A cross-talk between leptin and 17β-estradiol in vitellogenin synthesis in rainbow trout Oncorhynchus mykiss liver.

The existence of nutritional and energy reserves is fundamental for fish female fertility, so that the existence of a correlation between metabolic reserves and reproductive capacity is suggested. Leptin regulates body weight and energy homeostasis. Estradiol induces the synthesis of vitellogenin, a phospholipoglycoprotein produced by the liver and taken up by the growing oocytes. The objective of this study was to investigate the possible existence of a crosstalk between 17β-estradiol (E) and leptin in the modulation of E-induced vtg in the rainbow trout Oncorhynchus mykiss. Liver slices were incubated with recombinant trout leptin (rt-lep) at three different concentrations (1-10-100 ng/ml). rt-lep brought about the decrease of E-induced vtg secretion in the medium and the down-regulation of vtg mRNA expression. Moreover, rt-lep stimulated the lipase activity and diminished the liver fatty acid content. The combined employment of signal transduction inhibitors and the analysis of signal transduction phosphorylated factors revealed that rt-lep effect on E-induced vtg occurred through the activation of phosphodiesterase, protein kinase C, MAP kinases, and protein kinase A. In conclusion, our study suggests that leptin influences E-induced vtg synthesis in the rainbow trout Oncorhynchus mykiss by modifying both the protein and the lipid components.