Effect of insulin/IGF-I like peptides on glucose metabolism in the white shrimp Penaeus vannamei

The insulin-like hormone superfamily encompasses insulin, relaxin, and insulin-like growth factors I (IGF1) and II (IGF2). Insulin hormones regulate cell growth, metabolism, and tissue-specific functions. The presence of insulin has been demonstrated in various invertebrates, and their function as growth promoting or controlling factors has been established in molluscs and insects. In crustaceans, the presence of insulin/insulin-like growth factor (IGF)-like peptides has also been suggested and functional studies have been associated with metabolic control. The general aim of the current study was to elucidate the functional significance of insulin-like peptides in the white shrimp Penaeus vannamei. Because the primary structure of Penaeus insulin is yet unknown, we examined the effect of mammalian insulin/IGF-I on glucose metabolism in P. vannamei. Juvenile shrimps were injected with a single dose of recombinant human (rh) IGF-I or bovine insulin in intermolt stage. Glucose/glycogen levels in shrimp hemolymph and tissues (muscle, hepatopancreas and gills) were determined over a 5 h period by means of an enzymatic analysis. We showed that an injection of rhIGF-I induced a significant (P < 0.01) increase in glucose levels in hemolymph, 1 h after injection and followed by a decrease (P < 0.05) 5 h post-injection. In the hepatopancreas, an increase (P < 0.05) in the glycogen content was observed 3 h after insulin treatment. Finally, a significant elevation (P < 0.01) of glycogen content in the gills throughout the entire sampling period was detected. Our study suggests the presence of endogenous Penaeus insulin(s) that, just like its vertebrate counterparts, is likely to be involved in the regulation of carbohydrate metabolism in crustaceans.