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The role of eyestalk factors in carbohydrate regulation in the crab Cancer magister Skelton, Holly Louise

Abstract

Crustacean hyperglycemic hormone (CHH), located in the sinus gland of the decapod crustacean eyestalk, is proposed to be the primary carbohydrate regulatory hormone in these animals. However, its physiological role is poorly characterized. In this study, the role of eyestalk factors in regulating carbohydrates under control and severely hypoxic (emersion) conditions was investigated in the crab Cancer magister. Previously, dramatic increases in hemolymph flow to the sinus gland, via the anterior aorta, had been proposed to be essential for increases in circulating concentrations of CHH observed during emersion stress. Therefore, ligation of this artery was hypothesized to be an effective means of manipulating circulating hormone titers. The data presented here indicates that, under control conditions, eyestalk extracts (ESE) from C. magister contain an active factor(s) which, when injected into whole animals, cause hyperglycemia in a dose dependent manner. Eliminating flow through the anterior aorta does not annul ESE injection induced hyperglycemia. Carbohydrate stores in heart, hepatopancreas and muscle tissue were affected by anterior aorta ligation and, may therefore be target tissues. Injection of eyestalk extract had no effect on heart, gill, hepatopancreas or muscle carbohydrate content. Treatment of isolated muscle tissue with eyestalk extract had no effect on glucose release and, therefore, did not support the proposed mode of action of CHH. Under emersion stress conditions, hyperglycemia occurs but is prevented if eyestalk factors cannot circulate (anterior aorta ligated animals). Changes in glycogen content of muscle and hepatopancreas identified these tissues as potential targets of eyestalk factor(s) during emersion. Again, in vitro studies of isolated muscle tissue did not support the proposed mode of action of CHH. Finally, the presence of CHH like peptides in eyestalk extracts prepared from C. magister tissue was demonstrated and provides support for the hypothesis that this hormone is responsible for the results observed. The results are discussed in relation to hormonal involvement in metabolic depression displayed by emersed aquatic decapod crustaceans.

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