Measurement of circulating salmon IGF binding protein-1: assay development, response to feeding ration and temperature, and relation to growth parameters

Abstract

Fish plasma/serum contains multiple IGF binding proteins (IGFBPs), although their identity and physiological regulation are poorly understood. In salmon plasma, at least three IGFBPs with molecular masses of 22, 28 and 41 kDa are detected by Western ligand blotting. The 22 kDa IGFBP has recently been identified as a homolog of mammalian IGFBP-1. In the present study, an RIA for salmon IGFBP-1 was established and regulation of IGFBP-1 by food intake and temperature, and changes in IGFBP-1 during smoltification, were examined. Purified IGFBP-1 from serum was used for as a standard, for tracer preparation and for antiserum production. Cross-linking 125 I-labelled IGFBP-1 with salmon IGF-I eliminated interference by IGFs. The RIA had little cross-reactivity with salmon 28 and 41 kDa IGFBPs (<0·5%) and measured IGFBP-1 levels as low as 0·1 ng/ ml. Fasted fish had significantly higher IGFBP-1 levels than fed fish (21·6 4·6 vs 3·0 2·2 ng/ml). Plasma IGFBP-1 was measured in individually tagged 1-year-old coho salmon reared for 10 weeks under four different feeding regimes as follows: high constant (2% body weight/day), medium constant (1% body weight/day), high variable (2% to 0·5% body weight/day) and medium variable (1% to 0·5% body weight/day). Fish fed with the high ration had lower IGFBP-1 levels than those fed with the medium ration. Circulating IGFBP-1 increased following a drop in feeding ration to 0·5% and returned to the basal levels when feeding ration was increased. Another group of coho salmon were reared for 9 weeks under different water temperatures (11 or 7 C) and feeding rations (1·75, 1 or 0·5% body weight/day). Circulating IGFBP-1 levels were separated by temperature during the first 4 weeks; a combined effect of temperature and feeding ration was seen in week 7; only feeding ration influenced IGFBP-1 level thereafter. These results indicate that IGFBP-1 is responsive to moderate nutritional and temperature changes. There was a clear trend that circulating IGFBP-1 levels were negatively correlated with body weight, condition factor (body weight/body length 3 100), growth rates and circulating 41 kDa IGFBP levels but not IGF-I levels. During parr-smolt transformation of coho salmon, IGFBP-1 levels showed a transient peak in late April, which was opposite to the changes in condition factor. Together, these findings suggest that salmon IGFBP-1 is inhibitory to IGF action. In addition, IGFBP-1 responds to moderate changes in dietary ration and temperature, and shows a significant negative relationship to condition factor.

Postprandial changes in plasma growth hormone, insulin, insulin-like growth factor (IGF)-I, and IGF-binding proteins in coho salmon fasted for varying periods

“…For measurement of IGF-I, plasma IGF-I was extracted with an acid-ethanol and quantified by RIA as described in Shimizu et al (41) with recombinant salmon IGF-I (Novozymes, Adelaide, Australia) used as a tracer and standard. Plasma 41-kDa IGFBP and IGFBP-1 levels were measured by RIAs as described in Shimizu et al (39) and Shimizu et al (37), respectively.…”

“…Salmon 41-kDa IGFBP appears to be a functional homolog of IGFBP-3 (39), while its amino acid sequence is most similar to IGFBP-2 (36,42). These IGFBPs are under gross nutritional control (37,39). However, their overall physiological role and response to graded nutritional stimuli have not been fully examined in fishes.…”

Metabolic hormones regulate insulin-like growth factor binding protein-1 mRNA levels in primary cultured salmon hepatocytes; lack of inhibition by insulin

“…Medium IGFBP-1 protein levels were measured with a newly developed RIA (Shimizu et al 2006). Some nonparallelism was observed in serial dilutions of hepatocyte-conditioned medium versus assay standards and serial dilution of Chinook salmon serum (data not shown).…”

Effect of Culture Conditions on the Levels of Serum Insulin-like Growth Factor-1 in Indian Major Carps

“…A number of factors such as condition factor (Carlander, 1969), organosomatic indices (Goede and Barton, 1990), superoxides (Sahoo et al, 2005), insulin-like growth factor (IGF)-1, and IGF binding proteins (Picha et al, 2012) have been proposed to assess the growth potential and health of culturable species. Most of these regulatory events are mediated by the growth hormone (GH) and IGF axis (Pé rez-Sá nchez et al, 2002;Shimizu et al, 2006). The number of insulin and IGF receptors in fish is regulated by the nutritional status so that it can be altered according to the physiological need (Planas et al, 2000).…”

“…The number of insulin and IGF receptors in fish is regulated by the nutritional status so that it can be altered according to the physiological need (Planas et al, 2000). Reports are available on the levels of serum IGF-1 in different fish species such as chinook salmon Oncorhynchus tshawytscha (Beckman et al, 2004a;b), coho salmon O. kisutch (Pierce et al, 2004;Beckman et al, 2004a;b), Atlantic salmon Salmo salar (Dyer et al, 2004;Shimizu et al, 2006), tilapia Oreochromis mossambicus (Uchida et al, 2003), gilthead seabream Sparus aurata (Pé rez-Sá nchez et al, 1995;Mingarro et al, 2002;Gómez-Requeni et al, 2004;2005), channel catfish Ictalurus punctatus (Silverstein et al, 2000;Li et al, 2004) and Atlantic cod Gadus morhua (Davie et al, 2007). Li et al (2014) used transgenic crucian carp, Carassius auratus as the first teleost model to study the IGF-1 over expression in-vivo.…”