Comparison of recombinant barramundi and human insulin-like growth factor (IGF)-I in juvenile barramundi (Lates calcarifer): In vivo metabolic effects, association with circulating IGF-binding proteins, and tissue localisation

The in vivo actions of human and fish insulin-like growth factor (IGF)-I ha ve been compared to extend the understanding of the metabolism of IGFs in f ish and to identify potential differences in their actions. The effects of acute administration of these proteins on the incorporation of glucose into muscle glycogen and leucine into liver protein in juvenile barramundi were investigated. In these in vivo metabolic assays, both baramundi IGF-I (bIG F-I) and human IGF-I (hIGF-I) increase the incorporation of D-[C-14]glucose into muscle glycogen and [C-14]leucine into liver protein. The distributio n of radio-labeled human and barramundi IGF-I in the circulation and their uptake by tissue was also compared in juvenile barramundi (Lates calcarifer ), Analysis of trichloroacetic acid-precipitable radioactivity in sequentia l samples following bolus injection of radiolabeled IGFs revealed that hIGF -I was degraded faster than bIGF-I. Neutral gel chromatography of these sam ples suggested that this difference is due to reduced affinity of hIGF-I, c ompared to bIGF-I, for the IGF-binding proteins (IGFBPs) present in the bar ramundi. Tissue uptake of [I-125]-labeled hIGF-I and bIGF-I was similar exc ept that [I-125]bIGF-I uptake by the kidney exceeded that of hIGF-I. It is suggested that while some of the in vivo actions of IGFs in fish are conser ved, functional differences between mammalian and teleostean IGFs exist, pa rticularly with respect to their interactions with fish IGFBPs. (C) 2000 Ac ademic Press.