Submitted to: Domestic Animal Endocrinology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/2/2004
Publication Date: 2/5/2005
Citation: Small, B.C., Peterson, B.C. 2005. Establishment of a time-resolved fluoroimmunoassay for measuring plasma insulin-like growth factor I (IGF-I) in fish: effect of fasting on plasma concentrations and tissue mRNA expression of IGF-I and growth hormone (GH) in channel catfish (Ictalurus punctatus). Domestic Animal Endocrinology 28:202-215. Interpretive Summary: Insulin-like growth factor-I (IGF-I) mediates many of the growth promoting actions of growth hormone (GH) and is a potential candidate gene for fish growth. A time-resolved fluoroimmunoassay (TR-FIA) for measuring blood concentrations of IGF-I was established and validated in three domestically cultured fishes, channel catfish, hybrid striped bass, and rainbow trout. The IGF-I TR-FIA is sensitive, accurate, and precise for all three species of fishes, and provides a low-cost, non-radioisotopic method for quantifying plasma IGF-I levels. Validation of the IGF-I TR-FIA is a crucial step toward defining the role of IGF-I in fish.
Technical Abstract: A time-resolved fluoroimmunoassay (TR-FIA) was established and validated that allows for the determination of plasma concentrations of insulin-like growth factor I (IGF-I) in three domestically cultured fishes, channel catfish (Ictalurus punctatus), hybrid striped bass (Morone chrysops x M. saxatilis), and rainbow trout (Oncorhynchus mykiss). Sensitivity of the assay was 0.20 ng/ml. Intra- and inter-assay coefficients of variation (CV) were < 7 and < 12%, respectively. Serial dilutions of plasma from each species were parallel to the standard curve. Recovery of IGF-I from spiked plasma samples was > 90% for all three species of fishes. The IGF-I TR-FIA was biologically validated via its use to determine the effect of fasting on circulating IGF-I levels in channel catfish. Fasting-induced changes in plasma growth hormone (GH), hepatic IGF-I mRNA expression, and pituitary GH mRNA expression were also determined. Fasted channel catfish lost 5.6 and 15.6% body mass after 2 and 4 weeks of fasting, respectively. Plasma IGF-I concentrations were depressed (P < 0.05) relative to fed controls following 2 and 4 weeks of fasting. Plasma GH concentrations were not different (P > 0.05) in fasted fish after 2 weeks, but significantly increased (P < 0.05) by 4 weeks of fasting. Hepatic IGF-I mRNA expression after 2 and 4 weeks of fasting was reduced (P < 0.05) relative to fed controls. Pituitary GH mRNA expression was similar (P > 0.05) between 2-week fasted catfish and fed controls, but was increased (P < 0.05) in 4-week fasted catfish. The IGF-I TR-FIA was sensitive, accurate, and precise for all three species of fishes, and provided a low-cost, non-radioisotopic method for quantifying plasma IGF-I levels in fed and fasted channel catfish.