Distribution of mast cells and histamine in canine pulmonary arteries.

The distributions of mast cells and histamine along the canine pulmonary arterial tree were determined. Mast cell counts were made on toluidine blue stained histologic sections, and histamine concentration was measured in dissected arterial branches by an enzymatic-isotopic assay. Mast cell density and histamine concentration were greater in small muscular arteries compared to elastic arteries. In elastic arteries there was more histamine than would be expected by the number of mast cells found there, suggesting the presence of non-mast cell histamine in those vessels. In all arteries mast cells were located primarily in the adventitia. The finding of mast cells and histamine in greatest concentration in muscular pulmonary arteries suggests that these vessels are the major site of action of histamine and other mast cell contents within the pulmonary arterial tree.