Regulation of growth hormone and insulin-like growth factor-1 secretion in response to key amino acids in gilthead sea bream.

Abstract

In vertebrates, growth hormone (GH) and insulin-like growth factors (IGFs) are key regulators of somatic growth. In fish, Gh and Igf1 secretion is strongly influenced by nutritional status, with dietary protein levels and, particularly, amino acids (AA) composition, being the major determinants of hormonal modulation. This study investigated the regulation of the Gh/Igf axis by selected AA in gilthead sea bream (Sparus aurata) using complementary experimental approaches. Intraperitoneal injection of individual AA elicited distinct endocrine responses, with lysine (Lys) being the most potent stimulator of Gh secretion, followed by arginine (Arg), whereas methionine (Met) had no significant effect. In contrast, administration of all tested AA, including Met, as well as human GH, significantly increased plasma Igf1 levels. Ex vivo, rainbow trout Ghrelin stimulated and human IGF1 inhibited Gh release from hemi pituitaries, validating the experimental system. Among the AA tested, Arg and leucine (Leu) did not affect hemi pituitaries Gh secretion, whereas Lys strongly stimulated it. Isolated hepatocytes gene expression analyses revealed that Arg and Met significantly increased total igf1 mRNA levels after 24 h of incubation, while Leu and Lys had no effect. Conversely, Leu markedly upregulated igf2 expression at 6 h. Stimulatory effects on igf1 splice variants and related genes were mainly observed after 6 h. Overall, these results provide an integrative view of AA-dependent regulation of the Gh/Igf axis in gilthead sea bream with tissuespecific responses, highlighting the differential stimulatory effects of Lys, Arg and Met and supporting targeted AA supplementation strategies for improving aquaculture production.