Role of Hypobaria in Fluid Balance Response to Hypoxia

To estimate the separate and combined effects of reduced P(B) and O2 levels on body fluid balance and regulating hormones, measurements were made during reduced PB (altitude, ALT; P(B) = 432 mm Hg, F(I(O2)) = 0.207), reduced inspired O2 concentration (normobaric hypoxia, HYX; P(B) = 614 mm Hg, F(I(O2)) = 0.142), and lowered ambient pressure without hypoxia (normoxic hypobaria HYB; P(B) = 434 mm Hg, F(I(O2)) = 0.296). Nine fit and healthy young men were exposed to these conditions for 10 h in a decompression chamber. Lake Louise AMS scores, urine collections, and blood samples were obtained every 3 h, with recovery measurements 2 h after exposure. AMS was significantly greater during ALT than HYX, as previously reported (J. Appl. Physiol. 81:1908-1910. 1996), because the combination of reduced P(B) and P(O2) over the 10 h favored fluid retention by reducing urine volume, while plasma volume (PV) remained higher than during HYX. At ALT the plasma Na+ fell significantly at 6 h, probably from dilution of extracellular fluid, and antidiuretic hormone (ADH) was highest (p = 0.006 versus HYB). The PV, urine flow, free water clearance, and plasma renin activity (PRA) rose significantly during recovery from ALT as AMS symptoms subsided, suggesting increased intravascular fluid and reduced adrenergic tone. During HYB, the plasma aldosterone (ALDO) and K+ levels were significantly elevated, and PRA was highest and ADH lowest, without fluid retention. During HYX, fluid balance was similar to HYB, but PV and ALDO were significantly lower, and ALDO increased significantly in recovery from HYX. The fluid retention at ALT in AMS-susceptible subjects appears related to a synergistic interaction involving reduced P(B) and ADH and ALDO.

Use of the mouse intranasal test (MINT) to determine the allergenic potency of detergent enzymes: comparison to the guinea pig intratracheal (GPIT) test

A mouse intranasal test (MINT) was developed to determine the relative allergenicity of detergent enzymes. In this simple method, various doses of the enzymes are administered in a detergent matrix, via intranasal instillation, on days 1, 3, and 10, with serum samples collected on day 15. The sera are then analyzed for enzyme specific IgG1 antibody by an antigen specific enzyme immunoassay. The protease enzyme Alcalase (protease Subtilisin Carlsberg) has been used as a benchmark enzyme for development and characterization of the model. The objective of the current studies was to obtain potency comparisons with other protease and nonprotease enzymes and to begin to assess the validity of the model by comparison with potency determinations obtained with the guinea pig intratracheal (GPIT) test. The range of potencies detected among several enzymes of different classes was approximately 60-fold (compared with Alcalase). Modification of the dosing regimen to permit slightly more extended dosing did not change the relative potency determination. Comparison of data from the MINT and GPIT methods indicate that both the mouse and the guinea pig recognize the bacterial amylase Termamyl and a fungal exocellulase as more potent than Alcalase, a serine protease (Subtilisin B) and a fungal alpha-amylase (Fungamyl) as less potent than Alcalase, and the serine protease, Savinase, as equivalent to Alcalase. Also, these data are in alignment with clinical data on the prevalence of occupational enzyme sensitization. Given the simplicity and low cost of the MINT method compared with the GPIT test, these results support continued development of the method as an alternative approach for assessing the allergenicity of enzymes.

Proteolytic detergent enzymes enhance the allergic antibody responses of guinea pigs to nonproteolytic detergent enzymes in a mixture: implications for occupational exposure

A guinea pig intratracheal test was developed to assess the respiratory allergenicity of enzymes used in the detergent industry. Information gained from this test was used in a process for setting operational exposure guidelines to protect worker health. Mixtures of enzyme proteins were given to guinea pigs once per week for 10 weeks to determine whether there were interactions among enzymes that affected the induction of antibody responses to each enzyme in the mixture. Passive cutaneous anaphylaxis antibody titers against each enzyme were measured in sera. Mixtures of two or three enzymes always consisted of a protease (Alcalase, Savinase; Novo Industri A/S) with an alpha-amylase (Termamyl; Novo Industri A/S), a lipase (Lipolase; Novo Industri A/S), or both. Control animals were exposed to single enzymes. The antibody titers to Termamyl and Lipolase were significantly greater in animals dosed with the protease-containing mixtures as compared with control animals dosed with a single enzyme. Antibody titers to the protease were unchanged in the presence of additional enzymes in the mixture. Complete inactivation of protease activity abrogated the enhanced antibody response to Lipolase. Inhalation exposure of guinea pigs to a mixture of Alcalase and Lipolase also resulted in higher antibody titers to Lipolase as compared with animals exposed by inhalation to Lipolase alone, showing that the enhanced response was not due to intratracheal delivery of antigen to the respiratory tract. These results show that proteolytic enzymes in a mixture enhance antibody responses to other enzymes. This should be considered when defining exposure guidelines for protease-containing enzyme mixtures.

