Large-grain scintillator screens for proton radiography.

Protons from the Los Alamos Neutron Science Center have been used for pulsed radiography in dynamic experiments for the past 25 years. Pulses of protons are imaged on a scintillator, and the light from these images is captured by fast gated cameras. The need for fast, bright scintillators has led to some compromises in image quality due to tiling the scintillators and backgrounds with totally internally reflected light. We show how large-grain scintillator screens, made using a thin plastic binder, solve these problems.

Role of the intestinal microbiota in the activation of the promutagen 2,6-dinitrotoluene to mutagenic urine metabolites and comparison of GI enzyme activities in germ-free and conventionalized male Fischer 344 rats.

After male germ-free and conventionalized Fischer 344 rats were administered per os (p.o.) 75 mg/kg 2,6-DNT, intestinal nitroreductase, beta-glucuronidase, and azo reductase activities were lower in the cecum and large intestine of germ-free animals. However, there was no significant difference in the small intestinal nitroreductase and azo reductase compared to the conventionalized counterparts. This indicated a potential mucosal source for the enzymes. Urines from germ-free rats (1144 +/- 64 revertants/ml) were less mutagenic than those from conventionalized animals (1467 +/- 171 revertants/ml) in Salmonella typhimurium strain TA98 without S9. In the presence of S9, urine from conventionalized animals (894 +/- 56 revertants/ml) was more mutagenic than that from germ-free rats (686 +/- 60 revertants/ml). The presence of the intestinal flora plays an important role in the activation of 2,6-DNT but other metabolic pathways, such as the small intestinal mucosal and/or hepatic enzymes, are present that can generate excreted genotoxicants.

Modulation of 2,6-dinitrotoluene genotoxicity by alachlor treatment of Fischer 344 rats.

Due to its widespread use as a preemergent herbicide, alachlor has been detected as a groundwater contaminant. The procarcinogen, 2,6-dinitrotoluene (DNT), a by-product of the munitions industry and a precursor to polyurethane production, is found in the manufacturing waste stream. This study explores the effect of alachlor treatment on the bioactivation of DNT by examining urine mutagenicity, intestinal enzymes, and hepatic DNA adducts to detect changes in metabolism. Five-week-old male rats were treated daily by gavage with 50 mg/kg of alachlor for up to 5 weeks while control animals received an equal volume of peanut oil. At 1, 3, and 5 weeks following the initial alachlor dose, animals were administered p.o. 75 mg/kg DNT or DMSO. Urine was collected for 24 hr in metabolism cages. Following incubation with sulfatase and beta-glucuronidase, urines were individually concentrated by C-18 solid phase extraction, dried under N2, and prepared for bioassay in Salmonella typhimurium strain TA98 with and without metabolic activation. Urine from peanut oil- and alachlor-treated rots was not mutagenic. Even though calf thymus DNA-alachlor adducts formed in vitro, no hepatic DNA adducts were detected in vivo in these two treatment groups. Interestingly, a significant increase in excretion of mutagenic urine from DNT-treated rats was observed following 3 weeks of alachlor treatment in the absence of S9 (690 +/- 130 vs. 339 +/- 28 revertants/ml) which corresponded to increased DNT-related hepatic DNA adduct formation (5.90 +/- 0.88 adducts/10(8) nucleotides vs. 10.56 x +/- 0.59 adducts/10(8) nucleotides [relative adduct level (RAL)]). Elevation in the production of mutagenic urine from control and treated animals was linked to increases in intestinal nitroreductase and beta-glucuronidase activities; however, the only significant alachlor-related effects were an increase in small intestinal 1-week beta-glucuronidase and 5-week dehydrochlorinase activities. The increased urine mutagenicity and hepatic DNA adduct formation indicates that alachlor has a transient effect on DNT bioactivation that apparently is unrelated to intestinal bioactivation.

Atrazine treatment potentiates excretion of mutagenic urine in 2,6-dinitrotoluene-treated Fischer 344 rats.

