PLATELET-DERIVED GROWTH-FACTORS AND GROWTH-RELATED GENES IN RAT LUNG .3. IMMUNOLOCALIZATION DURING FETAL DEVELOPMENT

To further study the role of platelet-derived growth factor (PDGF) in fetal lung development, the distribution of the PDGF homodimers PDGF-A A and PDGF-BB was examined by immunohistochemistry in embryonic and fe tal rat lung from d 12 to 22 of gestation (term = 22 d). PDGF-AA and P DGF-BB were localized to airway epithelial cells as early as d 12 of g estation, 2 d before their appearance in mesenchymal cells. Both PDGF homodimer immunoreactivities increased until the late pseudoglandular stage of lung development, followed by fluctuations in reactivity duri ng the canalicular stage. Only weak immunoreactivity to either PDGF ho modimer was evident during the saccular stage of lung development. Imm unodetection by Western blotting revealed that PDGF-AA and PDGF-BB hom odimer protein concentrations were high during the embryonic and pseud oglandular stage of lung development and decreased with advancing gest ation. We conclude that the presence of PDGF in both developing airway epithelial cells and mesenchymal cells, as well as gestation-dependen t changes of PDGF homodimers, is compatible with a role for this growt h factor during fetal lung development.