Respiratory allergenicity of detergent enzymes in the guinea pig intratracheal test: association with sensitization of occupationally exposed individuals

A guinea pig intratracheal test was used to set occupational operating guidelines for new enzyme proteins used in the detergent industry. In these studies, animals were intratracheally dosed with different levels of enzyme protein and sera from the animals were titered for allergic antibody to the enzyme. The amount of antibody produced to an enzyme was compared to the amount of antibody produced to the same protein doses of Alcalase, for which effective operating guidelines exist. These comparisons were used to determine if a new enzyme was more potent, less potent, or equivalent to Alcalase; operating guidelines were then established for the new enzyme. Termamyl was about 10-fold more potent than Alcalase and the protease subtilisin B was shown to be less potent. Another protease, Savinase, was shown to be equivalent in potency to Alcalase. The operating guidelines for Termamyl were adjusted lower, whereas the operating guidelines for the proteases were set the same as that of Alcalase. Under these conditions, we would predict that sensitizations to new enzymes would be comparable to or lower than the sensitizations to Alcalase. Prospective evaluation of skin prick test data of factory workers showed that sensitizations to Termamyl and Savinase were similar to sensitizations to Alcalase. The sensitizations to subtilisin B were lower than those to Alcalase. During this time period (7 years), only three respiratory incidents (rhinitis) were reported, demonstrating that employees with positive skin prick tests can continue to work. These comparisons indicate that the guinea pig intratracheal test is a good animal model for evaluating enzymes as respiratory allergens and that the data generated can be used to set operating guidelines for occupational allergens.

Optimization and validation of an ELISA to measure specific guinea pig IgG1 antibody as an alternative to the in vivo passive cutaneous anaphylaxis assay

Assessment of the allergenic potency of enzymes involves the use of a guinea pig model in which specific IgG1 antibody titers are used as the endpoint. The in vivo passive cutaneous anaphylaxis (PCA) assay is used to measure specific IgG1 antibody. This report describes the development and validation of an enzyme-linked immunosorbent assay (ELISA) to measure guinea pig specific IgG1 antibody as an in vitro alternative to the PCA assay. Cross reactivity of various rabbit and mouse (monoclonal) anti-guinea pig IgG1 preparations were evaluated using purified IgG1 and IgG2 from serum of guinea pigs immunized with ovalbumin. The two subclasses of guinea pig IgG were purified by first using Protein A affinity chromatography, followed by anion exchange chromatography and fluid phase isoelectric focusing. Affinity-purified rabbit anti-guinea pig IgG1 was shown to have minimal cross reactivity toward IgG2, while providing a strong signal with IgG1. The ELISA was designed as an antigen capture system in which the following are added in sequence: (1) enzyme antigen (passively adsorbed to the plate), (2) diluted serum samples from guinea pigs immunized with enzyme, (3) affinity-purified rabbit anti-guinea pig IgG1, (4) alkaline phosphatase-conjugated donkey anti-rabbit IgG, and (5) p-nitrophenyl phosphate substrate. Three replicate ELISA and PCA analyses were conducted on sera samples of varying titers from guinea pigs immunized with either Alcalase (protease), BPN' (protease), and Termamyl (amylase) enzyme. The correlation coefficients (r2) between the ELISA and PCA assay for Alcalase, BPN', and Termamyl were 0.826, 0.945, and 0.755, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between whole blood base excess and CO2 content in vivo

