Aspects carbohydrate metabolism in the plerocercoid of Schistocephalus solidus.

Abstract

Three spined sticklebacks infected with Schistocephalus solidus plerocercoids were used for in-vivo experiments to determine the relative distribution of 14C-labelled sugars (D-glucose and 3-0-M D-glucose) in fish and worm tissues. A maximum of 23.6% labelled material from D-glucose was found in plerocercoids after 4.5 hours and a maximum of 2.8% labelled material from 3-0-M glucose after 24 hours. Comparison of distribution levels between the two sugars and between infected and uninfected fish tissues did not show significant differences except in a few cases. In-vitro studies with plerocercoids demonstrate D-glucose uptake to be sodium dependent, saturable with an apparent Kt of O.66mM, inversely related to dry weight and absorbed against a concentration gradient. Uptake is also affected by temperature with high rates at 200 and 400C and lower rates at 100 and 30°C. Uptake is inhibited (non-competitively) by phlorizin and to a lesser extent by ouabain and DNP. The nature of inhibition caused by the latter two compounds was not determined. THe effect of 3-O-M glucose on D-glucose uptake was inconclusive. Similarly the effect of D-galactose was inconclusive and also inconsistent,causing both stimulation and inhibition of D-glucose uptake. A gradient of glucose absorption is present along the length of the plerocercoid; the lowest rate being found at the anterior section and the highest at the posterior end. Plerocercoids incubated under aerobic conditions in 14C-D-glucose produced insignificant amounts of labelled CO2. Under aerobic conditions lactate is produced by plerocercoids at the rate of O.13mg/ml/hour but no detectable amounts of pyruvate were found under similar conditions. Glycogen extracts from plerocercoids incubated in-vivo contain increasing levels of 14C-labelled material with increased incubation periods. Host metabolism is significantly affected by the presence of plerocercoids. Lower levels of glycogen are found in the liver tissue of infected fish compared to uninfected fish. Also the rate of D-glucose uptake by fish stomach and intestinal tissues is considerably reduced in infected fish.