Characterization of intensely fluorescent cells in the liver of the rat. i. Histochemistry and 48/80-induced degranulation.

The nature of the intensely fluorescent cells (IFC) in the livers of male Sprague-Dawley rats was evaluated using histochemical and pharmacological techniques. The number and distribution of IFC in portal areas were quantified using some of these techniques. Cells which were metachromatic as well as fluorescent for serotonin, histamine, and heparin were observed in the connective tissue of the portal space, hilus, and capsule of the liver. Cells with the characteristics of chromaffin, enterochromaffin, or enterochromaffin-like cells were not seen in these locations. Intravenous administration of compound 48/80 a known mast cell degranulator, caused a significant decrease in the number of fluorescent and metachromatic cells in the portal areas of the liver. However, no significant difference was found in the number of cells counted in either the 48/80 or control groups when comparing the data from several histochemical methods. These results provided evidence that: (1) IFC demonstrate both fluorescence and metachromasia and, therefore, are mast cells, (2) compound 48/80 causes a comparable decrease in the number of serotonin and histamine fluorescent as well as metachromatic cells, indicating concomitant rather than differential release of serotonin, histamine, heparin, and/or other metachromatic substances, and (3) each of the three histochemical methods appears of equivalent sensitivity when used to study the effect of various factors (i.e., 48/80) on the release of endogenous substances from IFC. The results of this study indicate that the effects of 48/80 in vivo might be mediated through the release of various vasoactive substances from these IFC (mast cells).