How Methionine Enkephalin, FK 33-824, and Naloxone Affect Blood Sugar Levels in Freshwater Crabs

Injection of the opioid methionine-enkephalin significantly elevated hemolymph glucose levels in the freshwater crab Oziotelphusa senex senex.

• Opioid agonist and antagonist treatments were applied to investigate their effects on glucose levels.
• Methionine-enkephalin and FK 33-824 injections led to a notable increase in hemolymph glucose.
• Naloxone injections resulted in a decrease in hemolymph glucose levels.
• Naloxone blocked the glucose-increasing effect of methionine-enkephalin when given beforehand.
• No significant changes in glucose levels were observed in eyestalk-less crabs after injecting methionine-enkephalin, FK 33-824, or naloxone.
• The findings suggest that glucose level alterations are likely linked to hormone release stimulated by methionine-enkephalin and FK 33-824 and inhibited by naloxone.

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