Autoradiographic demonstration of the distribution of diacylglycerol in the gastric muscularis muscle of Bufo marinus: is diacylglycerol one of the second messengers in the muscularis muscle?

The distribution of 1,2-diacylglycerol (DAG) in the muscularis muscle of Bufo marinus has been determined using autoradiographic techniques. Strips of the muscle from the body of the stomach were fixed in 4% paraformaldehyde/2.5% glutaraldehyde, postfixed, washed and longitudinal sections (15 microns) were cut on a cryotome and placed on gelatinized slides. The sections were then incubated in the presence and absence of agonist, acetylcholine (ACh) 10(-5) M or carbachol (CCh) 10(-5) M plus Li+ (10 mM) in the medium which causes a marked potentiation of agonist-stimulated formation of cytidine diphosphate-DAG (CDP-DAG). The sections were processed through an autoradiographic technique using [3H]-cytidine, which binds to 1,2-diacylglycerol within the tissue to form CDP-DAG. Analysis of the developed tissue slides indicated that the dose of ACh (10(-5) M) which had been predetermined to elicit automaticity of the preparation in vitro increased the density of CDP-DAG grains. When the muscle strips were pretreated with ACh (10(-5) M) and CCh (10(-5) M) in the presence of LiCl (10 mM), the density of the CDP-DAG grains were further enhanced. CDP-DAG grains were localized throughout the muscle fibers. The increase in the density of the grains which was induced by the conditions eliciting automaticity suggest that DAG is one of the second messengers in the manifestation of automaticity of the muscularis muscle of Bufo marinus.

Accumulation of mixed mineral dusts in the lungs of rats during chronic inhalation exposure.

The effects of mixed dust exposure on pulmonary clearance during chronic exposure has been investigated using rats exposed to combinations of toxic and relatively nontoxic dusts: quartz (at respirable dust concentrations of 1 and 10 mg/m3) plus titanium dioxide (at 30 and 20 mg/m3, respectively), and amosite asbestos (2.5 mg/m3) plus titanium dioxide (15 mg/m3). The rats were exposed for 5 days per week, and for up to 16 weeks (for quartz) or up to 32 weeks (for asbestos). The lung burdens were compared with previously published results for exposure to single dusts under the same exposure regimens. The main feature of all these comparisons was the absence of significant differences between the lung burdens (at 3, 10, and 38 days postexposure) for single-dust and mixed-dust exposures. There was, however, some reduction in the postexposure clearance (as shown by the lung burdens at 94, 150, and 260 days postexposure) of titanium dioxide which appeared to be due to the presence of quartz in the lung. For the quartz plus titanium dioxide experiments, the lymph nodes were dissected and analyzed separately. These results showed that transfer to lymph nodes accounted for most of the postexposure clearance for titanium dioxide, and almost all for the quartz.

Effects of electrostatic charge on the pathogenicity of chrysotile asbestos.

Two groups of 48 rats of the AF/HAN strain were exposed for one year to respirable dust clouds of UICC chrysotile asbestos at a dose level of 10 mg/m3. One group was treated with dust carrying the normal electrostatic charge produced during dust generation, whereas the other was exposed to dust discharged by exposure to ionising radiation from a thallium-204 source. After dusting most animals were retained for their full life span. At the end of the dusting period those animals treated with normally charged dust had significantly more chrysotile retained in their lungs than animals exposed to discharged dust. Subsequently, animals treated with normally charged dust developed more pulmonary fibrosis and more pulmonary tumours. These findings suggest that the charge carried by airborne fibres should be taken into account when considering the health risks from exposure to chrysotile. Highly charged fibres are more likely to be deposited in lung tissue and thus constitute a greater hazard.

Dust exposure, dust recovered from the lung, and associated pathology in a group of British coalminers.

