Ornithine decarboxylase and histaminase (diamine oxidase) activities in rat thymus and their relationship to the thymus lymphocyte

Abstract

Two enzymes associated with the synthesis and degradation of polyamines, ornithine decarboxylase and diamine oxidase (histaminase), were found in high levels in rat thymus. The ornithine decarboxylase and, to a smaller extent, the histaminase activity declined with age or upon depletion of thymus of its lymphocytes by treatment with dexamethasone. The ornithine decarboxylase activity was located exclusively in the lymphocytes and the histaminase activity was located outside the lymphocytes in the surrounding thymus stroma. Studies with labeled precursor, dl-[2- 14C]ornithine, in vitro showed that the amino acid was taken up by the isolated thymus lymphocytes and was converted to [ 14C]putrescine, the first of the amines in the polyamine metabolic pathway. The labeled putrescine accumulated in the cell and did not diffuse readily in or out of the cell. It is suggested that the ability of the thymus lymphocytes to synthesize polyamines may be related to their capacity to proliferate at a rapid rate in thymus. These cells may serve, therefore, as a useful model to study the role of polyamines in cell and tissue growth.