Atrazine (ATZ), an s-triazine herbicide, is a widespread environmental contaminant. The hepatocarcinogenic component of technical grade dinitrotoluene, 2,6-dinitrotoluene (2,6-DNT, 19.5%), is a byproduct of trinitrotoluene synthesis and is found at production sites. This study explores the effect of ATZ treatment on the bioactivation of the promutagen, 2,6-DNT. Male Fischer 344 rats (5 weeks old) were administered 50 mg/kg of ATZ by gavage for 5 weeks. At 1, 3, and 5 weeks, both DMSO-control and ATZ-pretreated rats were treated p.o. with 75 mg/kg of 2,6-DNT and were housed in metabolism cages for urine collection. Sulfatase- and beta-glucuronidase-treated, concentrated urine was bioassayed for urinary mutagens in a microsuspension modification of the Salmonella assay with and without metabolic activation. No significant change in mutagen excretion was observed in ATZ-treated rats; however, an elevation in direct-acting urine mutagens from rats receiving ATZ and 2,6-DNT at weeks 1 (359 +/- 68 vs. 621 +/- 96 revertants/ml) and 5 (278 +/- 46 vs. 667 +/- 109 revertants/ml) of treatment was observed. The increase in production of urinary mutagens was accompanied by an elevation in small intestinal nitroreductase activity. Increases in large intestinal nitroreductase and beta-glucuronidase were observed after 5 weeks. There was no apparent effect of ATZ following 5 weeks of treatment on the production of 2,6-DNT-derived hepatic DNA adducts. ATZ treatment modifies intestinal enzymes responsible for promutagen bioactivation, and potentiates the excretion of mutagenic urine in 2,6-DNT-treated animals.

Potentiation of 2,6-dinitrotoluene genotoxicity in Fischer-344 rats by pretreatment with Aroclor 1254.

Pretreatment of Fischer 344 rats for 5 weeks with Aroclor 1254, a commercial mixture of polychlorinated biphenyls, potentiated the genotoxicity of 2,6-dinitrotoluene (DNT), a component of an industrial chemical used in the production of polyurethane foams. This interaction resulted from Aroclor 1254-mediated bioactivation of DNT to markedly greater levels of the genotoxic metabolites, that were excreted in urine and formed DNA adducts in the liver. A significant increase in the excretion of mutagenic urinary DNT metabolites was observed after the first week of Aroclor 1254 treatment, peaked at week 2 and then declined by nearly 25% at week 4. Nevertheless, by week 5, there was almost a 4-fold increase in the formation of hepatic DNA adducts. Significantly elevated hepatic metabolism and increased beta-glucuronidase in the small intestine and cecum, at 4 weeks, may account for the increased adducts and decreased urinary mutagens. Altered nitroreductase activity, reduced pH, and changes in the microfloral population may also play a role in the effect of Aroclor 1254 on the bioactivation of DNT. Such chemical interactions could be important to predictive risk assessment because the overall cancer risk of the mixture would exceed that determined by the current guidelines for chemical mixtures.

Evaluating the relationship of metabolic activation system concentrations and chemical dose concentrations for the Salmonella spiral and plate assays.

A factorial experimental design was used within this study to evaluate the influence of multiple metabolic activation system concentrations on the dose-response exhibited by promutagens (indirect-acting mutagens) in the Salmonella spiral and plate assays. The mutagenic activity of the three compounds used spanned three orders of magnitude. The mutagenic activity of the compounds ranged from 10 to 100 revertants/micrograms for acetylaminofluorene (2AAF) to more than 1000 revertants/micrograms for 2-aminoanthracene (2AA). Benzo [a] pyrene (BaP) activity was within an intermediate range (100-1000 revertants/micrograms). During a single experiment, a mutagen was tested in TA100 at 13 doses plus a negative control dose. Each dose was tested at 10 S9 concentrations. The S9 concentrations ranged from 0.1 mg protein/plate to 4 mg protein/plate in the standard plate assay and from 0.25 to 4.90 mg-equivalents in the spiral assay. The spiral Salmonella assay, an automated version of the standard assay, generates dose-response data from a concentration gradient on a single agar plate, thereby providing a straightforward approach to this type of study. This study demonstrates not only that even small differences in S9 concentrations can affect the measurement of mutagenic potency but that S9/compound interactions cannot be generalized through the use of interaction studies. This study also shows that spiral assay data and plate assay data for promutagens cannot be compared directly unless the S9 concentrations for all chemical doses are also comparable.

Effect of absence of developing grain on carbohydrate content and senescence of maize leaves.

