Changes in the pulmonary uptake and binding of drugs in an experimental model of lung fibrosis

Methods for the study of lung metabolism

The recognition of the non-respiratory functions of the lung has led to an increased interest in pulmonary metabolism. The practical methods used to study metabolism in other tissues have all been applied to the investigation of lung metabolism. Methods fall into two groups: those used in vivo and those used in vitro after disrupting the organ or isolating it from other tissues and perfusing its circulation. Some of the methods used in vitro disturb the tissue environment in such a way as to introduce experimental artifacts which make the interpretation of results difficult. There are advantages to the use of the isolated perfused organ technique which, although it has been established for many years, has recently been improved. This method lends itself particularly well to studies of the intermediary metabolism and uptake of drugs by lung tissue. These improvements are described and the application to pulmonary drug uptake is illustrated by reference to the drug mexiletine. The relative advantages of the various methods and their applications are discussed.

Lung function and airway inflammation in rats following exposure to combustion products of carbon-graphite/epoxy composite material: comparison to a rodent model of acute lung injury

Pulmonary function and inflammation in the lungs of rodents exposed by inhalation to carbon/graphite/epoxy advanced composite material (ACM) combustion products were compared to that of a rodent model of acute lung injury (ALI) produced by pneumotoxic paraquat dichloride. This investigation was undertaken to determine if short-term exposure to ACM smoke induces ALI; and to determine if smoke-related responses were similar to the pathogenic mechanisms of a model of lung vascular injury. We examined the time-course for mechanical lung function, infiltration of inflammatory cells into the lung, and the expression of three inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha), macrophage inflammatory protein-2 (MIP-2) and interferon-gamma (IFN-gamma). Male Fischer-344 rats were either exposed to 26.8-29.8 g/m(3) nominal concentrations of smoke or were given i.p. injections of paraquat dichloride. Measurements were determined at 1, 2, 3, and 7 days post exposure. In the smoke-challenged rats, there were no changes in lung function indicative of ALI throughout the 7-day observation period, despite the acute lethality of the smoke atmosphere. However, the animals showed signs of pulmonary inflammation. The expression of TNF-alpha was significantly increased in the lavage fluid 1 day following exposure, which preceded the maximum leukocyte infiltration. MIP-2 levels were significantly increased in lavage fluid at days 2, 3, and 7. This followed the leukocyte infiltration. IFN-gamma was significantly increased in the lung tissue at day 7, which occurred during the resolution of the inflammatory response. The paraquat, which was also lethal to a small percentage of the animals, caused several physiologic changes characteristic of ALI, including significant decreases in lung compliance, lung volumes/capacities, distribution of ventilation, and gas exchange capacity. The expression of TNF-alpha and MIP-2 increased significantly in the lung tissue as well as in the lavage fluid. Increased MIP-2 levels also preceded the maximum neutrophil infiltration. The differences in the time-course and primary site of TNF-alpha, MIP-2, and IFN-gamma expression; and the differences in the temporal relationship between their expression and infiltration of inflammatory cells may have accounted for the differences in lung function between paraquat treated and ACM smoke exposed animals.

Paraquat-induced, dose-dependent conditioned taste aversions and weight loss mediated by the area postrema

Paraquat's (PQ) effect on feeding behavior in the rat was examined using a conditioned taste aversion (CTA) paradigm. CTA is a learned avoidance of tastes closely associated with prior illness. Male Sprague-Dawley rats trained to drink an instant breakfast solution were subsequently offered a novel-flavored solution and consumption was measured over 30 min. Following consumption of the novel solution, PQ (0.48-48.0 mumol/kg) was injected subcutaneously. Peak blood PQ concentrations were measured by serially sampling blood (0.15 ml) from an indwelling jugular cannula between 10 and 35 min after injection. Two days later, the rats were offered the same novel-flavored solution. Paraquat produced dose-dependent avoidance of the novel solution when injected subcutaneously. A PQ dosage of 2.7 mumol/kg or less did not alter consumption. The ED50 for CTA production of 13.0 mumol/kg was determined by log-probit analysis. The minimum effective dosage was 4.2 micron/kg. The doses examined did not produce overt clinical or histological signs of toxicity. Peak blood paraquat concentration was linearly related (r = 0.995) to dosage. Additionally when administered by gavage CTAs occurred only with a much larger PQ dosage (480 mumol/kg). Thermal lesions of a hindbrain circumventricular organ, the area postrema (AP), prevented PQ-induced CTAs despite repeated PQ injections. Additionally, weight loss following PQ exposure was also attenuated by AP lesions. CTAs were induced in these same AP-lesioned rats by oral administration of copper sulfate. This substance conditions taste aversions by activating vagal afferent neurons. The fact that copper sulfate-induced aversions were not blocked by lesions of the area posterema indicates that the lesioned rats are capable of forming CTAs when treated with a toxicant which does not act via the AP. These data indicate that PQ produces CTAs in a dose-dependent manner. Furthermore, PQ-induced CTAs and weight loss are mediated by the AP. The AP may contain receptors which detect xenobiotics, enabling animals to avoid future contact with these compounds.

Some new data to the toxicological effects of paraquat and the therapy

1. Substances previously tested therapeutically were studied to obtain evidence on the pathomechanism in mice of paraquat, the active ingredient of Gramoxon, connected with the radicals formed from molecular oxygen, and also to extend the therapeutic possibilities. 2. The effects of these substances were assessed on the basis of the 72-hr survival rate and the percentage ratio of the wet lung weight to the overall body weight. 3. Other toxicological parameters too were followed. 4. Our present investigations indicate that, in agreement with our earlier results, besides reduced glutathione and ascorbic acid, vitamin E and C-ase are of the greatest importance from the aspect of the protection against paraquat toxicity. 5. In addition to those listed, other materials too, e.g. antifibrotic substances, naturally possess considerable detoxicating properties too.