On the isolation and characterisation of a crustacean hyperglycaemic hormone in the eyestalk of the shrimp Penaeus indicus

Abstract

In decapod crustaceans, the eyestalk represents the pivotal source for several neuropeptides influencing various physiological activities concerned with metabolism, growth and reproduction. Prominent among them is the crustacean hyperglycaemic hormone (CHH) which regulates the blood glucose level by its `diabetogenic' action. This paper reports on the first characterisation of a CHH in the commercially important penaeid species Penaeus indicus. Reversed phase HPLC of extracts from eyestalk ganglia on a Waters μ-Bondapak phenyl column combined with an enzyme linked immunosorbent assay revealed that among six immunoreactive peptide fractions in total a late eluting peak fraction with the retention time of about 50 min shows the strongest immunoreactivity to a polyclonal rabbit antiserum raised against the CHH of the freshwater crayfish Orconectes limosus. The amino acid composition of this peptide, purified by rechromatography was determined according to the orthophthaldialdehyde post column derivatisation method. The most interesting features are the low molar concentration of acidic amino acid residues (e.g. Asx, Glx) but a high molar concentration of lysine residues. The CHH material was localised immunocytochemically in the neurosecretory centres of X-organ sinus gland system using the same antiserum. A large number of perikarya of the medulla terminalis X-organ, the neural tract as well as the sinus gland showed intense immunoreactivity. Though the hyperglycaemic response of this HPLC purified CHH of P. indicus was found to be very poor when injected into eyestalkless as well as eyestalk-intact crayfish, O. limosus, it clearly induced hyperglycaemia in P. indicus.