In maize (Zea mays L.) grown under normal conditions in Rhodesia, prevention of pollination or removal of the ears after flowering caused premature senescence of the leaves above the ear, preceded by the appearance of a purplish red color. In plants from which the ears had been removed the concentration of sugars and starch increased markedly in both upper and lower leaves, the increase being greater in the upper leaves.

Effects of treatments potentially influencing the supply of assimilate on its partitioning in sugarcane.

Two pot experiments and one field experiment were conducted on sugarcane to assess the effects of treatments expected to change total carbon assimilation on the partitioning of assimilate. In the first experiment pots of cultivars CP and N14 were arranged to simulate normal field spacing. At 5 months, plants were partially defoliated or left intact. In the subsequent four months, defoliation resulted in a small (not significant) decrease in total dry mass increment; it increased the proportional partitioning of assimilates to leaves in N14, whilst in CP it increased the proportional partitioning to stems. In both cultivars defoliation increased proportional allocation to non-structural dry matter, and thus sucrose, in the stem. In the second experiment pots of cv. CP were grown at normal spacing for 4 months, then left untreated, shaded, or placed further apart. During the subsequent four months shading decreased total dry matter increment, but increased proportional partitioning to the stems, and within stems to non-structural dry matter, and so sucrose. Widened spacing increased total assimilation, but decreased proportional allocation to stems; partitioning within the stems was not affected. In the field experiment plants of both cultivars were partially defoliated at 6 months, or left intact. Defoliation resulted in only a very small decrease in stem dry mass increment during the subsequent four months (leaves were not measured). Within the stem partial defoliation caused proportionally increased partitioning to non-structural dry matter, hence to sucrose. The results suggest that sucrose storage receives priority in the allocation of assimilate, rather than representing the accumulation of assimilate not required for vegetative growth.

Possible errors in assay for beta-glycosidase activity.

Cecal homogenates were assayed for the enzymes beta-glucosidase, beta-glucuronidase, and beta-galactosidase. Anaerobic incubation with the addition of excess 3,4-dichloronitrobenzene, a substrate for nitroreductase, significantly increased the detection of the beta-glycosidase enzymes' activities.

Microbial succession and intestinal enzyme activities in the developing rat.

The succession of gut bacteria and selected intestinal enzyme activities in developing 7-35-d-old rats was studied. Aerobes and anaerobes were identified as members of four broad major bacterial groups, i.e. Gram-positive rods, Gram-positive cocci, Gram-negative rods and obligate anaerobes. The enzyme activities of nitro and azo reductases, beta-glucuronidase, dechlorinase and dehydrochlorinase were determined by anaerobic incubation of intestinal homogenates with 3,4-dichloronitrobenzene, methyl orange, p-nitrophenyl-beta-D-glucuronide, and p,p'-DDT respectively. Nitroreductase and azo reductase activities increased significantly with the appearance of anaerobes in the large intestine. No increase in either nitroreductase or azo reductase activities in the small intestine was found. The early and high level of beta-glucuronidase activity in the small and large intestines coincided with high numbers of coliforms recovered in 7 and 14 d animals. Dehydrochlorinase activity appeared early but was undetectable at both 21 and 28 d. Its activity increased at 35 d. Dechlorinase activity was variable in development. The rapid changes in the microbial flora and intestinal enzyme activities may influence the susceptibility of pre-pubescent rats to a variety of toxicants. Therefore, age-dependent toxicity may be important in the risk assessment of some environmental chemicals.

Continuous monitoring of mixed venous oxygen saturation in cardiac surgery.

