Effects of somatostatin on the growth hormone-insulin-like growth factor axis and seawater adaptation of rainbow trout (Oncorhynchus mykiss)

Growth hormone (GH) has been shown to contribute to the seawater (SW) adaptability of euryhaline fish both directly and indirectly through insulin-like growth factor-1 (IGF-1). This study examined the role of somatostatin-14 (SS-14), a potent inhibitor of GH, on the GH–IGF-1 axis and seawater adaptation. Juvenile rainbow trout (Oncorhynchus mykiss) were injected intraperitoneally with SS-14 or saline and transferred to 20 ppt seawater. A slight elevation in plasma chloride levels was accompanied by significantly reduced gill Na+, K+-ATPase activity in SS-14-treated fish compared to control fish 12 h after SW transfer. Seawater increased hepatic mRNA levels of GH receptor 1 (GHR 1; 239%), GHR 2 (48%), and IGF-1 (103%) in control fish 12 h after transfer. Levels of GHR 1 (155%), GHR 2 (121%), IGF-1 (200%), IGF-1 receptor A (IGFR1A; 62%), and IGFR1B (157%) increased in the gills of control fish 12 h after transfer. SS-14 abolished or attenuated SW-induced changes in the expression of GHR, IGF-1, and IGFR mRNAs in liver and gill. These results indicate that SS-14 reduces seawater adaptability by inhibiting the GH–IGF-1 axis.