Repeated inhalation exposure of rats to aerosols of 144CeO2. I. Lung, liver, and skeletal dosimetry.

To develop a better understanding of the influence of cumulative radiation dose and dose rate to the lungs on the biological responses to inhaled radionuclides, several studies are in progress at this institute in which laboratory animals have been exposed once or repeatedly to aerosols of insoluble particles containing 144Ce or 239Pu. In the study reported here, F344 rats were exposed repeatedly to aerosols of 144CeO2 beginning at 94 days of age to reestablish desired lung burdens of 1.9, 9.2, 46, or 230 kBq of 144Ce every 60 days for 1 year (seven exposures). Other 94-day-old rats were exposed once to achieve similar desired initial lung burdens of 144Ce. Older rats were exposed once to achieve desired initial lung burdens of 46 or 230 kBq when 500 days of age, the age of the repeatedly exposed rats when exposed for the last time. Control rats were either unexposed, sham-exposed once or repeatedly, or exposed once or repeatedly to stable CeO2. Approximately equal numbers of male and female rats were used. The cumulative beta-radiation doses to the lungs, liver, and skeleton of rats exposed repeatedly were similar to those of rats with similar total lung burdens of 144Ce from a single inhalation exposure. The average beta-radiation dose rate to the lungs of the rats exposed repeatedly was about one-fifth of that in rats with similar total lung burdens after a single exposure.     

Effects of the single or repeated inhalation exposure of Syrian hamsters to aerosols of 239PuO2

Male Syrian hamsters were scheduled to be exposed by inhalation approximately every 60 days for 1 year (7 exposures) to aerosols of 239PuO2 beginning at 84 days of age. Other hamsters were exposed once when 84 or 320 days of age. Plutonium-239 deposited in the lungs by the repeated inhalation exposures was cleared from the lungs at a rate similar to that following a single inhalation exposure. The incidence of radiation pneumonitis, bronchiolar epithelial hyperplasia, and alveolar squamous metaplasia were the only lesions that were related to radiation dose. Only two primary lung tumours were found among the hamsters exposed to 239PuO2. No primary lung tumours were found in the control hamsters. It was concluded that the incidence of lung tumours was not increased by the protraction of the alpha radiation dose to the lungs from repeated inhalation exposure.     

Pathogenetic process of lung tumors induced by inhalation exposures of rats to plutonium dioxide aerosols

Sequential examinations were done on the pulmonary cytokinetics and pulmonary lesions in rats after inhalation exposure to (239)PuO(2) aerosols to investigate the pathogenesis of lung tumors. Total cell yields of lavaged bronchoalveolar cells as well as the estimated numbers of pulmonary alveolar macrophages were significantly reduced from 1 to 3 months after exposure but recovered thereafter to the control levels. The proportions of multinucleated or micronucleated pulmonary alveolar macrophages increased significantly in lavaged cells from 1 month, and the increase was sustained up to 18 months after exposure. Both tumor necrosis factor and nitric oxide were shown to be differentially released from stimulated cultures of pulmonary alveolar macrophages during the period from 6 to 18 months after exposure. The labeling indices of alveolar and bronchiolar epithelial cells treated with 5-bromo-2'-deoxyuridine increased significantly in lungs from 3 months and were sustained up to 18 months after exposure. Histopathological examinations revealed that after the early inflammation, hyperplasia and metaplasia of the lining of the bronchioloalveolar epithelium were predominant from 3 to 6 months, while adenomatous or adenocarcinomatous lesions appeared and developed from 12 months after exposure. The appearance of primary lung tumors, almost all of which were adenomas and adenocarcinomas, was found in the dose range of 1 to 2 Gy from 12 months after exposures. These results indicate that the pathogenetic process initiated by early cellular damage and alterations associated with inflammation is followed by the proliferative and metaplastic lesions of pulmonary epithelium, leading to the appearance and development of pulmonary neoplasms from 1 year after the inhalation exposures in rats that received a minimum lung dose of more than 1 Gy.     

