The Hyperglycemic Effect of Melatonin in the Chinese Mitten Crab, Eriocheir sinensis

Abstract

Melatonin has been identified in a variety of invertebrate species, but its function is not as well understood as in crustaceans. The effects of melatonin on hemolymph glucose levels and tissue carbohydrate metabolism in the Chinese mitten crab, Eriocheir sinensis, were fully investigated in this study. Moreover, whether the eyestalk (an important endocrine center in invertebrate species) involves in this process or not, also were clarified. Analysis revealed that eyestalk ablation, especially bilateral, caused a significant decrease in the hemolymph glucose level. Moreover, injection of melatonin induced hyperglycemia in a dose-dependent manner both in intact and ablated crabs. Based on the expression of CHH mRNA in the 10 different tissues, eyestalk, thoracic ganglion, intestinal tract and hemolymph were selected to estimate the effect of melatonin on the expression of CHH mRNA. Bilateral eyestalk ablation caused a significant increase in the expression of CHH mRNA in the thoracic ganglion, intestinal tract and hemolymph compared with the controls. In addition, injection of melatonin into intact or ablated crabs elevated the CHH mRNA level in the eyestalk, thoracic ganglion and intestinal tract tissues compared with controls. The hemolymph CHH mRNA after melatonin injection was elevated only in ablated crabs. Administration of melatonin resulted in a significant decrease in total carbohydrates and glycogen levels with an increase in phosphorylase activity levels in the hepatopancreas and muscle in intact and ablated crabs. Our findings demonstrated that melatonin can induce hyperglycemic effects in both intact and ablated crabs, suggesting that this effect is probably not mediated solely via eyestalk.

Keywords: Eriocheir sinensis; crustacean hyperglycemic hormone; eyestalk; glucose; melatonin.

Figure 1

The hemolymph glucose level of E. sinensis in intact (C), unilateral (Unil-ablated) and bilateral eyestalk ablated (Bil-ablated) crabs (n = 10). Each bar represents a mean ± SE of 10 individual crabs. Values in a row with different lowercase letters denote significant differences (p < 0.05).

Figure 2

Dose-dependent effects of melatonin on hemolymph glucose level in both intact and ablated crabs, E. sinensis. The results are shown as the means ± SE (n = 10). The different capital letters in the open bars indicate a significant difference between intact crabs (p < 0.05); the different lowercase letters in the solid bars indicate significant differences between ablated crabs (p < 0.05). Asterisk (^*) represents a significant difference (p < 0.05) between the intact and ablated groups.

Figure 3

Time course of melatonin-induced hyperglycemia in intact crabs, E. sinensis. The results are shown as the means ± SE (n = 10). The different lowercase letters indicate significant differences between the groups (p < 0.05).

Figure 4

Effect of the injection of melatonin into intact crabs on expression of CHH mRNA in tissues. The results are represented as the means ± SE (n = 10). Values above a bar with different lowercase letters denote significant differences between the groups (p < 0.05). Eye, eyestalk; Tho, thoracic ganglion; Cer, cerebral ganglion; Int, intestinal tract; Hep, hepatopancreas; Sto, stomach; Hea, heart; Hem, hemolymph; Mus, muscle; Gil, gill.

Figure 5

Comparisons of CHH mRNA expressions in the eyestalk (A), thoracic ganglion (B), intestinal tract (C) and hemolymph (D) in intact and, ablated crabs (E. sinensis), both injected with melatonin (C+MT and Ablated+MT). Results are shown as the means ± SE (n = 10). Asterisk (^*) represent significant differences between the C and C+MT, C and Ablated, Ablated and Ablated+MT groups.