The relation between dust exposure, retained lung dust, and pneumoconiosis have been examined in 430 dead coalminers who had participated in a large scale epidemiological survey of respiratory health. The men were divided into three groups depending on the presence of particular lesions in their lungs. Lungs containing no fibrotic lesions in excess of 1 mm were included in the "M" group, those with fibrotic lesions of between 1 mm and 9 mm in diameter were included in the "F" group, and those with any lesion 10 mm or more were categorised as having progressive massive fibrosis (PMF). The men were further divided into four groups according to the rank of coal mined at the colliery of employment. The mean weight of lung dust increased over the pathological range (M----F----PMF) regardless of the rank of coal mined. The men with PMF had not received unusually high exposures to dust in life but were found to have accumulated more dust in their lungs per unit of dust exposure than men without PMF, providing further evidence for differences in the patterns of deposition or clearance, or both, of dust in these men compared with those who do not develop PMF. For men who had mined the higher rank coals there was no difference in the composition of the lung dust between the pathological groups. Lungs from men mining low rank coal, however, showed a striking increase in the proportion of ash over the pathological groups (M, F, and PMF). In men who had mined low rank coal the proportion of ash in the airborne dust to which they had been exposed and in the dust retained in their lungs was, as expected, greater than in men who had worked with higher rank coals. For the same men, and particularly associated with the presence of some dust related fibrosis, the proportion of ash in retained dust was higher than that in the dust to which the men were exposed suggesting the occurrence of selective deposition or retention of the mineral components of dust in this group.

Comparison of radiographic appearances with associated pathology and lung dust content in a group of coalworkers.

The pathology and dust content of lungs from 261 coalminers in relation to the appearances of their chest radiographs taken within four years of death were examined. Radiological opacities of coalworkers' pneumoconiosis were more profuse the more dust was retained in lungs. Among the men who had mined low rank coal--that is, with a relatively high proportion of ash--the increase in profusion was most closely related to the ash component of the dust, whereas in men who had mined high rank coal both coal and ash increased in the lungs in relation to radiological profusion. The fine p type of opacity was found to be associated with more dust and a higher proportion of coal and less ash than the nodular r opacity, and was also more likely to be associated with emphysema. The pathological basis of the different types of opacity found on the radiographs of coalminers related to the number, size, and nodularity of the dust lesions. Larger fibrotic lesions were likely to appear as r opacities, whereas fine reticular dust deposition was most likely to present as p opacities, q opacities showing a mixture of appearances. The study has shown that the composition of dust retained in the lung, as well as its amount, makes an important contribution to the radiographic appearances of pneumoconiosis. In particular, the r type of lesion on the radiograph of a low rank coalminer indicates the possibility of a silicotic like lesion.

Emphysema and dust exposure in a group of coal workers.

The lungs of 450 coal miners who had been studied previously in a long-term epidemiologic project at 24 British mines have been examined post-mortem for signs of dust-related fibrosis and emphysema. Reliable estimates of cumulative (working-life) exposures to respirable mine dust were available for 342 of the men. The relative frequency of emphysema increased with age at death, and both panacinar and centriacinar emphysema occurred more frequently in smokers than in nonsmokers. The proportion of subjects with any emphysema was 47% in 92 men with no palpable dust lesions, 65% in 183 with small, simple pneumoconiotic lesions, and 83% in 175 miners with massive fibrosis (PMF). The chance of finding centriacinar emphysema in those with PMF increased significantly with increasing exposure to coal dust in life (p less than 0.025). A similar but less convincing relationship was found in those with simple pneumoconiosis (p less than 0.11), but in both groups, increasing amounts of ash with a given exposure to coal reduced the probability of finding centriacinar emphysema. The occurrence of centriacinar emphysema was associated also with increasing amounts of dust retained in the lungs. A preliminary exploration of this association did not support the hypothesis that emphysematous lungs clear dust less efficiently. We conclude that the association observed between exposure to respirable coal dust and emphysema in coal miners indicates a causal relationship. However, because it can be demonstrated only for men whose lungs show some dust-related fibrosis, it is suggested that the extent and nature of such fibrosis may be a crucial factor in determining the presence of centriacinar emphysema.

