Previous work in this laboratory has demonstrated increased secretion of
fibroblast growth factor (
MDGF) activity by alveolar macrophages obtained from mice with
bleomycin-induced
pulmonary fibrosis. The mechanism by which
bleomycin promotes this increase in
MDGF secretion is not clear, however. The purpose of this study was to determine the direct effects of
bleomycin on alveolar macrophages. Normal rat alveolar macrophages obtained by lavage were cultured in the presence or absence of
bleomycin;
conditioned media from these cultures were dialyzed to remove
bleomycin and then assayed in vitro for
MDGF activity. Alveolar macrophages incubated with 0.01 microgram to 1 microgram/ml
bleomycin for 18 hours secreted significantly more
MDGF than macrophages incubated without
bleomycin. Viability of macrophages as determined by exclusion of
trypan blue and release of LDH was unaffected by any dose tested. Maximal
MDGF production was seen with
bleomycin doses of greater than or equal to 0.1 microgram/ml. When alveolar macrophages were incubated with 0.1 microgram/ml
bleomycin for 0.5-18 hours,
MDGF activity was detected as early as 1 hour, with peak responses found at 4-8 hours. Macrophages stimulated with
bleomycin continued to produce significant amounts of
MDGF even after
bleomycin was removed and replaced with fresh (
bleomycin-free) media.
MDGF secretion by
bleomycin-stimulated alveolar macrophages was inhibited by
cycloheximide, and the
5-lipoxygenase inhibitors NDGA (nordihydroguairetic
acid) and
BW755c, indicating not only a requirement for
protein synthesis but also for metabolites of the
5-lipoxygenase pathway of
arachidonic acid metabolism for full expression of activity(ABSTRACT TRUNCATED AT 250 WORDS)