TRANSCAPILLARY PERMEABILITY AND SUBENDOTHELIAL DISTRIBUTION OF ENDOTHELIAL AND AMNIOTIC-FLUID INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEINS IN THE RAT-HEART

Insulin-like growth factor (IGF) binding proteins (IGFBP) were purified from conditioned media of cultured bovine endothelial cells (ECBP) and from human amniotic fluid (IGFBP-1), and then labeled by radioiodination.125I-ECBP and125I-IGFBP-1 were perfused through isolated beating rat hearts for 1 and 5 min, and the hearts fixed and analyzed for125I-BP content and distribution. One to 4% of the perfused125I-ECBP and125I-IGFBP-1 crossed the capillary boundary. The ECBPs predominantly localized as intact125I-BP in connective tissue elements of the heart with less125I-BP in cardiac muscle. The ratio of125I-ECBP in connective tissue: Muscle (normalized to percent vol of these compartments) was ≥10:l. In contrast, the IGFBP-1 had a greater affinity for cardiac muscle with ratios of125I-IGFBP-1 in connective tissue:muscle of approximately 1:2. When125I-IGF-I, in the absence of any BPs, was perfused through the hearts approximately 3-5% left the microcirculation and was found in subendothelial tissues.125I-IGF-I localized primarily to cardiac muscle with a distribution of connective tissue:cardiac muscle of about 1:3. The findings in the isolated perfused heart were confirmed in intact animals. After125I-IGFBP- 1 was injected into anesthetized rats and allowed to circulate for 5 min, substantial radioactivity was associated with the heart. As in the isolated heart, the IGFBP-1 preferentially localized to cardiac muscle with a connective tissuexardiac muscle ratio of 1:3. We conclude that IGFBPs produced by endothelial cells and the IGFBP-1 contained in amniotic fluid can cross the capillary boundaries of the rat heart, and that the ECBPs preferentially localize in connective tissue elements of the myocardium, whereas IGFBP-1 predominantly localizes in cardiac muscle. © 1990 by The Endocrine Society.