Generation of reactive oxygen species by polymorphonuclear leukocytes and its modulation by calcium ions during tumor growth

The generation of reactive oxygen species (ROS) by polymorphonuclear leukoc ytes (PMNL) and the role of Ca2+ in regulating their activity during Zajdel a hepatoma growth in the animal peritoneal cavity were studied. We found a marked increase in the ROS-generating activity of PMNL in circulating blood , the result of increases in both the specific activity of leukocytes and t otal number of PMNL in circulating blood. The ROS-generating activity of PM NL was substantially activated by Ca2+ ions and a calcium ionophore (ionomy cin), but this effect virtually completely disappeared during tumor growth. Perhaps the high ROS-generating activity of PMNL and the lack of the sensi tivity to extracellular Ca2+ during tumor growth in the organism are due to an accumulation of intracellular Ca2+ ions.