Effects of protraction of the alpha dose to the lungs of mice by repeated inhalation exposure to aerosols of 239PuO2

To determine the long-term biological effects of protracted alpha irradiation of the lung, 84-day-old C57BL/6J mice were repeatedly exposed by inhalation to aerosols of 239PuO2 every other month for up to six exposures in 10 months to reestablish lung burdens of 20, 90, or 460 Bq. Other mice were exposed only once when either 84 or 460 days of age to achieve desired initial lung burdens of 20, 90, 460, or 2300 Bq. Suitable control groups were maintained. Groups of mice with similar cumulative alpha doses to the lung had 3.4 to 4.4 times greater incidence of pulmonary tumors (adenomas and adenocarcinomas) when the dose to the lung was protracted by the repeated inhalation exposures compared to mice that received a single inhalation exposure. Excess pulmonary tumors per unit dose to the lung were also greater in groups of repeatedly exposed mice compared to those exposed only once. Repeatedly exposed mice also died earlier with pulmonary tumors than did those exposed once. It appears that protraction of an alpha dose to lungs increases the carcinogenic risk of inhaled 239PuO2 in mice.     

Time-course of effects of toluene on microsomal enzymes in rat liver, kidney and lung during and after inhalation exposure

Inhalation of toluene vapour of 2000 ppm increased the activities of aniline hydroxylase, aminopyrine N-demethylase, aryl hydrocarbon hydroxylase and NADPH-cytochrome c reductase and the concentrations of cytochromes P-450 and b5 in liver microsomes of adult male rats after an exposure period of 1 day or less. Repeated treatments, 8 h daily for 1-16 days, had only a slight further effect. In lung microsomes, the activities of monooxygenases and the concentration of cytochrome P-450 decreased after 6-24 h toluene exposure, but those of cytochrome b5 and NADPH-cytochrome c reductase did not change. In kidney microsomes the changes were mostly insignificant. After discontinuation of exposure the activities of enzymes and the concentrations of cytochromes returned to the control level in 1-4 days. The results obtained resemble the time-courses for the induction of monooxygenases by other inducers. The tissue differences suggest the unequal distribution of various cytochrome P-450 forms and their individual responsiveness to induction in liver, kidneys and lungs.     

Malonyl-CoA in skeletal muscle and liver of streptozotocin-diabetic rats.

Malonyl-CoA, the inhibitor of carnitine palmitoyl transferase I, has been examined in this study in the muscle and liver of diabetic rats. Male Sprague-Dawley rats were rendered diabetic with streptozotocin (6 mg/100 g body wt). The gastrocnemius/plantaris muscles and liver samples were frozen at liquid nitrogen temperature. Muscle malonyl-CoA was 1.8 +/- 0.2 pmol/mg in control rats and 1.5 +/- 0.2 pmol/mg in the diabetic rats. This difference was not statistically significant. Liver malonyl-CoA of control rats was 8.6 +/- 0.8 pmol/mg, in comparison to 4.3 +/- 0.6 pmol/mg in diabetic rats. In the liver, high concentrations of malonyl-CoA inhibit fatty acid oxidation and ketogenesis. Failure of malonyl-CoA to decline in muscle in the diabetic may be responsible in part for the diversion of fatty acids to the liver, thereby enhancing hepatic fatty acid oxidation and ketogenesis.     

次声暴露对大鼠脾、肝脏某些酶活性的影响

目的:观察8 Hz,130 dB次声暴露不同时间对大鼠脾、肝脏某些酶活性的影响.方法:35只SD大鼠随机分为5组,即对照组,1周,2周,3周,4周组.每天次声暴露1次,每次2 h.实验后,观察大鼠脾、肝脏组织中MAO,GSH-px,SOD活性和MDA含量的变化.结果:大鼠脾脏MAO活性1周,2周时显著增高(P＜0.01),3周下降,4周时又显著增加(P＜0.05).肝脏组织MAO活性变化不明显(P＞0.05).脾脏组织中GSH-px活性在4周时明显增高(P＜0.05),肝脏组织中GSH-px活性在1周时就有显著性增高(P＜0.05).脾脏SOD活性在1周至4周均有显著性增高(P＜0.05).肝脏组织在实验期变化不明显(P＞0.05).脾脏组织中MDA含量在3周至4周时有显著性增高(P＜0.05).肝脏组织在1至2周时有非常显著的增高(P＜0.01),在3周时下降,到4周时又显著高于对照组(P＜0.05).结论:8Hz,130 dB次声暴露,大鼠脾、肝脏组织活性氧自由基、脂质过氧化物增高,抗氧化能力降低,造成对组织的损伤.     

