IGF-I and IGFBP-3 transport in the rat heart

Abstract
Specific binding of IGF-binding protein (IGFBP)-3 was shown to be present in the isolated, beating rat heart. The uptake of perfused 125I-labeled IGF-I in the beating heart was decreased to 9% by blocking IGF-I binding sites with the IGF-I analog Long R3 (LR3) IGF-I. When LR3 was perfused with complexes of125I-IGF-I · IGFBP-3, uptake of125I-IGF-I was decreased to 41%, which was significantly greater than LR3 and 125I-IGF-I (41 vs. 9%). These data suggest that both microvessel IGF-I and IGFBP-3 binding sites contribute to the transport of IGF-I in the perfused rat heart. This also suggests a novel and plausible mechanism whereby circulating IGFs reach sites of IGF bioactivity.

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