Influence of plasma lipid changes in response to 17β‐oestradiol stimulation on plasma growth hormone, somatostatin, and thyroid hormone levels in immature rainbow trout

Abstract

Plasma total lipids were significantly higher in 17 -oestradiol (E 2 )-treated immature rainbow trout Oncorhynchus mykiss at week 4 after implantation, due to increases in polar and neutral lipids. The lipid classes responding were phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine, sterols and sterol esters, in a proportion that approximately reflected the increase in plasma vitellogenin (VtG) levels as measured by a non-competitive enzyme-linked immunosorbent assay (ELISA). Plasma non-esterified fatty acids and triacylglycerol were not affected by E 2 treatment. Plasma growth hormone GH levels were increased, and plasma somatostatin-14 (SRIF) levels decreased in E 2 -treated fish, responses which could be secondary to elevated plasma lipid (VtG) content, although a direct E 2 action on somatotroph function is possible. Plasma T 4 concentrations were not affected by E 2 treatment, but plasma T 3 concentrations were significantly lower than in controls 1 week after implantation when plasma E 2 concentrations were the highest; this is in support of the hypothesis that E 2 has a suppressive action on T 3 production. 2001 The Fisheries Society of the British Isles

Effect of diet and ration on the relationship between plasma GH and IGF-1 concentrations in Arctic charr, Salvelinus alpinus (L.)

“…In addition to changes in the somatotropic axis related to diet quantity, lipid‐rich diets have been found to cause an increase in plasma GH concentrations in several fish species (reviewed by Pérez‐Sánchez 2000), including Arctic charr (Cameron et al 2002). The response may be in compensation to elevated plasma lipid concentrations, since a similar elevation of plasma GH concentrations is found in sexually mature salmonid fish in which the plasma levels of the phospholipoprotein, vitellogenin, are elevated (reviewed by Holloway & Leatherland 1998), and plasma GH concentrations are strongly correlated with 17β‐estradiol‐induced increases in plasma polar and neutral lipid concentrations, and with plasma vitellogenin concentrations in rainbow trout (Mercure et al 2001). Conversely, the increase in plasma GH concentrations in fish fed lipid‐rich diets may represent a compensatory response to enhance protein sparing, since although these diets have a high caloric content, they have relatively low protein availability.…”

“…In fish, lipids appear to influence the homeostasis of the somatotropic axis, as high lipid diets initiate an elevation in plasma GH concentrations (Pérez‐Sánchez, Martí‐Palanca & Kaushik 1995; Martí‐Palanca, Martínez‐Barberá, Pendón, Valdivia, Pérez‐Sánchez & Kaushik 1996; Cameron, Gurure, Reddy, Moccia & Leatherland 2002). This increased plasma GH concentration might be a compensatory response to elevated plasma lipid levels, such as those reported for rainbow trout ( Oncorhynchus mykiss , Walbaum) (Mercure, Holloway, Tocher, Sheridan, Van Der Kraak & Leatherland 2001). Equally, the elevated GH levels may be a protein sparing response in fish fed diets with reduced protein availability (Cameron et al 2002).…”

Effects of fasting on temporal changes in plasma concentrations of sex steroids, growth hormone and insulin‐like growth factor I, and reproductive investment in Arctic charr

“…There was no apparent relationship between reproductive development and either GH or IGF‐I in the present study, indicating that neither of these factors are primary links between growth and reproductive development in repeat spawning Arctic charr. This contrasts with studies on other salmonids where elevated plasma GH has been linked to first time maturation (Sumpter et al ., 1991; Le Gac et al ., 1992; Björnsson et al ., 1994; Kakisawa et al ., 1995; Mercure et al ., 2001). Further, Shearer & Swanson (2000) found that maturing 1+ year male chinook salmon Oncorhynchus tshawytscha (Walbaum) grew larger and had elevated plasma IGF‐I in the period December to September compared to non‐maturing fish, although the elevated IGF‐I could not be linked specifically to growth or maturation.…”

“…Several lines of evidence indicate a central role of GH in the reproductive development of fishes. These include observations of elevated plasma GH levels in sexually mature fishes, increased plasma GH levels following administration of sex steroid hormones and the stimulatory effect of GH on the production of gonad steroid hormones (Le Gac et al ., 1993; Holloway & Leatherland, 1998; Holloway et al ., 1999; Mercure et al ., 2001). Recent studies provide evidence that IGF‐I might be a link between somatic development and puberty (Huang et al ., 1998).…”

Multiple molecular effect pathways of an environmental oestrogen in fish

“…Cyr et al 1988, Mercure et al 2001, Qu et al 2001, McCormick et al 2005, although responses were highly variable between studies. In rat, E 2 also decreased serum T 3 (but not T 4 ) levels (probably through an inhibitory effect of E 2 on deiodinase conversion of bioinactive T 4 to bioactive T 3 ), and may influence the hypothalamic/pituitary setpoint for the negative feedback effect of thyroid hormone on thyroid stimulating hormone secretion (Schmutzler et al 2004, Seidlova-Wuttke et al 2005.…”