Degranulation of endothelial specific granules of the toad aorta after treatment with compound 48/80

Incubation of isolated toad aortas in Ringer solution containing compound 48/80, a histamine liberator, resulted in marked degranulation of endothelial specific granules. Since incubation of these vessels in Ringer solution only did not show significant morphologic changes in these granules, these findings suggest that the degranulation was induced by histamine release from the granules, as in the case for mast cell degranulation, and that endothelial specific granules are a storage site of histamine in the toad aorta. The present morphologic data were supported by preliminary chromatography, which showed appreciable concentrations of histamine in the granule-containing pellets of subcellular fractions of homogenized toad aortas.