Anaerobic Excretion of Fermentation Acids by Hymenolepis diminuta during Development in the Definitive Host

Abstract

Succinic, acetic, and lactic acids are the major anaerobic fermentation acids excreted in vitro by Hymenolepis diminuta. In parasites recovered from immature (6-day) infections in white rats that were fed ad lib. in the dark for 12 hr, approximately equal amounts of succinic and lactic acids, and less acetic acid, were excreted. In the succeeding 12-hr period of fasting in the light, production of succinic and acetic acids from endogenous glycogen reserves was unaffected, whereas that of lactic acid decreased markedly. The pattern was different in parasites recovered from 10and 14-day infections, in that quantitative differences in acid excretion during feeding and fasting periods were not observed, lactic acid production was relatively small, and succinic acid constituted about half of the total excreted acids. An active pyruvate decarboxylase enzyme complex presumably accounted for the formation of acetate from pyruvate. The existence of lactate dehydrogenase, and a phosphoenolpyruvate carboxykinase leading to succinate production were already known. A calculation of the carbon content of excreted acids in terms of ,moles phosphoenolpyruvate carbon/mg protein showed that the rates of excretion of fermentation acids in 6and 14-day infections did not differ. Succinic, acetic, and lactic acids comprise most of the total fermentation acids excreted in vitro by Hymenolepis diminuta recovered from patent (15 day) infections in rats (Fairbairn et al., 1961). It is known that phosphoenolpyruvate is a key intermediate in the formation of these acids since it reacts with carbon dioxide in the presence of phosphoenolpyruvate carboxykinase and GDP or IDP to form oxaloacetate and thence succinic acid, and is also converted to pyruvate by pyruvate kinase (Bueding and Saz, 1968) and hence to L(+) lactate by lactate dehydrogenase (Walkey and Fairbairn, 1973). Acetic acid is presumably formed by oxidative decarboxylation of pyruvate, although the existence of this enzyme complex has not been studied. Different isoenzymes of L(+) -lactate dehydrogenase occur in the anterior regions of the mature tapeworm strobila or in immature (6 day) parasites, and in infective eggs obtained from mature proglottids (Walkey and Fairbairn, 1973). Similar observations have been made on pyruvate kinase (Carter and Fairbairn, unpublished). There is reason to believe, therefore, that quantitative differences in the forReceived for publication 11 February 1974. * This work was supported by Grants AI-08491 and 5 TOI AI-226 from the NIH, Bethesda, Maryland 20014. t Present address: The Wellcome Research Laboratories, Beckenham, Kent BR3 3BS, England. mation and excretion of succinic, acetic, and lactic acids may exist in different regions of the strobila, or in parasites at different stages of development in the definitve host. This is not surprising, as the strobila of H. diminuta contains hundreds of proglottids representing all stages of continuous growth and differentiation. In the present investigation we have compared the in vitro anaerobic excretion of succinic, acetic, and lactic acids by H. diminuta recovered from infected rats after 6 and 14 days, respectively, and have demonstrated the decarboxylation of pyruvate by a pyruvate decarboxylase enzyme complex. MATERIALS AND METHODS In order to make possible a comparison of the present experiments with other recently completed experiments (Carter and Fairbairn, unpublished), white, male Sprague-Dawley rats (Holtzman strain) weighing about 150 g each were infected with 30 cysticercoids of H. diminuta injected into the stomach through a catheter. After ensuring that all cysticercoids had been delivered from the catheter, the rats were caged in pairs and maintained on a 12 hr light-12 hr dark daily photoperiod. Food (commercial pellets) was provided only during the dark half of the cycle, from 8:00 PM to 8:00 AM. Rats harboring parasites to be recovered on the 10th or 14th day after infection were maintained in this manner. When parasites were to be recovered after infection for 6 days the procedure was the same except that greater numbers of rats were infected, each with 300 to 500 cysticercoids, in order that sufficient weight of tissue would be available for