The coelomic red blood cells, or haemocytes, of the sipunculan worm Themiste Dyscrita (Fisher, 1952) were found to contain high concentrations of glycogen: the haemocytes accounted for approximately 56 % of the total glycogen in the organism. Haemocytes, incubated in a glucose-free medium in vitro, released D-glucose into the medium. At 10°C and at a physiological haematocrit, the concentration in the initially glucose-free medium reached physiological plasma levels of D-glucose (0.27 mmoll−1) in about 3h. The cells continued to release D-glucose and the medium concentration reached about 0.65 mmol l−1 after 24 h. Cells resuspended in plasma also released D-glucose to produce medium concentrations that also appeared to exceed physiological levels. Kinetic analysis of membrane transport of D-glucose suggested that membrane transfer was not the rate-limiting step in this release. Mammalian insulin, epinephrine and glucagon were not effective in influencing D-glucose release. No reduction in the medium concentration of D-glucose could be detected when haemocytes were incubated in 2 mmol l−1 D-glucose in plasma or sea water. The results suggest that the haemocyte is involved in the glucose regulation of the organism, although the regulatory mechanism(s) remains to be elucidated. Furthermore, the results suggest that, in addition to its function in oxygen transport, the red blood cell is the principal storage tissue for glycogen in this organism.

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