Regulation of plasma insulin-like growth factor-I levels in brown trout (Salmo trutta)

Liver production of insulin-like growth factor-I (IGF-I) is a major point of control in the growth hormone (GH)/IGF axis, the endocrine system regulating body growth in fishes and other vertebrates. Pituitary GH stimulates hepatocyte production of IGF-I; however, in catabolic states, hepatocyte GH resistance results in decreases in liver IGF-I production. To investigate endocrine mechanisms leading to the development of hepatocyte GH resistance, we examined the regulation of IGF-I mRNA level by GH and metabolic hormones in primary culture of salmon hepatocytes. Cells were cultured in RPMI medium, and exposed to insulin (Ins, 10 6

Section: Discussionsupporting

confidence: 79%

Section: Discussionmentioning

confidence: 67%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Metabolic hormones modulate the effect of growth hormone (GH) on insulin-like growth factor-I (IGF-I) mRNA level in primary culture of salmon hepatocytes

Pierce

Fukada²,

Dickhoff³

2005

“…This may have been an indirect effect of insulin. In brown trout, insulin injection increased plasma Igf1 3 h later (Banos et al 1999), even though in coho salmon hepatocytes, insulin did not affect basal igf1 and suppressed GH-stimulated igf1 (Pierce et al 2005), suggesting that indirect stimulatory effects of insulin on liver Igf1 production may exist in salmonids. In this study, GH-stimulated hepatic igf2 mRNA levels to a biologically significantly greater degree than igf1 mRNA levels in vitro and in vivo, consistent with recent results in GH transgenic tilapia (Eppler et al 2010).…”

Section: Discussionmentioning

confidence: 87%

Differential regulation of Igf1 and Igf2 mRNA levels in tilapia hepatocytes: effects of insulin and cortisol on GH sensitivity

Pierce

Breves²,

Moriyama³

et al. 2011

Igf1 and Igf2 stimulate growth and development of vertebrates. In mammals, liver-derived endocrine Igf1 mediates the growth promoting effects of GH during postnatal life, whereas Igf2 stimulates placental and fetal growth and is not regulated by GH. Insulin enhances Igf1 production by the mammalian liver directly, and by increasing hepatocyte sensitivity to GH. We examined the regulation of igf1 and igf2 mRNA levels by GH, insulin, and cortisol, and the effects of insulin and cortisol on GH sensitivity in primary cultured hepatocytes of tilapia, a cichlid teleost. GH increased mRNA levels of both igf1 and igf2 in a concentration-related and biphasic manner over the physiological range, with a greater effect on igf2 mRNA level. Insulin increased basal igf2 mRNA level, and strongly increased GH-stimulated igf2 mRNA level, but slightly reduced basal igf1 mRNA level and did not affect GH-stimulated igf1 mRNA level. Cortisol inhibited GH stimulation of igf1, but increased GH stimulation of igf2 mRNA level. The synergistic effect of insulin and GH on igf2 mRNA level was confirmed in vivo. These results indicate that insulin and cortisol differentially modulate the response of igf1 and igf2 mRNA to GH in tilapia hepatocytes, and suggest that the regulation of liver Igf2 production differs between fish and mammals. Regulation of liver Igf2 production in fish appears to be similar to regulation of liver Igf1 production in mammals.

“…Consistent with this difference in IGFBP levels are the concentrations of IGF-I found in mammalian serum versus fish serum: in mammals, IGF-I typically circulates at levels between 500 and 800 ng/ml (e.g. Schmidt & Kelley 2001, discussed later), whereas in fish, serum IGF-I levels are typically 10-40 ng/ml, similar to insulin concentrations in both mammals and fish (see Baños et al 1999, Shimizu et al 2000, Larsen et al 2001. Similar findings have been reported in the toad, Bufo arenarum (Cortizo et al 1993).…”

Section: Circulating Igfbp-3-igf-i 'Reservoir': Are Mammals the Excepmentioning

confidence: 89%

Comparative endocrinology of the insulin-like growth factor-binding protein

Kelley¹,

Schmidt²,

Berg³

et al. 2002

105

Emerging early in chordate evolution, the IGF-regulatory axis diverged from an insulin-like predecessor into a vertebrate regulatory system specializing in cell growth activation and allied anabolic functions. Essential to the divergence of the IGF and insulin systems was an early presence of soluble IGF-binding proteins (IGFBPs), which bind IGF peptides at much higher affinity than that of the insulin receptor but at comparable affinities to that of the IGF receptor. IGFBPs have no homology with IGF receptors. Instead, IGFBPs are a derived group of proteins within a superfamily of cysteine-rich growth factors, whose members are found throughout the animal taxa. While blocking IGF actions through the insulin receptor is a fundamental role, IGFBPs evolved within the vertebrate line into centralized, 'integrators' of the endocrine growth-regulatory apparatus. IGFBPs have substantial influences on the distribution and bioavailability of IGF peptides in the cellular and physiological environments, but they have a variety of other properties. The six principal mammalian IGFBPs exhibit an array of specialized properties that appear to be derived from a complex evolutionary history (including cell membrane association, interaction with proteins that post-translationally modify them, direct IGF-independent effects on cells, and others) and they are regulated by a diversity of 'outside' factors (e.g. other hormones, metabolic status, stress). Thus, IGFBPs are multifunctional integrators having diverse physiological 'agendas'. Much less is known about IGFBPs and their properties in the other vertebrate taxa. Increasingly, however, it is being recognized that they play equally important endocrine roles, in both conserved and non-conserved ways, when compared with those currently defined in mammals. This review highlights selected 'comparative aspects' in current IGFBP research, in an attempt to view this essential group of endocrine regulators from a wider, biological perspective.