Insulin and IGF-I receptors in trout adipose tissue are physiologically regulated by circulating hormone levels.
In fish, insulin is believed to act on adipose tissue to promote lipid accumulation, but a direct role for insulin in fish adipose tissue lipogenesis has yet to be demonstrated. To investigate the role of insulin and insulin-like growth factor I (IGF-I) in fish adipose tissue function, we have investigated the presence and the regulation of insulin and IGF-I receptors in adipose tissue of brown trout (Salmo trutta). Receptors for insulin and IGF-I were detected in trout adipose tissue, with IGF-I receptors being more abundant (two- to tenfold) and having a higher affinity (twofold) than insulin receptors. In contrast to the situation in mammals, arginine treatment, which elevates the levels of insulin and IGF-I in plasma, increased the number of insulin receptors 1.7-fold and the number of IGF-I receptors 2.3-fold. When plasma levels of insulin and IGF-I were decreased by fasting, insulin receptor numbers fell 3.6-fold and IGF-I receptor numbers fell 2.2-fold. These results demonstrate for the first time the presence of specific insulin and IGF-I receptors in adipose tissue of ectothermic vertebrates and suggest that adipose tissue may be a target for the actions of insulin and IGF-I in fish.
Planas
J V
JV
Departament de Fisiologia, Facultat de Biologia, Universitat de Barcelona, Avinguda Diagonal 645, E-08071 Barcelona, Spain. planas@porthos.bio.ub.es.
Méndez
E
E
Baños
N
N
Capilla
E
E
Navarro
I
I
Gutiérrez
J
J
D000273:Adipose Tissue / Q000502:physiology*; D000818:Animals; D007328:Insulin / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D017526:Receptor, IGF Type 1 / Q000502:physiology*; D014337:Trout / Q000502:physiology*
D007328:Insulin; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1