Induction of pulmonary edema and emphysema in goats by intraruminal administration of 3-methylindole

Abstract

The effects of intraruminal administration of 3-methylindole (3MI; skatole) were determined in goats. The 3MI was given to 4 goats at the dose level of 0.3 g/kg of body weight, to 2 goats at 0.2 g/kg, and to 2 goats at 0.1 g/kg; 3 nontreated goats were used as controls. Clinical signs of acute progressive respiratory tract disease were seen in all treated goats. Goats given the largest dose of 3MI (0.3 g/kg) died between 5 and 11 hours after treatment; those given smaller doses (0.2 and 0.1 g/kg) died between 79 and 92 hours. Increased plasma concentrations of 3MI were detected in goats give 0.1 or 0.2 g/kg within 3 hours after administration. By 24 and 36 hours, the concentrations of 3MI in the plasma decreased to low or nondetectable amounts and remained low for the duration of the experiment. Clinical signs of respiratory distress in the goats progressed after 3MI had been cleared from the plasma. Diffuse pulmonary edema and hydrothorax were extensive in goats which died early in the course of the experimentally induced disease. In goats which died at later stages, the lungs were firm and had less watery transudate. Temporal variations in the nature of pulmonic changes were even more obvious by microscopic examination. Diffuse pulmonary edema was the predominant early change. Small foci of emphysema were apparently caused by overdistention of some clusters of alveoli. Marked septal thickening and proliferation of alveolar cells were the prominent changes in goats which died between 79 and 92 hours after treatment. Incubation of L-tryptophan with caprine ruminal fluid resulted in formation of indoleacetic acid, indole, and 3MI. Similar incubations did not convert indoleacetic acid to 3MI. Control incubations showed 3MI as a fermentation metabolite, indicating it exists in caprine ruminal fluid in vivo. Results demonstrated that goats are susceptible to intraruminal administration of 3MI. The transitory appearance of 3MI in the plasma associated with progressive respiratory tract disease was similar to observations in cattle give 3MI. Clinical signs and lesions seen at necropsy were qualitatively similar to those reported in cattle given tryptophan and indoleacetic acid.