Putative involvement of crustacean hyperglycemic hormone isoforms in the neuroendocrine mediation of osmoregulation in the crayfishAstacus leptodactylus

Abstract

SUMMARYThis study investigates the involvement of eyestalk neuroendocrine factors on osmoregulation in the crayfish Astacus leptodactylus maintained in freshwater. Eyestalk removal was followed by a significant decrease in hemolymph osmolality and Na+ concentration and by a 50% increase in mass after one molting cycle. Several neurohormones have been isolated from the sinus gland through high-performance liquid chromatography (HPLC), and different crustacean hyperglycemic hormone (CHH)-related peptides, including stereoisomers (L-CHH and D-Phe3 CHH), have been identified by direct enzyme-linked immunosorbent assay (ELISA). A glucose quantification bioassay demonstrated a strong hyperglycemic activity following injection of the immunoreactive chromatographic fractions and showed that the D-Phe3 CHH was the most efficient. Destalked crayfish were then injected with purified CHH HPLC fractions. The D-Phe3 CHH fraction significantly increased the hemolymph osmolality and Na+ content 24 h after injection. Two other CHH-related peptides caused a smaller increase in Na+ concentration. No significant variation was observed in hemolymph Cl- concentration following injection of any of the CHH isoforms. These results constitute the first observation of the effects of a CHH isoform, specifically the D-Phe3 CHH, on osmoregulatory parameters in a freshwater crustacean. The effects of eyestalk ablation and CHH injection on osmoregulation and the identification of different CHH-related peptides and isoforms in crustaceans are discussed.