Effects of dietary genistein on GH/IGF-I axis of Nile tilapia Oreochromis niloticus

There is considerable concern that isoflavones, such as genistein in fish feed composed of soybean protein, affects somatic growth in fish. Our previous works demonstrated that 30 and 300 mu g/g dietary genistein had no significant effect on growth performance in Nile tilapia (Oreochromis niloticus), but the higher level of genistein (3 000 mu g/g) significantly depressed growth. This study was conducted to further examine the effects of dietary genistein on the endocrine disruption on growth hormone/insulin-like growth factor-I (GH/IGF-I) axis in Nile tilapia (O. niloticus). Juvenile fish were fed by hand twice daily to satiation with one of four isonitrogenous and isoenergetic diets, each containing either 0, 30, 300 or 3 000 mu g/g genistein. Following an 8-week feeding period, plasma GH and IGF-I levels were investigated by radioimmunoassay and gene expression levels of gh, ghrelin, gnrhs, ghr, npy, npyrs, pacap, ghrs, igf-I, igf-Ir, and igfbp3 were examined by real-time PCR. The results show that no significant change in plasma GH and IGF-I levels in fish fed with diets containing 30 mu g/g and 300 mu g/g genistein. mRNA expression of genes along the GH/IGF-I axis remained unaffected, except for igf-Ir, which was stimulated by the 300 mu g/g genistein diet. While in fish fed the 3 000 mu g/g genistein diet, the plasma GH and IGF-I levels decreased, and mRNA expression of gh, ghr2, npyr1, igf-I, and igf-Ir were also significantly depressed. In contrast, npy and igfbp3 mRNA expression were enhanced. This study provides convincing evidence for growth impediment by genistein by disturbing the GH/IGF-I axis in Nile tilapia O. niloticus