Effects of Adrenosterone, Testosterone, and 17 β ‐Estradiol on the Gene Expression of Insulin‐Like Growth‐Factor Binding Proteins ( igfbps ) in Atlantic Salmon Smolts

The growth hormone (Gh)/insulin-like growth-factor (Igf) system is a key regulator of growth in teleost fishes, including salmonids. Igfs interact with a suite of binding proteins, termed Igf binding proteins (Igfbps), which modify their biological activities. Atlantic salmon (Salmo salar) express an expanded array of igfbp gene transcripts in liver, the primary site of Igfbp production. While gonadal steroids are known to impact the growth of fishes, there is little information on how androgens and estrogens affect the expression of various igfbps. In the current study, we characterized how 14-day implants of adrenosterone (OA), testosterone (T) or 17β-estradiol (E2) affected the Gh/Igf/Igfbp network in Atlantic salmon smolts. OA did not affect any of the parameters studied. There were no effects of T or E2 on body mass, plasma levels of Igf1, or hepatic igf1, igf2 or gh receptor mRNA levels. E2 stimulated hepatic estrogen receptor α mRNA levels by 17-fold, while E2 and T stimulated hepatic vitellogenin ...