TiO(2) and the products were analyzed by using gel electrophoresis. The ratio of open-circular DNA to super-coiled circular DNA was calculated from the resulting peak areas as a DNA strand-breaking index (SBI). The SBI of anatase-structure TiO(2) (band gap=3.23 eV) was greater than that of rutile structure (band gap=3.06 eV), and the level of SBI correlated with the photocatalytic activity for degradation of 2-propanol. The inhibitory effects of active oxygen scavengers, including DMSO, glutathione and histidine, on the DNA strand-breaking activity were examined. All of the scavengers except ascorbic acid showed inhibitory effects, as did several polyhydric alcohols including mannitol, a well-known hydroxyl radical scavenger. These results suggest that the photodynamic DNA strand-breaking activity of TiO(2) is due to active oxygen species, especially hydroxyl radicals. Polyhydric alcohols showed an inverse correlation between the inhibitory effect on DNA strand-breaking activity and the octanol/water partition coefficient (logP).

Induction of unscheduled DNA synthesis in hairless mouse epidermis by ultraviolet light

The activity of ultraviolet (UV) light to induce unscheduled DNA synthesis (UDS) was investigated in hairless mouse epidermis by means of an in vivo-in vitro assay using a liquid scintillation counting method. Groups of three to five 8-week-old female hairless mice were irradiated with UV-B or UV-A, then skin samples were taken and cultured individually in medium containing [3H]thymidine with or without hydroxyurea (HU) for 2 hr. DNA of the epidermis was extracted, and incorporation of [3H]thymidine and the DNA content were determined with a liquid scintillation counter and a fluorescence spectrophotometer, respectively. Induction of UDS was judged in terms of the UDS index [(the ratio of DNA synthesis in the presence of HU to that in its absence) x 100]. UV-B increased the UDS index 1 hr after irradiation of 500 J/m2, which corresponds to approximately 1 minimal erythema dose or 1 minimal edema dose, and showed a dose-dependent increase up to 17-fold in the UDS index at irradiation doses of 500 to 2,000 J/m2. In a time-course study, UV-B also increased replicative DNA synthesis (RDS) 48 hr after irradiation at 1,000 J/m2. On the other hand, UV-A did not increase the UDS index at irradiation doses of 2 x 10(5) to 8 x 10(5) J/m2. These results show that induction of UDS by UV irradiation depends on wavelength and an increase of RDS in the epidermis exposed to UV-B irradiation appears after induction of UDS.

Interaction of hydrated electron with dietary flavonoids and phenolic acids: rate constants and transient spectra studied by pulse radiolysis

The reaction rate constants and transient spectra of 11 flavonoids and 4 phenolic acids reacting with e(aq)- at neutral pH were measured. Absorption bands of the transients of e(aq)- reacting with the above compounds all located at a wavelength shorter than 400 nm. The e(aq)- scavenging abilities were divided into three groups: (+)catechin ((1.2 +/-0.1) x 10(8) M(-1)s(-1)) < 4-chromanol ((4.4 +/- 0.4) x 10(8) M(-1)s(-1)) < genistein ((6.2+/-0.4) x 10(9) M (-1) s(-1) approximately genistin ((8 +/- 1) x 10(9) M(-1)s(-1)) approximately rutin ((7.6 +/- 0.4) x M(-1)s(-1) approximately caffeic acid ((8.3 +/- 0.5) x 10(9)M(-1)s(-1)) < transcinnamic acid((1.1 +/- 0.1) x 10(10) M(-1)s(-1)) approximately p-coumaric acid ((1.1 +/- 0.1) x 10(10) M(-1)s(-1) approximately 2,4,6-trihydroxylbenzoic acid((1.1 +/- 0.1) x 10(10) M(-1)s(-1)) approximately baicalein ((1.1 +/- 0.5) x 10(10) M(-1)s(-1)) approximately baicalin((1.3 + 0.1) X 10(10) M(-1)s(-1)) approximately naringenin ((1.2 +/- 0.1) x 10(10) M(-1)s(-1)) approximately naringin ((1.0 +/- 0.1) x 10(10) M(-1)s(-1)) approximately gossypin((1.2 +/- 0.1) x 10(10) M(-1)s(-1)) approximately quercetin((1.3 +/- 0.5) x 10(10) M(-1)s(-1)). These results suggested that C4 keto group is the active site for e(aq)- to attack on flavonoids and phenolic acids, whereas the o-dihydroxy structure in B ring, the C2,3 double bond, the C3-OH group, and glucosylation, which are key structures that influence the antioxidant activities of flavonoids and phenolic acids, have little effects on the e(aq)- scavenging activities.