Empirical relationships are demonstrated for whole blood base excess (BE) and CO2 content (CCO2), both calculated from in vivo measurements of PCO2, pH, hemoglobin concentration and O2 saturation. Comparisons are provided by measurements from three separate studies: (1) supine exercise (arterial and mixed venous samples); (2) chronic obstructive disease patients (arterial samples) breathing air and 100% O2; and (3) maximal seated exercise on a bicycle ergometer with and without added inspired CO2 (arterial samples before, during and after). Two standardized values of CCO2 (vol.%) are derived which closely relate to BE (mmol/l). The CCO2 at a PCO2 of 40 mmHG [CCO2(40)] for all samples (n = 220) demonstrated a curvilinear relationship: CCO2 (40) = 45.37 + 1.48(BE) + 0.0156(BE)2, r = + 0.996, SEE = 0.88 vol.%. The CCO2 at a pH of 7.4 [CCO2(7.4)] gave a linear relationship: CCO2(7.4) = 45.09 + 2.58(BE), r = + 0.998, SEE = 1.19 vol.%. Empirical computations for the Haldane factor from studies 1 and 2 gave values of 0.285 in terms of CCO2 (vol.%/vol.%) and 0.266 for BE (mmol/l/mmol reduced Hb). The BE values can serve as useful estimates of lactate concentrations during exercise and the excellent relationships between standardized CCO2 and BE demonstrate their equivalency and either can be utilized, depending on whether quantification of the CO2 dissociation curve or acid-base status is desired.

Respiratory and immunological responses of guinea pigs to enzyme-containing detergents: a comparison of intratracheal and inhalation modes of exposure

Guinea pigs were exposed once a week for 10 weeks by intratracheal exposure to solutions of 3, 1, 0.3, or 0.1 micrograms of the enzyme protein, Subtilisn Carlsberg (Alcalase), in 250 micrograms of a detergent base. Other groups of guinea pigs were exposed by inhalation (6 hr per day, 4 days a week) to 1 mg/m3 of the aerosolized detergent base containing either 3.5, 1.1, 0.3, or 0.1% Alcalase protein. Evaluations of gross respiratory responses immediately following each intratracheal exposure revealed a significant dose response in respiratory symptoms measurable after the fourth exposure and continuing throughout the study. In the inhalation experiment, during Weeks 4 through 10, animals were observed to have respiratory symptoms which were dependent upon both the dose of enzyme and on total exposure to the enzyme/detergent atmosphere. For both intratracheal and inhalation routes of exposure, the initial appearance of respiratory symptoms coincided with the first appearance of measurable serum allergic antibodies specific to Alcalase. The allergic antibody levels increased with time and dosage by both routes of exposure, and the antibody titers generated by the intratracheal administration of antigen were comparable to those generated by the inhalation route of exposure. These results indicate that the intratracheal technique is appropriate for the evaluation of the respiratory allergic response to a protein.

Examination of the local lymph node assay for use in contact sensitization risk assessment

The purpose of this study was to evaluate the utility of the murine local lymph node assay (LLNA) for contact sensitization risk assessment. Cellular proliferative activity in draining lymph nodes was determined for individual animals on Day 5 following four daily epicutaneous applications of the test chemical to the ears. Seventeen chemicals were tested, covering a range of materials including preservatives, drug actives, and perfume raw materials. The assay was found to be useful for identifying strong, moderate, and some weak sensitizers as defined by other testing methods (guinea pig, human). For evaluating the antigen specificity of the LLNA proliferative response, an in vitro blastogenesis assay was used. Dendritic cells (DC) isolated from lymph nodes of mice treated 24 hr earlier with trinitrochlorobenzene (TNCB) were capable of in vitro stimulation of lymphocytes from TNCB-sensitized mice, but not lymphocytes from mice sensitized to the preservative mixture of 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone (MCI/MI). Conversely, DC from mice treated 24 hr earlier with MCI/MI were capable of stimulating lymphocytes from MCI/MI-sensitized mice, but were unable to stimulate lymphocytes from TNCB-sensitized mice, demonstrating the specificity of the response. The results of these studies support the use of the murine LLNA for both investigative and predictive contact sensitization testing. The LLNA offers the advantages of requiring less time for completion, incorporating an objective endpoint, requiring approximately half the number of animals, and being less costly than most currently employed guinea pig test methods. In addition, we believe the murine LLNA is a useful test to incorporate into a scheme for contact sensitization risk assessment.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased number of dendritic cells in draining lymph nodes accompanies the generation of contact photosensitivity

Draining lymph node cells isolated from mice 48 h after topical exposure to tetrachlorosalicylanilide (TCSA) + UVA radiation (TCSA + UVA) demonstrated a two-fivefold increase in the number of dendritic cells (DC) compared with control mice treated with vehicle + UVA. The increase in number of DC was both time and dose dependent, with the peak DC accumulation occurring at 48 h post application and at a TCSA dose of 1.0%. Photospecificity was evident in that mice irradiated prior to treatment with TCSA (UVA/TCSA) demonstrated no significant increase in DC accumulation. The accumulation of DC was followed by a significant increase in total lymph node cellularity. An in situ 3H-thymidine incorporation assay showed a significant increase in proliferative activity of cells isolated from the draining lymph nodes of mice treated with TCSA + UVA as compared to naive, vehicle, or UVA/TCSA-treated mice. Dendritic cells isolated from mice treated 24 h earlier with TCSA + UVA, but not those from naive mice or mice treated with UVA/TCSA, were capable of TCSA-specific antigen presentation. Responder lymphocytes from untreated mice or mice photosensitized with musk ambrette showed a much lower response to DC isolated from TCSA + UVA-treated mice, demonstrating the specificity of the reaction. DC-depleted lymph node cells were unable to stimulate this blastogenesis response. These results suggest that application and photoactivation of TCSA induces cellular and functional changes in the lymph node DC indicative of their involvement in the induction phase of a contact photoallergic reaction.