Variations in the histological patterns of the lesions of coal workers' pneumoconiosis in Britain and their relationship to lung dust content.

The lungs of 490 British coal miners were examined for comparisons of the lesions of coal workers' pneumoconiosis with lung dust content and dust exposure. Variations were found in histological appearances that formed a range, the extremes of which indicated two separate patterns of disease. In men from high rank collieries, whose lung dust had a high carbon content and little ash, most of the nodules of simple pneumoconiosis were evenly pigmented with dust, and where progressive massive fibrosis (lesions greater than 1 cm in diameter) had developed, this appeared to be by the enlargement of a single lesion. In men from low rank collieries where the ash content of lung dust was high, the centers of the nodules were often free of dust particles and in extreme cases these lesions were very similar to silicotic nodules. If PMF developed in these cases, it often appeared to be by the fusion of closely spaced groups of smaller nodules. While there appeared to be little difference between the lung dust composition of men from high rank collieries and the dust to which they had been exposed, in men from low rank collieries the proportion of the noncoal minerals in the lungs was usually higher than it had been in the mine dust. This indicated some form of differential retention of these components, which was progressively more marked in men with the more serious grades of pneumoconiosis.

Right ventricular hypertrophy in a group of coalworkers.

The prevalence of right ventricular hypertrophy was studied in necropsy material from 215 coalworkers, a group which consisted of 115 men with simple or no pneumoconiosis and 100 with progressive massive fibrosis. Right ventricular hypertrophy was considered to be present if the ratio of the weight of the left ventricle plus septum to that of the right ventricle was less than 2:1. The prevalence of right ventricular hypertrophy was low (15%) in the absence of progressive massive fibrosis and appeared to be related to emphysema or airways disease or both, and not to simple pneumoconiosis. It was evident only in subjects who had smoked. In subjects with progressive massive fibrosis the prevalence of right ventricular hypertrophy was higher (34%) and it was occasionally seen in non-smokers. The prevalence increased with increasing size of lesion, and for any given size of lesion subjects with right ventricular hypertrophy had more panacinar emphysema than those without right ventricular hypertrophy. There was no relationship, however, between the extent of massive lesions or amount and type of emphysema and the degree of right ventricular hypertrophy.

Bronchial gland dimensions in coalminers: influence of smoking and dust exposure.

Bronchi from 94 coalminers were examined for enlargement of the mucous glands. The measurements used were the mean and maximum ratios of gland thickness to wall thickness, the mean acinar diameter, and the ratio of the gland area to the area of the non-cartilaginous portion of the bronchial wall. The relationships between these measurements and the subjects' smoking habits and their past exposure to dust in the coal mines were analysed. Smoking was found to be significantly related to mean and maximum gland-to-wall ratios. In addition, coalmine dust exposure was found to be significantly related to maximum gland:wall ratio. No significant relationships were found between gland dimensions and pneumoconiosis or dust retained in the lung. These results lend support to the view that irritants encountered in an occupational environment may play an important part in the development of hypersecretion of mucus.

Quantitative study of bronchial mucous gland enlargement.

Histological sections from 30 lower lobe bronchi, taken from coalminers' lungs collected for the British National Coal Board's Pneumoconiosis Field Research, were selected according to the proportion of mucous gland area occupying the non-cartilaginous part of the bronchial wall. The total gland area expressed as a percentage of the non-cartilaginous wall was called the gland index. Estimations were made of the total number of gland cells and acini on a section and of their numbers per unit area of gland. These estimations were compared with the gland index. The total numbers of gland cells and acini were found to be directly related to the gland index (r=0.84 and 0.86), whereas no relationship was found between the number of gland cells or acini per unit area of gland and the gland index (r=0.08 and 0.02). This indicates that bronchial mucous gland enlargement is primarily a hyperplastic change. A direct relationship between the numbers of gland cells per unit area of gland and acini per unit area gland was found (r=0.69), and this suggests that acinar enlargement is likely to be caused by accumulation of mucus in the acinar lumen.