Immunohistochemical localization of basic and acidic fibroblast growth factors in the developing rat heart

We used biochemical and immunohistochemical techniques to investigate the expression and distribution of immunoreactive basic and acidic fibroblast growth factors (bFGF and aFGF, respectively) in the hearts of rat embryos (11-20 days of gestation) and of postnatal rats (1-35 days after birth). Our purpose was to assess the relation between the cellular distribution of these growth factors and histogenetic and morphogenetic events in the developing heart.

Western-blot analysis of heparin-bound material from neonatal heart extracts identified a single band with a molecular weight of approximately 18 kD for both bFGF and aFGF. Five antibodies for bFGF and three for aFGF showed superimposable distribution of immunoreactive bFGF and aFGF in the heart at each stage examined. At the cellular level, these peptides were localized in the cytoplasm and extracellular matrix. In the myocytes, immunostaining was positive throughout the embryonic and neonatal periods. In the majority of the mesenchymal cells of the cushions and endothelial cells of endocardium and vessels, staining was also positive. In the smooth muscle cells of the aorta, other large arteries, and coronary arteries, immunostaining was intensely positive at early stages of development but became faint or negative with increasing cell differentiation.

The wide distribution of immunoreactive bFGF and aFGF that we identified in the developing rat heart suggests that these growth factors play an important role in heart cytodifferentiation and morphogenesis. Their superimposable distribution may reflect functional interaction. The progressive changes in their distribution suggest a changing role for these peptides during organogenesis.