Maintenance of steroid metabolism in primary cultures of adult rat hepatocytes in serum-free medium

stimulated cells: 2.63.5 nmol/l O6 cells). The 0;production was dependent on the presence of oxidative substrates such as glucose and succinate. Mast cells, on the other hand, did not release 0;upon activation with IgE antibody or compound 48/80, although both the stimuli caused substantial release of histamine and serotonin. However, both mast cells and macrophages Benerated significant amounts of 0;upon activation by Ca-+ ionophore, A23 187. In mixed cell experiments, zymosan-induced measurable 0;release from macrophages was abolished when mast cells were simultaneously activated with compound 48/80. The abolishment of 0;generation was also noted when isolated mast cell granules or the granule extract was added to macrophages. The inhibition of 0;generation caused by mast cell granules and the granule extract was dose-dependent. The addition of mast cell granules equivalent of 1 x 106 mast cells to 5 x 10' macrophages completely abolished 0;; production. This indicated that mast cell granules may contain superoxide dismutase which when released into the medium scavenges 0;generated by macrophages. The presence of superoxide dismutase in the mast cell granules was further substantiated using the xanthine-xanthine oxidase system. These data confirm the previous work (Henderson & Kaliner, 1978) that superoxide dismutase is present in mast cell granules in abundant quantities. It was further noted that incubation of mast cell granules in Ca2+, Mg*+-rich medium did not release superoxide dismutase in the soluble form. This suggests that the enzyme remains bound to the granule and may require macrophage phagocytosis in order to modulate 0;generation. These results implicate the mast cell in the modulation of macrophage generation of O;-. This down-regulation of macrophage function by mast cells may have important implications in the prevention of 0; -mediated tissue injury.