Studies on the physiology of a shrimp, Metapenaeus sp. (Crustacea: Decapoda: Penaeidae). IV. Carbohydrate metabolism

Abstract

By use of a closed recirculating system for carbon dioxide collection, it was found that the greater part of [¹⁴C]glucose, either fed or injected, appeared as ¹⁴CO₂ within 24 hr. Up to 2% was incorporated as polysaccharide. Extract of sensory-pore-complex did not affect ¹⁴C distribution but eyestalk ablation reduced ¹⁴C₂, output to about two-thirds, with a corresponding increase in body carbohydrate ¹⁴C. A small amount of the ¹⁴C was incorporated in both carbonate and non-carbonate fractions of the cuticle. Eyestalk ablation caused a highly significant reduction in blood reducing substances, while sensory-pore extract caused a significant increase.

Blood of intermoult animals contained 39.2-42.0 µg/ml glucosamine in plasma proteins, and 3.3-4.0 µg/ml in cells, but in premoult animals plasma content fell to 10 µg/ml and cells increased to 72.3 µg/ml. Eyestalk ablation reduced plasma glucosamine only, while sensory-pore-complex extract raised total blood glucosamine slightly. Glucosarnine of the epidermis increased 10-fold following eyestalk ablation. On the assumption that hexosamine comprises about one-third of the total sugars in mucopolysaccharides, mucopolysaccharide : glycogen ratios were calculated as 1 : 1 for epidermis, but were 5.3 : 1 for digestive gland, due to epithelial mucins involved in digestion.

Oxidation of [¹⁴C] glucose in Metapenaeus, Metapograpsus, and Hemigrapsus are compared, and it is suggested that glycogen does not play a major role in Metapenaeus, the animal being deaendent on a sustained intake of food for both oxidative metabolism and chitin synthesis. "Moult-accelerating hormone" of the sensory-pore-complex may be a hyperglycaemic hormone responsible for mobilization of body carbohydrates. It is suggested that an acid mucopolysaccharide is supplied by the blood to the epidermis as a chitin precursor, the source being blood amoebocytes.