[Constriction of liver tissue herniated through a diaphragmatic defect, simulating a pulmonary tumor]

Defects in the dome of the right diaphragm are a rarity among diaphragmatic abnormalities. Here we report the case of an elderly man who presented with an intrathoracic nodular opacity adjacent to the right diaphragm on chest radiographs. A radionuclide liver scan and maximum intensity projection (MIP) images of a computed tomographic (CT) scan together yielded a diagnosis of diaphragmatic defect with herniation of liver tissue. The herniated liver was so constricted that the angle made by the nodule and diaphragm became acute, resulting in close resemblance to a pulmonary tumor. This unusual configuration of herniated liver tissue was reviewed and the cause of constriction and diagnostic procedure were discussed. To avoid unnecessary examinations, herniation of liver tissue should be included in the differential diagnosis of intrathoracic nodular opacities, particularly when they are in contact with the diaphragm.

Association between pulmonary microthromboembolism and coagulation variables in hypercoagulable states: an autopsy study

OBJECTIVE

This autopsy study was carried out to investigate the relationship between the number of pulmonary microthromboemboli and coagulation tests in patients with coagulation abnormalities.

METHODOLOGY

Fifty-one patients in whom coagulation studies were performed within 2 days prior to death were studied. The coagulation tests included platelet counts, prothrombin times expressed as International Normalized Ratios (INR), activated partial thromboplastin times, fibrinogen concentrations, plasma fibrinogen/fibrin fragment E antigen levels, and plasma D-dimer levels. For microscopic analysis, five tissue blocks of the lung were taken from each subject and the number of pulmonary microthromboemboli per 20 cm2 of tissue sections was calculated.

RESULTS

Thirty-six of the 51 patients had pulmonary microthromboembolism. International Normalized Ratios were higher than 1.7 in 12 of 36 embolic and in two of 15 non-embolic patients (33.3% of sensitivity and 86.7% of specificity). There was no significant difference in D-dimer levels between the two groups. Multiple regression analysis identified that INR was significantly related to the number of microthromboemboli (P = 0.042).

CONCLUSIONS

D-dimer levels appear to be inappropriate as a single screening test for disseminated intravascular coagulation (DIC) in critically ill patients because the levels in these subjects are elevated irrespective of the presence of microthromboemboli. Because of the high specificity, INR could be a specific marker for microthromboemboli. The significant association between the number of microthromboemboli and INR might indicate the importance of the extrinsic pathway in the initiation of DIC.

Induction of unscheduled DNA synthesis in hairless mouse epidermis by skin carcinogens

Induction of unscheduled DNA synthesis (UDS) in hairless mouse epidermis by six chemicals was determined in an in vivo-in vitro assay by using a liquid scintillation counting method. Test chemicals were applied once onto two areas of the back of female hairless mice after stripping of the stratum corneum with adhesive tape to enhance skin penetration. After exposure, the skin samples were taken and cultured in a medium containing [3H]thymidine with or without hydroxyurea (HU, an inhibitor of replicative DNA synthesis). DNA of the epidermis was extracted, and incorporation of [3H]thymidine into DNA and the DNA content was determined with a liquid scintillation counter and a fluorescence spectrophotometer, respectively. Induction of UDS by chemicals was judged by calculation of the UDS index [(the ratio of DNA synthesis in the presence of HU to that in its absence) x 100]. A good correlation between UDS induction and organ specificity of carcinogens was observed. 4-Nitroquinoline 1-oxide, a skin carcinogen used as a positive control, induced a dose-dependent increase in the UDS index of approximately 12-fold at 2 hr after exposure, while 1,2-epoxydodecane, a non-skin carcinogen applied as a negative control, did not increase the UDS index. Four other skin carcinogens induced dose-dependent increases in the UDS index; N-methyl-N'-nitro-N-nitrosoguanidine and diepoxybutane at 2 hr after exposure, and 7,12-dimethylbenz[a]anthracene and benzo[a]pyrene at 24 hr after exposure. The results suggest that UDS is a good marker of the genotoxicity of skin carcinogens.

