Regulation of the somatotropic axis by dietary factors in rainbow trout (Oncorhynchus mykiss).
The activity of the somatotropic axis was analysed in juvenile rainbow trout (Oncorhynchus mykiss) fed either a fishmeal-based diet (FM) or graded levels of plant proteins to replace 50% (PP50 diet), 75% (PP75 diet) or 100% (PP100 diet) of the fishmeal protein. For this purpose, partial cloning and sequencing of the gene encoding rainbow trout growth hormone receptor (GHR) was first accomplished by RT-PCR, using degenerate primers based on the sequences of non-salmonid fish GHR. Growth rates and energy retention were lowered by the PP75 and PP100 diets and a concurrent and progressive increase in plasma levels of growth hormone (GH) was found. However, no changes in hepatic GH binding and total plasma insulin-like growth factor (IGF)-I levels were observed among the four experimental groups. This fact agrees with the lack of changes in hepatic measurements of GHR and IGF-I transcripts. No consistent changes in IGF transcripts were found in peri-visceral adipose tissue and skeletal muscle, but GHR mRNA was up-regulated in the peri-visceral adipose tissue of fish fed the PP75 and PP100 diets, which would favour the lipolytic action of GH. Two specific bands (47 and 33 kDa) of IGF-binding proteins were found in the plasma of all analysed fish, but the sum of the two integrated areas increased progressively with plant protein supply, which might reflect a reduced free IGF availability. Therefore, in our experimental model, the growth impairment could be due, at least in part, to a lowered availability of biologically active IGF (free IGF fraction) rather than to liver GH desensitization or defect in IGF synthesis and release at the systemic and/or paracrine-autocrine level.
Gómez-Requeni
Pedro
P
Instituto de Acuicultura de Torre de la Sal (CSIC), 12 595 Ribera de Cabanes, Castellón, Spain.
Calduch-Giner
Josep
J
Vega-Rubín de Celis
Silvia
S
Médale
Françoise
F
Kaushik
Sadasivam J
SJ
Pérez-Sánchez
Jaume
J
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001682:Biological Availability; D015152:Blotting, Northern / Q000379:methods; D004044:Dietary Proteins / Q000008:administration & dosage*; D005396:Fish Products; D013006:Growth Hormone / Q000097:blood / Q000378:metabolism*; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D017686:Oncorhynchus mykiss / Q000254:growth & development / Q000378:metabolism*; D010940:Plant Proteins / Q000008:administration & dosage*; D011485:Protein Binding; D012333:RNA, Messenger / Q000032:analysis; D011986:Receptors, Somatotropin / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D004044:Dietary Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D010940:Plant Proteins; D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone