A modified method for the isolation and determination of brain histamine using the Bio-Rex 70.

Bio-Rex 70, a weak cation exchange resin, has been used to specifically isolate histamine from rat brain tissue. This method compares favourably to other extraction procedures with respect to selectivity, reproducibility and time taken to perform the procedure. However, because it combines the optimum of these properties, it appears more adaptable for routine laboratory use. Following isolation, histamine is quantified fluorometrically after condensation with o-phthaldialdehyde (OPT). The sensitivity of the procedure allows for the chromatographic isolation, using Bio-Rex 70, of 12.5 ng histamine to give fluorescence twice that of blank. In addition, the use of Bio-Rex 70 enables the selective separation of histamine from fluorescent contaminants such as spermidine. The stability and the reproducibility of the adsorption and elution characteristics of Bio-Rex 70 enables the determination of 30 brain samples in a working day. This method has been applied to determine whole brain and regional brain levels of histamine in control and L-histidine-treated rats. The whole brain level of histamine, which was 50 ng/g, was increased by L-histidine and the highest concentration of histamine was found in the hypothalamus. 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 of brain histamine.