Effects of nitrogen dioxide exposure on prostacyclin synthesis in lung and thromboxane A2 synthesis in platelets in rats

Effects of nitrogen dioxide (NO2) exposure on prostacyclin (PGI2) synthesis in the rat lung and thromboxane A2 (TXA2) synthesis in the platelets were studied. Male Wistar rats were exposed to 10 ppm NO2 for 1, 3, 5, 7 and 14 days. PGI2 synthesizing activity of homogenized lung decreased. The damage of PGI2 synthesizing activity reaches its maximum at 3 days. At 14 days, PGI2 synthesizing activity returned to the normal level. The activity of PGI2 synthetase decreased significantly. The formation of lipid peroxides due to NO2 exposure may cause the depression of PGI2 synthesizing activity of lung. On the other hand, platelet TXA2 synthesizing activity increased. This increased TXA2 synthesizing activity lasted at least till 3 days. Then, it returned to the normal level. The counts of platelet were decreased significantly by 1, 3, 5 and 7 days NO2 exposure. Then the decreased counts of platelet returned to the normal level at 14 days NO2 exposure. These results indicate that the depression of PGI2 synthesizing activity of lung by NO2 exposure cause an increase in TXA2 synthesizing activity of platelets. It may contribute to induce platelet aggregation and to the observed decrease in the number of platelets during NO2 exposure.     

Effects of 2G exposure on lean and genetically obese Zucker rats

Changes in the ambient force environment alter the regulation of adiposity, food intake and energy expenditure (i.e., energy balance). Lean (Fa/Fa) and obese (fa/fa) male Zucker rats were exposed to 2G (twice Earth's normal gravity) for eight weeks via centrifugation to test the hypothesis that the Fa/Fa rats recover to a greater degree from the effects of an increased ambient force environment on body mass and food intake, than do the fa/fa rats which have a dysfunctional leptin regulatory system. The rats (lean and obese exposed to either 1G or 2G) were individually housed in standard vivarium cages with food and water provided ad libitum. The acute response to 2G included a transient hypophagia accompanied by decreased body mass, followed by recovery of feeding to new steady-states. In the lean rats, body mass-independent food intake had returned to 1G control levels six weeks after the onset of centrifugation, and body mass increased towards that of the 1G rats. In contrast, food intake and body mass of the 2G obese rats plateaued at a level lower than that of the 1G controls. Although percent carcass fat was reduced more in the 2G leans vs. 2G obese rats, the latter lost significantly more grams of fat than did the leans. Our data suggest that with respect to food intake and body mass, the lean rats recover from the initial effects of 2G exposure to a greater degree than do the fatty rats, a difference that likely reflects the functionality of the leptin regulatory system in the leans.     

Effects of chronic exposure to simulated microgravity on skeletal muscle cell proliferation and differentiation

Cell culture models that mimic long-term exposure to microgravity provide important insights into the cellular biological adaptations of human skeletal muscle to long-term residence in space. We developed insert scaffolding for the NASA-designed rotating cell culture system (RCCS) in order to study the effects of time-averaged microgravity on the proliferation and differentiation of anchorage-dependent skeletal muscle myocytes. We hypothesized that prolonged microgravity exposure would result in the retardation of myocyte differentiation. Microgravity exposure in the RCCS resulted in increased cellular proliferation. Despite shifting to media conditions promoting cellular differentiation, 5 d later, there was an increase in cell number of approximately 62%, increases in total cellular protein (52%), and cellular proliferating cell nuclear antigen (PCNA) content (2.7 times control), and only a modest (insignificant) decrease (10%) in sarcomeric myosin protein expression. We grew cells in an inverted orientation on membrane inserts. Changes in cell number and PCNA content were the converse to those observed for cells in the RCCS. We also grew cells on inserts at unit gravity with constant mixing. Mixing accounted for part, but not all, of the effects of microgravity exposure on skeletal muscle cell cultures (53% of the RCCS effect on PCNA at 4-6 d). In summary, the mechanical effects of simulated microgravity exposure in the RCCS resulted in the maintenance of cellular proliferation, manifested as increases in cell number and expression of PCNA relative to control conditions, with only a modest reciprocal inhibition of cellular differentiation. Therefore, this model provides conditions wherein cellular differentiation and proliferation appear to be uncoupled.     

Sensitizing effects of chronic exposure and acute inhalation of ovalbumin aerosol on pulmonary C fibers in rats.

