Glycemic and insulin responses in white sea bream Diplodus sargus, after intraperitoneal administration of glucose

Abstract

A glucose tolerance test was performed in white sea bream Diplodus sargus, juveniles to evaluate the effect of a glucose load on plasma glucose, insulin, triacylglyceride levels, and on liver glycogen storage in order to study the capability of glucose utilization by this species. 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 rose from a basal level of 4 to a peak of 18-19 mmol l(-1), 2-4 h after glucose injection and fish exhibited hyperglycemia for 9 h. An insulin peak (from 0.5 to 0.8 ng ml(-1)) was observed 2-6 h after glucose injection, and basal value was attained within 9 h. Liver glycogen peaked 6-12 h after the glucose load and thereafter decreased to the basal value which was attained 24 h after injection. Plasma triacylglycerides in glucose-injected fish were only significantly higher than the basal value 12 h after injection. Glucose-injected fish generally showed lower plasma triacylglyceride levels than control fish. Our results indicate that under these experimental conditions, glucose acts as an insulin secretagogue in white sea bream juveniles. Moreover, insulin may have contributed to restoring basal plasma glucose levels by enhancing glucose uptake in the liver. Further studies are needed to corroborate the lipolytic action of glucose. Clearance of glucose from the blood stream was fast, comparatively to other species, indicating that white sea bream has a good capability of glucose utilization.

Selected plasma biochemistry parameters in gilthead seabream (Sparus aurata) juveniles

“…Plasma glucose values determined in this study 24 h after the last meal were consistent with previously reported values for this species (Peres et al., ; Peres and Oliva‐Teles, ; Sitja‐Bobadilla et al., ; Enes et al., ,b), confirming that seabream is able to restore basal glucose levels relatively quickly after feeding. Accordingly, it was previously observed in glucose tolerance tests that basal glucose values were reached within 12 h after a peritoneal injection of 1 g glucose per kg body weight (Peres and Oliva‐Teles, ; Enes et al., ,b). During starvation, it is presumed that plasma glucose fluctuates mainly due to increase of liver glycogenolysis and gluconeogenesis (Navarro and Gutierrez, ; Enes et al., ,b).…”

“…Accordingly, it was previously observed in glucose tolerance tests that basal glucose values were reached within 12 h after a peritoneal injection of 1 g glucose per kg body weight (Peres and Oliva‐Teles, ; Enes et al., ,b). During starvation, it is presumed that plasma glucose fluctuates mainly due to increase of liver glycogenolysis and gluconeogenesis (Navarro and Gutierrez, ; Enes et al., ,b). Concordantly, an increase of glycogenolytic and gluconeogenic potential of seabream liver was observed after 14 days of fasting, supporting an enhancement in the liver capacity to export glucose (Sangiao‐Alvarellos et al., ).…”

Carbohydrate tolerance in the fruit-eating fish Piaractus mesopotamicus (Holmberg, 1887)

“…Pacu mobilized glucose faster than the Senegalese sole (10 hr after glucose load) (Conde‐Sieira, Soengas & Valente, ) challenged with the same glucose dose and route of administration and also faster than in studies which used 1 g of glucose/kg BW, such as in the omnivorous white sea bream ( Diplodus sargus L.) (9 hr after glucose load) (Enes et al., ), in the herbivorous blunt snout bream ( Megalobrama amblycephala Yih) (8 hr) (Xu et al., ) and in the carnivorous yellowtail kingfish (12 hr) (Booth et al., ). However, considering that the hyperglycaemic period can be dose‐dependent, as observed in white sturgeon (Gisbert, Sainz & Hung ) and blunt snout bream (Xu et al., ), the results observed in pacu after IP glucose injection need to be carefully interpreted.…”

“…Glucose tolerance tests are practical and widely used to evaluate the ability of fish to utilize carbohydrates, indicating the potential use of high glucose loads (Enes et al., ). The ability of some fish species to incorporate dietary carbohydrate is variable, and in many instances, prolonged postprandial hyperglycaemia is observed (Legate, Bonen & Moon, ; Hemre et al., ).…”

A negative feedback mechanism in the insulin-regulated glucose homeostasis in Japanese flounderParalichthys olivaceusby two ways of glucose administration

“…This was similar with the previous study on Australian snapper Pagrus auratus , in which the blood glucose reached to the peak at 3h (18.9mM) and the hyperglycemia lasted for about 18 hours (Booth, Anderson et al 2006). However, after intraperitoneal injected same or even a higher dose of glucose, some omnivorous fish like tilapia, white sea bream, spends from 1-2 hours reaching to the peak in the concentration of blood glucose and 6-9 hours recovering as usual (Wright Jr, O’Hali et al 1998, Enes, Peres et al 2012). It was suggested that the omnivorous fish species had higher ability of blood glucose control than the carnivorous.…”