Comparisons of reactivity of pulmonary vascular and airway smooth muscle of sheep and calf to tryptamine analogues, histamine, and antigen.

Serotonin (5-hydroxytryptamine) contracted the pulmonary artery, trachea, and bronchus in both cattle and sheep. Serotonin contracted the calf pulmonary vein, but it relaxed the pulmonary vein of sheep. Histamine constricted the 2 pulmonary blood vessels and trachea in calves and sheep. In contrast, histamine relaxed the ovine bronchus, but not the bronchus of the calf. Antigen (equine serum) constricted pulmonary veins from sensitized calves, but relaxed pulmonary veins from similarly sensitized sheep. Apparently, sheep are naturally more resistant than calves to both histamine and serotonin which contribute to the pulmonary inflammatory reaction.