Macrophages as a major source of oxygen radicals in the hyperoxic newborn rat lung

The lungs of newborn rats exposed to 60% O-2 for 14 d were found to have a greatly increased cyanide-insensitive O-2 consumption, reflecting increased reactive oxygen species (ROS) formation. Exposure of the lung to hyperoxia is known to increase the production of ROS by mitochondria. We hypothesized that macrophages may also be a major contributor to this increase. Newborn rat pups were exposed to either air or 60% O-2 for 14 d and received either intraperitoneal gadolinium chloride (GdCl3) to abrogate macrophage influx, or inert vehicle. Lung homogenates were equilibrated in either 21% or 100% O-2 and total and cyanide-insensitive O-2 consumption, as well as nitric oxide accumulation were measured polarographically. Citrate synthase, a marker of mitochondrial mass, and nitrotyrosine, a marker of peroxynitrite formation, were quantified by Western blot. In addition to increased macrophage numbers, the lungs of 60% O-2-exposed animals had greatly increased cyanide-insensitive O-2 consumption (p <.05 compared to air controls) and immunoreactive nitrotyrosine (p <.05), which were all completely abrogated by treatment with GdCl3. Exposure to 60% O-2 for 14 d had no effect on peroxynitrite-independent nitric oxide release or mitochondrial mass. We conclude that increased ROS in the lungs of newborn rats exposed to 60% O-2 for 14 d was likely to be caused, in significant part, by the presence of increased numbers of macrophages. (C) 2003 Elsevier Inc.