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Structural and biochemical changes in lungs of 3-methylindole-treated rats
L W Woods1, D W Wilson, M J Schiedt
1Department of Veterinary Pathology, School of Veterinary Medicine, University of California, Davis 95616.
Abstract:
Effects of a single dose of 3-methylindole (3-MI) (250 mg/kg intraperitoneally) were studied at different times ranging from 12 hours to 2 weeks post-treatment (PT). Microscopic study revealed mild Clara cell injury 24 hours PT and mucus hyperplasia 24 hours to 2 weeks PT. Diffuse type I alveolar epithelial cell necrosis occurred at 48 hours, followed by type II cell hyperplasia. Septal edema and accumulation of interstitial and capillary polymorphonuclear leukocytes and perivascular mixed mononuclear inflammatory cells accompanied the injury and repair. A gradual resolution of lesions with persistent mononuclear inflammatory cellular clusters at septal junctions, focal septal fibrosis, and accumulation of alveolar macrophages was evident at 1 and 2 weeks PT. Collagen, measured as hydroxyproline, in 3-MI-treated rats was significantly increased to 130% and 139% of control (3.0 mg/lung) at 1 and 2 weeks PT, respectively. Biphasic peaks of plasma 6-keto-prostaglandin F1 alpha occurred at 12 to 24 hours and at 96 hours PT with 3-MI and thromboxane B2 was elevated 12, 48, and 96 hours PT. Right ventricular/left ventricular and septal weight was increased to 120% and 140% of the control 1 and 2 weeks PT. We concluded that 3-MI induces alveolar septal injury in the rat with relatively complete repair of the alveolar epithelium and residual mild focal septal fibrosis and pulmonary hypertension 2 weeks PT. Arachidonic acid-derived mediators and inflammation are associated with 3-MI-induced lung injury.
Insights
A single dose of 3-methylindole (3-MI) causes lung injury in rats, leading to inflammation, fibrosis, and pulmonary hypertension. While alveolar repair occurs, some scarring and elevated blood pressure persist two weeks post-treatment.
Area of Science:
- Pulmonary Toxicology
- Pathology
- Pharmacology
Background:
- 3-methylindole (3-MI) is a known lung toxicant.
- Understanding the temporal progression of 3-MI-induced lung injury is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the pathological and biochemical effects of a single dose of 3-methylindole (3-MI) on rat lungs over a two-week period.
- To characterize the inflammatory response, tissue repair, and development of pulmonary hypertension following 3-MI exposure.
Main Methods:
- Rats received a single intraperitoneal dose of 3-MI (250 mg/kg).
- Lung tissues were examined microscopically at various time points (12 hours to 2 weeks).
- Collagen content (hydroxyproline), plasma prostaglandin and thromboxane levels, and cardiac weight ratios were measured.
Main Results:
- 3-MI induced Clara cell injury, mucus hyperplasia, and alveolar epithelial cell necrosis, followed by repair and hyperplasia.
- Inflammation, characterized by leukocyte infiltration and macrophage accumulation, was observed.
- Increased collagen deposition, elevated prostaglandin and thromboxane B2 levels, and right ventricular hypertrophy indicated lung fibrosis and pulmonary hypertension.
Conclusions:
- 3-MI causes significant alveolar septal injury in rats.
- The injury involves inflammation and arachidonic acid-derived mediators.
- While alveolar repair is relatively complete, residual mild fibrosis and pulmonary hypertension persist at two weeks post-treatment.