Acute systemic anaphylaxis in the calf.

1. Acute systemic anaphylaxis in calves was characterized by marked systemic hypotension; hypertension in the pulmonary arteries and abdominal vena cava, and transient apnoea. Calves responded with a second reaction to antigen, but a third anaphylactic response could not be evoked.2. Suppression of systemic anaphylaxis could not be effected with mepyramine, whereas methysergide or diethylcarbamazine each suppressed anaphylaxis by 50%. Disodium cromoglycate alone did not inhibit anaphylaxis: however, when disodium cromoglycate was combined with diethylcarbamazine almost total suppression (85%) was achieved. Sodium meclofenamate also was a powerful inhibitor of anaphylaxis (80%). It is tentatively suggested that slow reacting substance (SRS-A) may be an important mediator of bovine anaphylaxis.3. Bilateral vagotomy did not modify the circulatory responses to injected histamine, 5-hydroxytryptamine (5-HT) or antigen, whereas the effects of these agents on ventilation (apnoea) were abolished by vagotomy.4. Plasma histamine concentration was increased during anaphylaxis, whereas plasma 5-HT was not. Whole blood histamine concentration fell sharply and remained depressed during 20 min of anaphylactic shock. Reduced whole blood histamine levels probably reflect the severe leucopoenia in the calves.5. Histamine concentrations in six tissues taken from calves subjected to anaphylaxis were not different from those in control calves; mast cells were of similar numbers to controls, but showed some swelling, granular spilling and metachromasia.6. Histamine, 5-HT, bradykinin and antigen caused increased pulmonary artery perfusion pressure and ventilation resistance in isolated lungs from sensitized calves. However, there was no difference in histamine and 5-HT concentration in perfusates obtained during antigen infusion of sensitized and control lungs.7. Systemic anaphylaxis of calves may result from the interaction of histamine, 5-HT and SRS-A. The present data implicate (by indirect measurement) SRS-A as an important mediator of anaphylaxis in this species.