LIGHT-MICROSCOPIC IMMUNOLOCALIZATION OF FIBROBLAST GROWTH-FACTOR-I AND GROWTH-FACTOR-2 IN ADULT-RAT KIDNEY

The fibroblast growth factors (FGFs) are a family of conserved polypep tides known to regulate cell differentiation and proliferation. We hav e used avidin-biotin-enhanced indirect immunohistochemistry to localiz e FGF-1 and FGF-2 in the rat kidney. The most consistent specific immu nostaining pattern is found in paraffin sections from kidneys perfusio n-fixed with 4% paraformaldehyde in 0.1 M phosphate buffer. Intracellu lar immunoreactivity for FGF-1 and FGF-2 is co-localized in visceral ( podocytes) and parietal (Bowman's capsule) glomerular epithelial cells , S-3 segments of proximal tubules, distal tubules and collecting duct s in the cortex, and thick ascending limbs and collecting ducts in the medulla. Immunoreactivity is also observed within urothelium and the tunica adventitia of large blood vessels. No immunostaining is found i n cortical S-1 or S-2 segments of proximal tubules, in frozen sections prepared from unfixed or 4% paraformaldehyde perfusion-fixed kidneys, or in paraffin sections from Bouin-fixed kidneys. Immersion fixation with 4% paraformaldehyde gives a similar staining pattern in paraffin sections to that achieved with perfusion fixation. However, in paraffi n sections fixed with methyl Carnoy's fixative, immunoreactivity is pr imarily localized to the tunica media of blood vessels, with little tu bular or glomerular immunostaining. Thus, variation in immunolocalizat ion patterns for FGFs can be partially attributed to differences in fi xative, preparative technique and antibody specificity.