Modulation of macrophage arginase gene expression and activity by progesterone

The influence of the pregnancy hormone progesterone on macrophage activation is well studied due to the existence of macrophages within the female reproductive tract and uterus during pregnancy. The production of nitric oxide (NO) from L-arginine, occurs via the action of the enzyme nitric oxide synthase-2 (NOS2) and can be induced experimentally by LPS. Progesterone downregulates NO production through binding the glucocorticoid receptor, in order to limit infl ammation. Arginase I also uses L-arginine as a substrate resulting in the production of L-ornithine and urea as a by-product. Induction of arginase I is typically associated with stimulation with the Th2 associated cytokines IL-4 and IL-13. The aim of this work was to investigate the ability of progesterone to modulate arginase gene expression and enzyme activity in murine macrophages.