Effects of 3-methylindole in cattle.

1 Rapid intravenous injection of 3-methylindole (3-MI) was shown to induce an anaphylactoid-like reaction in calves. 2 This was suggested by the reduction in response to a repeat dose of 3-MI, by the reduction of effects in the presence of antagonists to the putative mediators of anaphylaxis in cattle and by the production of signs similar to those seen in experimentally induced bovine anaphylaxis. 3 The plasma half-life of 3-MI was short (14.4 min) and, since absorption of 3-MI from the rumen is known to be slow, the extent of formation of 3-MI from L-tryptophan in the rumen would have to be substantial if 3-MI is to be considered the causative agent of 'fog fever', an acute respiratory distress syndrome seen in cattle.