T-cell receptor V beta gene segment expression in diisocyanate-induced occupational asthma

A simple and sensitive method for determining 5-aminolevulinic acid (ALA) in biological samples is described. ALA is derivatized with o-phthaldehyde to give a compound with favorable properties for high-performance liquid chromatography with electrochemical detection. The method does not require extensive pretreatment of the samples and its detection limit is in the range of 1 pmol/20 microl injection. This method was applied to the determination of plasma ALA from normal and lead-exposed subjects, where 0.26+/-0.08 microM (n=30) and 2.6+/-0.75 microM (n=30), respectively were found. We also determined ALA in rat tissues, namely liver and brain. and the uptake of ALA by cultured fibroblasts and hepatocytes to illustrate the diversified applicability of the method.