Fluorometric determination of peripheral tissue histamine levels using Bio-Rex 70

Bio-Rex 70, a weak cation exchange resin, has been incorporated into a column chromatographic extraction procedure for the determination of peripheral tissue levels of histamine. The extracted histamine is quantified fluorometrically after condensation with o-phthaldialdehyde (OPT). The sensitivity of the procedure allows for the chromatographic extraction, using Bio-Rex 70, of 10 ng histamine to give fluorescence twice that of the blank. Because this extraction procedure does not separate histamine from spermidine it cannot be applied in determining levels of brain histamine. However, because spermidine in concentrations of up to 400 times that of histamine does not interfere with OPT-histamine fluorescence, the histamine levels of all peripheral tissues (including nerves) and fluids may be confidently examined. The relative simplicity of the procedure allows for the determination of 30 tissue samples within a working day. The method has been applied to determine peripheral tissue levels of histamine in naïve Wistar rats and the effects of compound 48/80 on these levels in several selected tissues have been investigated. Compound 48/80 decreased the levels of histamine in the heart, kidney and ileum, whereas these levels were initially elevated in the liver and lung without subsequent depletion. Since the reliability of existing histamine extraction procedures is questionable under certain conditions, it is suggested that the use of Bio-Rex 70 is a valuable addition in evaluating the possible physiological role(s) of tissue histamine.