Serial measurement of mixed venous oxygen saturation is useful in the care of critically ill patients. It is an index of cardiac output and overall tissue perfusion. Previously, lack of refinement of the technology for continuous monitoring of mixed venous oxygen saturation deterred its clinical application. The authors evaluated the Oximetrix ShawTM catheter oximeter system between May 1980 and April 1981 in 84 high-risk and moderately high-risk patients. Fifty-four had undergone only myocardial revascularization while 30 had undergone valvular or combined procedures. In 20 patients with compromised left ventricular function (mean ejection fraction of less than 40%) continuous mixed venous oxygen saturation was compared to hemodynamic parameters in an intraoperative and early postoperative study. The results indicated that satisfactory mixed venous oxygen saturation (more than 65%) correlated with normal hemodynamic measurements including cardiac output and cardiac index. In general, a fall in mixed venous oxygen saturation of more than 10% was noted before the mean blood pressure, heart rate or pulmonary capillary wedge pressure changed. Cardiac output, cardiac index, systemic vascular resistance and left ventricular stroke work index were found to change in association with a change in mixed venous oxygen saturation. A fall (mixed venous oxygen saturation less than 65%) can be related to: (a) abnormal hemodynamic status--reduced cardiac output, hypotension, elevated systemic vascular resistance and arrhythmias, (b) abnormal oxygen demand--shivering, suctioning, positioning and pyrexia and (c) abnormal oxygen supply--anemia, airway obstruction and altered diffusion of oxygen at the alveolar capillary membrane. The Oximetrix system proved reliable. Mixed venous oxygen saturation is a nonspecific indicator of hemodynamic status. Continuous monitoring of the mixed venous oxygen saturation facilitates optimal patient management by immediately alerting intensive care personnel to the development of inadequate tissue perfusion.

2,4,5-trichlorophenoxyacetic acid influence on 2,6-dinitrotoluene-induced urine genotoxicity in Fischer 344 rats: effect on gastrointestinal microflora and enzyme activity.

2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) and 2,6-dinitrotoluene (2,6-DNT) are hazardous chemicals that have potential harmful effects. 2,6-DNT is recognized as a hepatotoxicant while 2,4,5-T, a component of Agent Orange, is also suspect. 2,6-DNT requires both oxidative and reductive metabolism to elicit genotoxic effects. To determine what effect 2,4,5-T had on 2,6-DNT metabolism, intestinal enzymes, microbial populations, and urine mutagenicity were examined during 2,4,5-T treatment. Weanling Fischer 344 male rats were treated daily with 54.4 mg/kg 2,4,5-T by gavage for 4 weeks. One, two, and four weeks after the initial 2,4,5-T dose, rats were administered (po) 2,6-DNT (75 mg/kg) and urine was collected for 24 hr in metabolism cages. Azo reductase, nitroreductase, beta-glucuronidase, dechlorinase, and dehydrochlorinase activities were examined concurrently. Treatment of rats for 1 week reduced the transformation of 2,6-DNT to mutagenic urinary metabolites. This was accompanied by a decrease in the fecal anaerobic microorganisms. The elimination of Lactobacillus fermentum from the small intestine and cecum of treated animals accompanied a significant increase in oxygen-tolerant lactobacilli and other unidentified aerobic microorganisms. However, there were no significant alterations in the intestinal enzyme activities examined. By 2 weeks of 2,4,5-T treatment, microbiota and urine genotoxicity returned to the levels observed in control animals. This trend continued for the duration of the experiment. After 2 weeks, while cecal nitroreductase and azo reductase activities increased, small intestinal beta-glucuronidase activity decreased. By 4 weeks, treated and untreated animal intestinal enzyme activities were indistinguishable.(ABSTRACT TRUNCATED AT 250 WORDS)

Potentiation of 2,6-dinitrotoluene genotoxicity in Fischer 344 rats by pretreatment with coal tar creosote.

Pretreatment of male Fischer 344 rats for 5 wk with coal tar creosote, a coal distillation product that is widely used as a wood preservative, potentiated the excretion of urinary mutagens in 2,6-dinitrotoluene (DNT) treated rats. Creosote increased the bioactivation of DNT to significantly greater levels of urinary genotoxic metabolites and/or formed DNA adducts in the liver. A significant increase in the excretion of mutagenic DNT metabolites was observed after the first week of creosote treatment, peaked at wk 3, and then decreased by 33% after 5 wk of treatment. Nevertheless, there was a significant increase (66%) in the formation of DNT-derived DNA adducts in the livers of rats treated with DNT plus creosote at wk 5. Increased cecal beta-glucuronidase activity and reduced small intestinal nitroreductase activity may play roles in the bioactivation of DNT. The excretion of mutagenic DNT metabolites supplies useful information about the bioactivation of DNT; it does not provide a useful index of DNT-derived hepatic DNA adduct formation. Such interactions could be important to predictive risk assessment because the overall cancer risk of such chemical mixtures may exceed the sum of the component risks.