Methionine-enkephalin induces hyperglycemia through eyestalk hormones in the estuarine crab Scylla serrata

The hypothesis is tested that methionine-enkephalin, a hormone produced in and released from eyestalk of crustaceans, produces hyperglycemia indirectl y by stimulating the release of hyperglycemic hormone from the eyestalks. I njection of methionine-enkephalin leads to hyperglycemia and hyperglucosemi a in the estuarine crab Scylla serrata in a dose-dependent manner. Decrease s in total carbohydrate (TCHO) and glycogen levels of hepatopancreas and mu scle with an increase in phosphorylase activity were also observed in intac t crabs after methionine-enkephalin injection. Eyestalk ablation depressed hemolymph glucose (19%) and TCHO levels (22%), with an elevation of levels of TCHO and glycogen of hepatopancreas and muscle. Tissue phosphorylase act ivity decreased significantly during bilateral eyestalk ablation. Administr ation of methionine-enkephalin into eyestalkless crabs caused no significan t alterations in these parameters when compared to eyestalk ablated crabs. These results support the hypothesis that methionine-enkephalin produces hy perglycemia in crustaceans by triggering release of hyperglycemic hormone f rom the eyestalks.