The effect of ovalbumin (Ova) sensitization on pulmonary C-fiber sensitivity was investigated. Brown-Norway rats were sensitized by intraperitoneal injection of Ova followed by aerosolized Ova three times per week for 3 wk. Control rats received the vehicle. At the end of the third week, single-unit fiber activities (FA) of pulmonary C fibers were recorded in anesthetized, artificially ventilated rats. Our results showed the following: 1) Ova sensitization induced airway inflammation (infiltration of eosinophils and neutrophils) and airway hyperresponsiveness in rats; 2) baseline FA in sensitized rats was significantly higher than that in control ones; 3) similarly, the pulmonary C-fiber response to right atrial injection of capsaicin was markedly higher in sensitized rats, which were significantly amplified after the acute Ova inhalation challenge; and 4) similar patterns, but smaller magnitudes of the differences in C-fiber responses to adenosine and lung inflation, were also found between sensitized and control rats. In conclusion, Ova sensitization elevated the baseline FA and excitability of pulmonary C fibers, and the hypersensitivity was further potentiated after the acute Ova inhalation challenge in sensitized rats. Chronic allergic inflammatory reactions in the airway probably contributed to the sensitizing effect on these lung afferents.     

Effects of cold exposure on cyclic AMP concentration in plasma,liver, and brown and white adipose tissues in cold-acclimated rats

Effects of acute cold exposure on plasma energy substrates and tissue 3,5-adenosine monophosphate (cAMP) were analyzed in intact rats, to define an involvement of the nucleotide in nonshivering thermogenesis (NST) and resultant cold acclimation. After an acute cold exposure to –5°C, the plasma glucose level increased gradually in warm-kept control rats (C) while it decreased significantly in cold-acclimated rats (CA). However, it was increased considerably by an extreme cold exposure to –15°C in both C and CA. By contrast, plasma levels of free fatty acids (FFA) increased immediately after cold exposure and the release lasted during the period of exposure especially in C. The cold exposure also increased plasma cAMP concentration but no concomitant increase was found in the liver. In both brown (IBAT) and white (WAT) adipose tissues the nucleotide concentration showed a stepwise decrease. The observed correlation between lipolysis and plasma cAMP response after cold exposure suggests an involvement of the adenylate cyclase-cAMP system in NST via lipid metabolism, at least, in the early stages of cold acclimation.Abbreviations cAMP cyclic 3,5-adenosine monophosphate - NST nonshivering thermogenesis - FFA free fatty acids - IBAT brown adipose tissue - WAT white adipose tissue     

Protein phosphatase-1 and -2A, kinase FA, and casein kinase II in skeletal muscle of streptozotocin diabetic rats.

Protein phosphatase-1 (PP-1) and -2A (PP-2A), two regulatory subunits of PP-1, the glycogen-binding subunit G and inhibitor-2 (I-2), kinase FA, and casein kinase II (CK-II) were investigated in skeletal muscle of diabetic rats 2 days after streptozotocin injection. FA and CK-II activate PP-1 in vitro and might be involved in the activation of PP-1 by insulin. Following muscle fractionation we found that (1) diabetes decreased both basal and trypsin-stimulated PP-1 activities; the decrease was more significant in the glycogen-bound and microsomal fractions than in the cytosol (cytosolic PP-1 decreased as specific activity but not as activity/g of muscle); also PP-2A was lower in diabetic cytosols; (2) less G was immunoprecipitated from diabetic glycogen-bound fractions compared to controls, while I-2 was not significantly changed; (3) diabetes decreased also FA (assayed as PP-1 activator) and CK-II (assayed using a synthetic peptide as substrate); (4) diabetes did not have any effect on phosphorylase (a + b) activity in the glycogen-bound fraction. Altogether the data show that acute diabetes decreased PP-1, one of its regulatory subunits and two potentially physiological regulators of PP-1, in addition to PP-2A. This may indicate that insulin is responsible for the long-term regulation of the same enzymes that are also under acute insulin control.     

Acrylonitrile inhalation in rats: II. Excretion of thioethers and thiocyanate in urine

In male Wistar rats, the inhalation exposure to acrylonitrile (AN), 271 mg X m-3, 8 hours a day, 5 days a week, did not affect protein sulfhydryl concentration in liver and blood and decreased glutathione concentration in the liver, but not in the brain at the end of the fifth exposure. The urinary excretion of the main AN metabolites, thioethers (AN-mercapturic acids) and thiocyanate was proportional to the inhaled AN concentration (57, 125, 271 mg X m-3, respectively) in a single exposure for 12 hours, and their mutual ratio was greatly different from that after injection of AN. The results revealed that the urinary excretion of thioethers is a very sensitive and dose-related indicator of exposure to AN and extrapolation of the results indicates that the exposure to AN concentration below 10 mg X m-3 could thus be demonstrated.