Value of the cutaneous basophil hypersensitivity (CBH) response for distinguishing weak contact sensitization from irritation reactions in the guinea pig

Numerous studies of the histology of allergic contact dermatitis reactions to potent allergens in guinea pigs and humans have indicated that there is significant tissue infiltration with basophilic leukocytes. In this study we determined whether this histologic finding could be of value in distinguishing weak sensitization reactions from primary irritation, thereby aiding in the predictive identification of weak or moderate contact allergens. Guinea pigs were sensitized by the Buehler test method. Skin reactions were graded 24, 48, and 72 h post-challenge with duplicate patch sites biopsied at the 24- or 72-h grading timepoints. The biopsies were fixed, embedded in glycol methacrylate, thin sectioned, and Giemsa stained. The number of basophils per 400 leukocytes were counted along the upper dermis just below the dermal/epidermal junction. Challenge patch sites from animals sensitized to a relatively low dose of the strong contact allergen, oxazolone, were compared with patch sites from animals challenged only with a strong irritant, sodium lauryl sulfate (SLS). Compared to normal skin (7.5 +/- 1.0 basophils/400 leukocytes +/- SEM) only the oxazolone patch sites showed significant basophil infiltration (36.8 +/- 6.5), despite the fact that the skin reactions to the low oxazolone challenge dose were relatively weak. SLS patch sites showed no basophil infiltration above normal skin levels (4.8 +/- 0.9). Subsequent blinded studies compared weak/moderate presumptive sensitization reactions (as defined by accepted visual skin grading criteria) to various chemicals (citronellal, vanillin, cinnamic aldehyde, and ethylenediamine) to primary irritation reactions to the same chemicals. In each case, low-challenge-dose sensitization sites on previously treated (induced) animals showed mean basophil infiltration (range, 11.9-69.2 basophils/400 leukocytes) significantly greater than higher-dose irritant reactions (range, 1.6-13.3). The range for normal skin was 0.2-10.2 and the range for strong patch reactions to higher concentrations of oxazolone was 59.8-209.3. These data strongly indicate that light-microscopic quantitation of the CBH response can be used to distinguish relatively weak to moderate contact sensitization reactions from primary irritation reactions to the same chemicals.

A review of the Buehler guinea pig skin sensitization test and its use in a risk assessment process for human skin sensitization

The Buehler test is a valuable procedure for screening the sensitization potential of chemicals prior to human exposure. Our experience of over 20 years has shown it to be effective in detecting strong, moderate, and most weak sensitizers. The topical exposure inherent in the Buehler test allows it to be utilized to investigate dose responses, cross reactivity between structurally related chemicals, and the sensitization potential of contaminants in raw material mixtures. For safety assessment purposes, Buehler test results provide an initial indication of the sensitization potential of the material in question under relevant, but exaggerated, exposure conditions. These results can be compared to results on benchmark chemicals to assess sensitization risk for subsequent human exposure. Optimizing the sensitivity of the Buehler test requires adherence to the published methodology and proper interpretation of the challenge and rechallenge data obtained. Adjuvant-type test methods are generally considered to be more sensitive than topical methods. However, when done properly, topical test procedures such as the Buehler test or the open epicutaneous test can accurately detect most chemicals with any realistic potential for sensitizing humans by the topical route. Moreover, from a risk assessment perspective, these topical tests avoid the problems of overestimating the weak sensitization potential of many topically applied materials or underestimating the sensitization potential of very strong sensitizers; both are potential concerns with invasive adjuvant-type test methods. The Buehler test or other topical test methods are particularly valuable for comparative sensitization risk assessment since human sensitization data on benchmark materials are all derived from topical exposure. The risk assessment is developed by comparing the guinea pig data on the new material versus relevant benchmark chemicals or formulations and also by evaluating the existing human sensitization data on the benchmark material. These data are then utilized to predict human sensitization risk from topical exposure to the new material. Confirmation of human safety can be derived from human repeat insult patch testing (HRIPT) and other clinical tests such as the product use test and the diagnostic patch test. Utilized in this manner, the Buehler test is an integral component of an overall skin sensitization safety assessment program for a new chemical or product formulation.

