Cortisol is the principal corticosteriod in teleost fishes and its plasma concentrations rise dramatically during stress. The relationship between this cortisol increase and its metabolic consequences are subject to extensive debate. Much of this debate arises from the different responses of the many species used, the diversity of approaches to manipulate cortisol levels, and the sampling techniques and duration. Given the extreme differences in experimental approach, it is not surprising that inconsistencies exist within the literature. This review attempts to delineate common themes on the physiological and metabolic roles of cortisol in teleost fishes and to suggest new approaches that might overcome some of the inconsistencies on the role of this multifaceted hormone. We detail the dynamics of cortisol, especially the exogenous and endogenous factors modulating production, clearance and tissue availability of the hormone. We focus on the mechanisms of action, the biochemical and physiological impact, and the interaction with other hormones so as to provide a conceptual framework for cortisol under resting and/or stressed states. Interpretation of interactions between cortisol and other glucoregulatory hormones is hampered by the absence of adequate hormone quantification, resulting in correlative rather than causal relationships.

Cortisol in teleosts: dynamics, mechanisms of action, and metabolic regulation

The insulin-like growth factor (IGF) system plays a central role in the neuroendocrine regulation of growth in all vertebrates. Evidence from studies in a variety of vertebrate species suggest that this growth factor complex, composed of ligands, receptors, and high-affinity binding proteins, evolved early during vertebrate evolution. Among nonmammalian vertebrates, IGF signaling has been studied most extensively in fish, particularly teleosts of commercial importance. The unique life history characteristics associated with their primarily aquatic existence has fortuitously led to the identification of novel functions of the IGF system that are not evident from studies in mammals and other tetrapod vertebrates. Furthermore, the emergence of the zebrafish as a preferred model for development genetics has spawned progress in determining the requirements for IGF signaling during vertebrate embryonic development. This review is intended as a summary of our understanding of IGF signaling, as revealed through research into the expression, function, and evolution of IGF ligands, receptors, and binding proteins in fish.

Insulin-like growth factor signaling in fish.

Insulin-like growth factor-I (IGF-I) is a mitogenic polypeptide that plays an essential role in the regulation of development and somatic growth of vertebrates, mainly by mediating growth hormone actions. It has clearly been established that the structure of IGF-I and its biological function has been highly conserved among vertebrates. In this paper, we review the recent developments in the molecular, biochemical, and physiological properties of IGF-I in fish.

https://www.jstage.jst.go.jp/article/bbb/64/8/64_8_1553/_pdf

Growth Regulation by Insulin-like Growth Factor-I in Fish

Roles of insulin-like growth factor (IGF) binding proteins in regulating IGF actions

This communication summarizes viewpoints, discussion, perspectives, and questions, put forward at a workshop on “Growthhormone and insulin-like growth factors in Wsh” held on September 7th, 2004, at the 5th International Symposium on Fish Endocri-nology in Castellon, Spain. 2005 Elsevier Inc. All rights reserved. Keywords: Growth Hormone and insulin -like growth factors in Wsh 1. Growth hormone Growth hormone (GH) is a pluripotent hormone pro-duced by the pituitary gland in teleosts as in other verte-brates. GH brings about its action by binding to a singlepass-transmembrane receptor, the GH receptor (GHR),in target tissue. Ligand binding induces receptor dimer-ization producing an active trimeric complex (for review,see Perez-Sanchez et al., 2002). GH has been sequencedand/or the protein isolated from scores of teleosts, vari-ous immunoassays established, and a number of GH-transgenic Wsh strains established. Over the last twodecades, many aspects of GH physiology have been thesubject of intense research in Wsh such as the salmonids,cyprinids, and sparids. In Wsh, GH participates in almostall major physiological processes in the body includingthe regulation of ionic and osmotic balance, lipid, pro-tein, and carbohydrate metabolism, skeletal and soft tis-sue growth, reproduction and immune function. Recentstudies have indicated that GH aVects several aspects ofbehaviour, including appetite, foraging behaviour,aggression, and predator avoidance, which in turn hasecological consequences (for reviews, see Bjornsson,1997; Bjornsson et al., 2004; Perez-Sanchez, 2000; Peterand Marchant, 1995).Despite the vast body of knowledge which exists doc-umenting GH action in teleost Wsh, the mode of GHaction remains a major discussion topic (for review, seeBjornsson et al., 2004). Generalized claims have beenmade that most/all GH eVects are indirect, based on anoutdated mammalian view where the pituitary/hepaticGH/IGF-I system was seen as an “axis” with IGF-Imediating the physiological action of GH (for review,see Bjornsson et al., 2004; Butler and Le Roith, 2001).

/pdf/growth-hormone-and-insulin-like-growth-factors-in-wsh-where-2c8olw461n.pdf

Growth hormone and insulin-like growth factors in Wsh: Where we are and where to go

The insulin-like growth factors (IGF) are evolutionarily ancient growth factors present in all vertebrates. The central importance of IGF for normal development and growth has been illustrated by the severe growth-retarded phenotype exhibited by IGF-I, IGF-II or IGF-I receptor knockout mice. Although we know much about the gross effects of IGF on the overall size of the fetus and the clinical manifestations that result from fetal and neonatal deficiency of IGF (i.e., severe growth retardation leads to dwarfism), very little is known about the in vivo actions of IGF during embryogenesis at the cellular and molecular levels. Most research on the developmental role of IGF has relied on rodent models, and attempts to elucidate the molecular and cellular basis of IGF actions have been hampered by the inaccessibility of the mammalian fetus enclosed in the uterus. During the past decade, there has been growing support for the concept that the IGF have been highly conserved in all vertebrates. Both IGF-I and IGF-II are present in fish, and their structures are highly conserved. Human and fish IGF-I are equally potent in mammalian and fish bioassay systems. Insulin-like growth factor mRNA is found in all life stages of fish, ranging from unfertilized egg to adult. The temporal and spatial expression pattems of fish IGF-I seem to be similar to those in mammals. Nutritional status and growth hormone both have a profound effect on IGF-I expression in fish, as they do in mammals. These features suggest that the IGF system is highly conserved between teleost fish and mammals. Because fish embryos develop extemally, they provide excellent animal models for understanding the regulatory roles of IGF, IGF receptor and IGF-binding proteins in vertebrate embryonic development. Current research on the developmental and nutritional roles of IGF in fish will undoubtedly contribute to knowledge of the basic physiology of vertebrates in general.

Nutritional and developmental regulation of insulin-like growth factors in fish : Nutritional and developmental roles of insulin-like growth factors between species

C. Duan

Papers

Nutritional and developmental regulation of insulin-like growth factors in fish : Nutritional and developmental roles of insulin-like growth factors between species