Correlation between clinical and pathological features of pulmonary thromboemboli and the development of infarcts

Factors that predispose pulmonary thromboembolism to infarction have not been completely understood. The present autopsy study was carried out to evaluate these factors both clinically and pathologically. Between 36 subjects with pulmonary infarction and 33 individuals who had multiple pulmonary thromboembolism but no infarction, clinical and pathological features including congestive heart failure (CHF), shock, sepsis, neoplasm, emphysema, pneumonia, the amount of pleural effusion, diameter of occluded arteries, and segmental and dimensional location of thromboemboli were compared. Multiple regression analysis revealed that clinically CHF was significantly associated with the development of infarction. In pathological factors, thromboemboli located in the distal artery and in the lower lobe were significantly associated with infarction. The size of the infarcts was small and all the complete infarcts were in contact with the pleura. In addition to CHF, occlusion of small arteries in the lower lobe and near the pleura seems to be associated with the occurrence of infarction.

Pneumococcal spherical pneumonia multiply distributed in one lung

Spherical pneumonia, which is seen more frequently in children than in adults, is usually manifested as a solitary nodule. We report the case of a middle-aged man with small spherical pneumonia, with multiple distribution in the right lung, caused by Streptococcus pneumoniae. This type of pneumonia is very unusual and should be included in the differential diagnosis of multiple nodular densities of the lung.

Evaluation of human skin irritation by carboxylic acids, alcohols, esters and aldehydes, with nitrocellulose-replica method and closed patch testing

Closed patch testing and the nitrocellulose-replica method are performed as useful clinical methods for the evaluation of human skin irritation by cosmetics and topical medicaments. Comparison of the sensitivity between microscopic scoring by nitrocellulose-replica method and visual scoring by closed patch test in the detection of skin irritation, however, has not been well studied with statistical analysis. Here, we evaluated human skin irritation by carboxylic acids, alcohols, esters and aldehydes, with different chain length (C8-C18), using both methods. The results of closed patch testing showed that, although the score of skin irritation for carboxylic acids (C8, C12), alcohols (C8) and aldehydes (C8), tested at a concentration of 0.5 m-2.0 m, significantly increased with increasing concentration of the test compounds, ester compounds scarcely caused any irritation on the surface of the skin occluded. In addition, an increase of carbon chain length in the test compounds made it impossible to detect skin irritation. In contrast, the nitrocellulose-replica method could evaluate skin reactions against very weak irritants that gave no macroscopic alterations on the skin surface in the closed patch test. However, the scoring system is somewhat subjective and should be improved to make the analysis more objective.

A modification of the local lymph node assay for contact allergenicity screening: measurement of interleukin-2 as an alternative to radioisotope-dependent proliferation assay

The local lymph node assay is an effective prediction method for contact allergenicity, but employs radioisotopes. We investigated whether measurement of interleukin-2 (IL-2) production by lymph node cells could be used instead to predict contact allergenicity of chemicals. Test chemicals were applied for three consecutive days to both ears of Balb/c mice and the auricular lymph nodes were obtained on either the fourth or fifth day after the first application. Both IL-2 concentration in supernatant of the suspension and proliferative activity of lymph node cells were determined after 24-, 48-, 72-h cell culture in RPMI-1640 medium by ELISA and by measuring [3H]methylthymidine incorporation, respectively. These two methods detected allergenicity similarly except in the case of TNCB and oxazolone, which showed excessive proliferation-inducing capacity as compared to IL-2 release-increasing effect. Flow cytometry showed that these two chemicals also increased the percentage of Iad-positive cells in the lymph nodes, suggesting that these chemicals might induce not only cellular immunity but also humoral immunity. We conclude that interleukin-2 assay is a convenient and dependable method for screening strong contact allergens without using radioisotopes.

Incidence of pulmonary thromboembolism, infarction and haemorrhage in disseminated intravascular coagulation: a necroscopic analysis

BACKGROUND

The pathological features of the lung in disseminated intravascular coagulation (DIC) have not been established. This study was carried out on lungs taken at necropsy to examine the incidence and extent of thromboembolism, infarction, and haemorrhage.

METHODS

The subjects were 87 patients whose illnesses were complicated by DIC and 64 patients who showed no abnormalities of blood coagulation in their terminal illness. The lungs were fixed by intrabronchial infusion of 10% formalin, cut into 5 mm thick slices, and each cut surface was carefully examined for macroscopic thromboembolism, infarction, and haemorrhage. Five tissue blocks per case were taken for quantitative analysis of microscopic thromboembolism.

