Insulin and IGF-I response to a glucose load in European sea bass (Dicentrarchus labrax) juveniles

A glucose tolerance test was performed in European sea bass juveniles to evaluate the effect of a glucose load on plasma insulin and insulin-like growth factor-I (IGF-I) levels. Interaction between these hormones, plasma triacylglycerides and liver glycogen was also determined. After being fasted for 48 h, fish were intraperitoneally injected with either 1 g of glucose per kg body weight or a saline solution. Plasma glucose levels peaked at 23-25 mmol l(-1), 2-6 h after the glucose injection and fish exhibited hyperglycemia until 12 h, when plasma glucose recovered to basal levels. Plasma insulin levels did not change significantly between sampling points, but insulin level was higher in the glucose group than in the control 4-6 h and 24 h after injection. Though plasma IGF-I levels remained constant for a long time (except at time 12 h) in the glucose injected fish, at times 6-9 h, 24 h and 48 h IGF-I levels were higher in the glucose group than in the control. Glucose administration led to lower plasma triacylglyceride levels than saline solution at times 9-12 h. Although liver glycogen content was not affected by the glucose injection (except at times 4 h and 48 h), comparative to saline solution injection, there was a significant increase of liver glycogen at 6 h and 9 h. Results of this study indicate that under these experimental conditions glucose is probably not the most important stimulator of insulin release. Insulin may have contributed to the increase of IGF-I levels and to the enhancement of glucose uptake by the liver in glucose injected fish. (C) 2011 Elsevier B.V. All rights reserved.