Mode of Action of Retinoic Acid in the Regulation of Glucose Metabolism in Mud Crab, Scylla serrata: Evidence for the Involvement of Crustacean Hyperglycemic Hormone

In the current study, we evaluated the effect of retinoids, 9-Cis retinoic acid (9CRA) and all-trans retinoic acid (ATRA) on carbohydrate metabolism in the mud crab, Scylla serrata. Intact and eyestalk ablated male crabs (n=10 crabs per group) were selected and retinoic acid isomers, 9CRA and ATRA were injected into the crabs. Parallel controls were maintained. Significant reduction in the hemolymph sugar levels was observed in crabs subjected to eyestalk ablation (ESX) over intact crabs. Injection of 9CRA into intact but not in ESX crabs exhibited a dose- and time-dependent manner hyperglycemic response. ATRA administration did not induce hyperglycemia either in intact or ESX crabs. Injection of 9CRA showed a significant decrease in total carbohydrate content and glycogen levels in hepatopancreas and muscle tissues of intact crabs over their respective controls. Further, the activity levels of glycogen phosphorylase were also elevated in selected tissues of intact crabs administered with 9CRA. In addition, intact crabs which received 9CRA resulted in up regulation of expression of CHH mRNA from the eyestalks. Taken together, we postulate that 9CRA-induced hyperglycemia might be ascribed to neurotransmitter effects mediating the release of CHH from the eyestalk. The release of CHH eventually caused glycogenolysis in the selected hepatopancreas and muscle tissues of the mud crab Scylla serrata thereby hyperglycemia.