RESULTS

In the control group macroscopic thromboembolism was identified in 20 cases (31.3%), infarction in one, and haemorrhage also in one. Moreover, fibrin thrombosis was seen in 13 cases (20.3%) and microthromboembolism in 24 (37.5%). Of the 87 patients with DIC, thromboembolism was found in 51 cases (58.6%), infarction in six, haemorrhage in 14, microscopic fibrin thrombosis in 43 (49.4%), and microthromboembolism in 45 (51.7%). Macroscopic thromboembolism, haemorrhage, and fibrin thrombosis were found more often in the patients with DIC.

CONCLUSIONS

In addition to fibrin thrombosis, macroscopic thromboembolism and haemorrhage were the main pathological findings in the lungs of patients dying with DIC. The frequency of pulmonary infarction increased in proportion to the frequency of thromboembolism.

[A case of primary anterior mediastinal choriocarcinoma]

A 25-year-old man was admitted to our hospital because of hemosputum and abnormal shadows on chest X-ray film. The chest film showed a mass shadow located in the right hilum and multiple coin lesions in bilateral lung fields. The chest CT scan showed a bulky mass sized 7 cm X 6 cm at the anterior mediastinum. This case was suspected to be choriocarcinoma because he was young, it was rapidly progressive and also because serum LDH and beta-HCG values were raised. The specimens obtained by surgical biopsy showed HCG-stain positive syncytiotrophoblasts. Cancer chemotherapy was started with CDDP and other anti-cancer drugs, but he succumbed about 3 months after admission. Autopsy findings showed no scar formation of his testes, and the primary lesion was finally diagnosed to be in the anterior mediastinum. Extra-gonadal choriocarcinoma is rare, and beta-HCG is very useful for its diagnosis and the follow-up of the clinical course.

Persistent light reaction: induction in the guinea pig

Persistent light reactions similar to those in humans were observed in the study of photoallergenicity of chemicals in guinea pigs. The animals photoinduced with chemicals reacted to long-wavelength ultraviolet (UVA) radiation in the absence of test materials at the challenge stage. The sensitivity of the animals to UVA persisted for more than 1 year. The minimum erythema dose to UVB of animals in the treated group was less than that in the control group. Our investigations indicate that the main factors influencing the elicitation of persistent light reaction were the amount of Freund's complete adjuvant (FCA) used to enhance the allergic response in animals, and the UVA dose at the induction stage. Based on these findings, we have developed a method to make animals persistent light reactors with high frequency. This method consists of 1 intradermal injection of 1.2 ml emulsified FCA, 5 irradiations with 20.4 J/cm2 of UVA, and topical applications of 5% p-aminoethylbenzoate (benzocaine) at the induction stage. We also found that photosensitivity could be induced using FCA and UVA without photosensitizers.

Mechanism for 6-methylcoumarin photoallergenicity

6-Methylcoumarin (6-MC), a synthetic fragrance material, has been reported to be photoallergenic both in man and in guinea pigs. To elucidate the possible mechanism of photoallergenicity, 6-MC in ethanolic solution was exposed to 200 joules/cm2 of long-wavelength ultraviolet (UV) ranging from 320 to 400 nm for 16 hr, and was examined for its contact allergenicity by means of a modified guinea pig maximization test. Strong allergic responses were observed, indicating that UV plays a catalytic role in forming contact allergens during irradiation. The solution was fractionated to isolate and purify contact sensitizers by gel-permeation chromatography and high-performance liquid chromatography. By employing mass spectrometry and proton and carbon-13 nuclear magnetic resonance, mono- and diethyl esters of 6-MC dimer were compounds identified which showed allergic reactions in guinea pigs sensitized with UV-irradiated 6-MC.

A modified technique of guinea pig testing to identify delayed hypersensitivity allergens

A modified guinea pig testing technique was developed for the detection of weak allergens and allergenicity of materials unsuitable for testing by intradermal injection. This test involved the use of Freund's complete adjuvant to stimulate the immune system of the animal, and external application instead of intradermal injection of the test compound in the induction stage. The allergenicity of Sudan III, Brilliant Lake Red R and Sudan I was tested by this procedure. In the dose-effect study of Sudan I, the dose dependency of a positive reaction of the induction and challenge concentrations was recognized. The test was compared with three other guinea pig sensitization tests. The results obtained with this test correlated well with those obtained with the guinea pig maximization test.