Insulin differentially alters transcapillary movement of intravascular IGFBP-1, IGFBP-2 and endothelial cell IGF-binding proteins in the rat heart

Abstract

Insulin-like growth factor binding-proteins 1 and 2 (IGFBP-1, IGFBP-2) and endothelial cell IGF binding proteins (ECBP) were individually perfused through isolated beating rat hearts in the absence and presence of insulin. Insulin caused an increased movement of IGFBP-1 from the vascular space to tissues of the heart. Subendotheial content of IGFBP-1 was 110%, 126% (p < .01) and 132% (p < 0.05) of control hearts when perfused with 1, 10 and 100 ng/ml insulin, respectively. In contrast, insulin treatment was associated with a decrease in ECBP content in cardiac tissue, being 83%, 62% (p < 0.005) and 73% (p < 0.05) of control when perfused with 1, 10 and 100 ng/ml insulin. The efflux of IGFBP-2 from the intravascular space was unaffected by insulin. The subendothelial tissue distribution of the transported binding proteins was not changed by insulin perfusion, with IGFBP-1 and IGFBP-2 localizing predominantly in cardiac muscle and ECBP having greater affinity for connective tissue elements. We conclude that in the perfused rat heart, insulin can differentially alter transcapillary movement of IGFBP-1, IGFBP-2 and endotheial cell IGF-binding proteins. Such insulin-facilitated changes could potentially mediate nutrient-dependent transport of IGF-I and IGF-II to peripheral tissues.