Histamine and Heparin Release from Isolated Rat Mast Cells Exposed to Compound 48/80

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Abstract
The relationship between the release of histamine and heparin from rat mast cells exposed to compound 48/80 in vitro has been studied in order to elucidate the mechanism of action of this histamine releasing agent. Heparin is almost exclusively localized to the granule fraction of mast cells and therefore its release can be used as an index of granule release.The ratio percentage histamine release/percentage heparin release was found to be 1.4–1.7 and 1.6–2.0 following exposure of mast cells to 2.5 and 0.25 μg/ml respectively of compound 48/80. These “found” ratios are artificially high due to the fact that it is impossible to effect a complete separation of the released granules from the mast cells. Bearing this in mind, these results are consistent with the hypothesis (Uvnäs and Thon 1966) that the release of histamine‐containing granules is a primary event in the release of histamine induced by this agent. How ever, they do not exclude the possibility that part of the histamine release can take place without granule release. Studies of the specific activities of the 35S‐labelled heparin released and retained by mast cells taken from rats at different intervals after Na235SO4 injection and exposed to compound 48/80 suggest that the most mature granules are released first on treatment of mast cells with this substance.