Disparate regulation of insulin-like growth factor-binding proteins in a primitive, ictalurid, teleost (Ictalurus punctatus) Jaime Johnson, a Jeffrey Silverstein, b,1 William R. Wolters, b Munetaka Shimizu, c Walton W. Dickhoff, c and Brian S. Shepherd a, * a Department of Biology, University of Kentucky, 101 T.H. Morgan Building, Lexington, KY 40506-0225, USA b USDA/ARS Catfish Genetics Research Unit, Stoneville, MS 38776, USA c Northwest Fisheries Science Center, National Marine Fisheries Service, Seattle, WA 98112, USA Accepted 12 June 2003 Abstract Vertebrate growth is principally controlled by growth hormone (GH) and, its intermediary, insulin-like growth factor-I (IGF-I). The actions of IGF-I are modulated by high-affinity binding proteins called insulin-like growth factor binding-proteins (IGFBPs). Channel catfish exhibit atypical responses (increased percentage body fat and reduced percentage protein) to GH treatment, despite GH-dependent IGF-I production. Among possible explanations for this atypical response to GH treatment is an unusual regulation of blood IGFBPs. In this species, there has been one report of a single 33-kDa plasma binding protein. To examine the occurrence and regulation of plasma IGFBPs in this species, two strains of channel catfish (Norris and USDA-103) were treated with weekly injections of recombinant bovine GH at different temperatures (21 °C versus 26 °C). In a separate experiment involving catfish of a different strain, endogenous GH levels were altered via injection of the GH secretogogue, bGHRH 1–29 -amide, and held in fresh water or transferred to brackish water (12 ppt). Following these treatments, the type and regulation of plasma IGFBPs in these catfish strains were examined by Western ligand blotting. We have identified five IGFBPs (19, 35, 44, 47, and >80 kDa) in catfish plasma that are differentially altered by experimental treatment and genetic lineage. Levels of the 19-kDa IGFBP were elevated in catfish of Norris and USDA-103 strains that were exposed to a higher environmental temperature (26 °C versus 21 °C), but was not seen in those animals used for the GH secretogogue/salinity study. In most vertebrates, treatment with GH increases levels of plasma IGFBP-3 (40–50 kDa). In the USDA-103 and Norris catfish strains, bGH injection reduced plasma levels of the 44- and 47-kDa IGFBPs. Similarly, elevations in plasma GH levels in GH secretogoge-treated and brackish water-adapted catfish resulted in re- ductions of the 44- and 47-kDa IGFBPs as well as a reduction in presence of a 35-kDa IGFBP that was not detected in the Norris or USDA-103 strains. Reduced levels of the 35, 44, and 47 kDa IGFBPs, seen in the plasma of the GH secretogogue-treated and brackish water-adapted animals, suggests that the atypical response of channel catfish to GH treatment is not attributed to the use of heterologous (bovine) GH. This negative response of the 35–47 kDa IGFBPs to GH has not been reported in any teleost or vertebrate (healthy) and may be partly responsible for the atypical physiological responses of channel catfish to GH treatment. Ó 2003 Elsevier Inc. All rights reserved. 1. Introduction Growth hormone (GH: including its receptor and binding protein), its anabolic intermediaries, the insulin- like growth factors-I and -II (IGF-I and -II), their high- affinity binding proteins (termed insulin-like growth factor binding proteins: IGFBPs) and the IGF-receptors constitute the vertebrate somatotropic axis. In the channel catfish (Ictalurus punctatus), growth hormone (GH) treatment (Silverstein et al., 2000; Wilson et al., 1988) elicits responses that are not characteristic to those seen in other vertebrates (Collier and Byatt, 1996) and, in some cases, can be deleterious (Kayes, 1977). The unusual response of channel catfish to GH treat- ment is similar to that of domestic fowl (Buyse and Decuypere, 1999) and the guinea pig (Keightley and Fuller, 1996) which both exhibit, to varying degrees, GH * Corresponding author. Fax: 1-859-257-1717. E-mail address: bsshep2@uky.edu (B.S. Shepherd). 1 Present address: USDA/ARS, National Center for Cool and Coldwater Aquaculture, Kearneysville, WV 25430, USA. www.elsevier.com/locate/ygcen General and Comparative Endocrinology 134 (2003) 122–130 GENERAL AND COMPARATIVE ENDOCRINOLOGY 0016-6480/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0016-6480(03)00244-2