Serum histamine levels following administration of ultrastructural tracers in three strains of rats.

Intravenous administration of the electron-opaque tracer ferritin resulted in substantial elevation of serum histamine levels in both the Munich--Wistar and Wistar-Furth strains of albino rats. Lewis rats were unaffected. Similarly, infusion of the non-protein tracer dextran was followed by greatly elevated serum histamine concentrations in Munich-Wistar and Lewis, but not in Wistar-Furth, rats. In sharp contrast with these results were those obtained using the tracer polyvinylpyrrolidone (PVP). PVP infusion caused no elevation of serum histamine levels in any of the rat strains studied. Caution in the use of such tracers is thus advised, since serum histamine concentration affects vascular permeability. Careful matching of ultrastructural tracer and strain of experimental animal is prerequisite in permeability studies.