Physical correlates of eardrum rupture

Eardrum (tympanic membrane) rupture in humans and animals in relation to various blast pressure-time patterns was reviewed. There were few systematic studies on eardrum rupture as a consequence of blast overpressure. Most reports did not describe the area of the eardrum destroyed. The peak overpressures required to produce a 50% incidence of eardrum rupture (P50) were summarized. Most of the animal data pertained to dogs. The highest P50 for dogs, 296 kPa, was associated with smooth-rising overpressure. For complex wave patterns occurring inside open shelters subjected to nuclear blasts, the P50 was 205 kPa. For fast-rising blasts in a shock tube it was 78 kPa, and 105 kPa for statically applied pressures. The duration of the overpressure was not a factor unless it was very short. The influence of the orientation of the head to the oncoming blast was demonstrated. An ear facing the blast may receive reflected overpressures several times that for one side-on to the blast. An ear on the downstream side of the head was exposed to about the same overpressure as the side-on ear. A P50 for humans of 100 kPa and a threshold of 35 kPa has been used widely in blast criteria. A recent study suggests a threshold (P1) of about 20 kPa, and gives the overpressures required to produce minor, moderate, and major eardrum ruptures. These data were presented in the form of curves showing the overpressures as a function of duration required to inflict a P1 and a P50 of eardrum rupture of the three levels of severity.

Validation and application of single breath cardiac output determinations in man

Cardiac outputs by single breath (Qsb) and Fick (Qf) procedures were compared in five healthy males during supine rest and exercise with Qf ranging from 6-19 L X min-1. The prolonged exhalation (SB) was not controlled. The Qsb calculations incorporated an equation of the CO2 dissociation curve and a "moving spline" sequential curve-fitting technique to calculate the instantaneous R from points on the original expirogram. The resulting linear regression equation for all 38 comparisons obtained (r = +0.76, p less than 0.001, mean difference +/- S.D. = 2.93 +/- 2.72 L X min-1) indicated a 24% underestimation of Qf. A substantial portion of the variability during exercise (n = 28) was due to a difference in alveolar ventilation between the time of the mixed expired (E) gas collection and the SB maneuver. When Qsb was corrected (Qsb) by a linear regression based on the difference between Re and Rsb during exercise and by adding 2.44 L X min-1 at rest (the mean difference), the relationship was greatly improved (Qsb = 0.14 + 0.99 Qf, r = +0.93, mean difference +/- S.D. = 0 +/- 1.47 L X min-1). A subsequent study during upright rest and exercise to 80% of VO2max in 6 subjects indicated a close linear relationship between Q'sb and VO2 for all 95 values obtained (r = +0.94), with slope and intercept close to published studies utilizing invasive cardiac output measurements. Considerations of measured blood gases in relation to estimated values suggested that underestimates of Qf arose, at least in part, from arterial desaturation during the SB maneuver. Detailed computational procedures are provided for implementing this improved Qsb procedure.

A technique for monitoring respiratory responses in guinea pigs

A piezoelectric crystal was used to detect respiration rates and pulmonary retractions of guinea pigs in response to intratracheal administration of histamine. Voltage output from the crystal was displayed on a recorder for visual processing and interfaced to a microcomputer for automatic data processing. Using intratracheal instillation of histamine, this system accurately reproduced the visual observations of respiratory responses in guinea pigs.

Quantitative description of whole blood CO2 dissociation curve and Haldane effect

A simple procedure is presented to describe accurately the whole blood CO2 dissociation curve on linear content (CCO2) and pressure (PCO2) coordinates with an exponential equation (CCO2 = K . PCO2b). A single coordinate and the hemoglobin concentration, Hb, are required. Whole blood CCO2 can be calculated from values for pH, PCO2, Hb and O2 saturation by empirically accurate equations. The mathematical description of the CO2 curve was employed to quantitate the in vivo Haldane factor (fH) from simultaneous arterial and mixed venous blood samples in 20 healthy exercising subjects. The mean +/- SE was 0.28 +/- 0.03 (vol. % delta CCO2/vol. % delta HbO2). In 20 patients with severe obstructive lung disease fH was 0.29 +/- 0.08 when calculated from arterial samples while breathing air and 100% O2. Values for fH were not related significantly to acid-base status or Hb as suggested by previous workers. By assuming these or other values for fH, the in vivo change in blood PCO2 resulting from a given change in oxygenation can be predicted.