Abstract
The spectrophotometric method for determination of histaminase, based on measurement of the hydrogen peroxide formed by the enzymatic oxidation of histamine, was modified and adapted to studies on microliter volumes of tissue (placenta) homogenates and microtome sections of tissue (human uterus and attached intact placenta at term). Optimal conditions for these assays were established. From analyses of tissue sections, peak enzyme activities were observed in the decidua, thus supporting the concept that this tissue is a significant source of the increased enzyme in blood plasma during pregnancy in the human. Inhibitor studies with aminoguanidine sulfate showed that the histaminase investigated in the human placenta was diamine oxidase. No histaminase activity was detected in isolated peritoneal mast cells from the rat or in homogenates of rat stomach mucosa.