PULMONARY EFFECTS OF RICIN IN THE ISOLATED PERFUSED RAT LUNG MODEL

Abstract

The isolated perfused lung model consists of a temperature controlled chamber with reservoirs, tubing and a small animal respirator, capable of maintaining freshly excised lungs in a viable condition for several hours. It is a flexible system that allows for different routes of exposure and/or treatments of toxins or drugs under study. It also allows for a wide variety of parameters to be measured as indicators of tissue damage and effects of the toxin studied. Isolated perfused rat lungs were used to study pulmonary effects of ricin, a toxic lectin isolated from the castor bean Ricinus communis, Euphorbiaceae (Funatsu, 1972). Several test agents used in the preliminary evaluation of the system were hydrochloric acid (HC1), 4β,15-diacetoxy 3α-hydroxy-8α-(3-methylbutyrryloxy)-12,13-epoxytrichothec-9-ene (T-2), microcystin (MCYST) and ethanol (Et0H). Ricin and test agents were delivered to the isolated rat lung by the intravascular route (perfusate) or by intratracheal instillation. Glucose utilization, lactate production, and enzyme (LDH and AST) release into perfusate indicated lung function and tissue damage. Control lungs used 47.8 ± 3.33 μmol/g lung/hr of glucose and converted 37% to lactate. Exposure of the isolated lung, through either the intravascular or intratracheal route, to HC1, MCYST and T-2 appeared to increase the release of LDH. Lungs exposed to HC1 and Et0H through the intravascular route and to T-2 through the intratracheal route showed a a trend towards greater use of glucose than controls. Lungs exposed to ricin through the intravascular route significantly increased release of LDH, but not ricin (500 μg/kg) through the intratracheal route. The lung exposed to ricin B chain appeared to show a greater release of LDH and AST but lower utilization of glucose. Exposure of the isolated lung to ricin tended to increase the release of acid phosphatase and 6-ketoPGFᵢₐ, while the release of thromboxane and PGE2 did not seem to be increased. Light microscopy showed changes, such as lymphoid necrosis in the bronchiole-associated lymphoid tissue in the lung after exposures to ricin, through both routes, and to T-2, that were not seen in any of the control lungs, but the significance of these changes are unknown since they were not seen in all lungs. Perivascular edema and bronchiectasis seen in some control lungs indicated that further modifications of the system are necessary. Use of an immunogold staining technique provided useful insight to the distribution of ricin through the different routes. Preliminary studies with FITC-ricin provided some information on the distribution of the toxin and the differences to exposure through the intravascular versus the intratracheal route. These preliminary results show that the isolated perfused rat lung model is a valuable tool in the study of pulmonary effects of toxins on this organ.