Liver insulin-like growth factor-I mRNA is not affected by diet composition or ration size but shows diurnal variations in regularly-fed gilthead sea bream (Sparus aurata)

Nutritional regulation of insulin-like growth factor-I (IGF-I) mRNA was assessed in liver of gilthead sea bream (Sparus aurata). As in mammals, starvation lowered the IGF-I mRNA content, which was recovered by refeeding. However, in contrast to previous observations in rats, neither diet composition nor ration size significantly affected hepatic IGF-I mRNA. Although fish growth depended on the quantity of diet supplied, no relationship was found between growth and liver IGF-I mRNA levels, a fact that challenges the importance, at least in fish, of liver-derived IGF-I on body growth attributed by the classical somatomedin hypothesis. In addition, diurnal modulation of mRNA levels occurred following food intake, suggesting that the intake of food may play a key role in the regulation of the short-term anabolic effects of IGF-I.