The effects of changes in the definitive host environment on the metabolism of Hymenolepis diminuta during growth and maturation.

Flexibility in the metabolism of Hymenolepis diminuta is associated with changing intrinsic requirements during maturation but is also influenced by extrinsic factors, that is, by the nature of the host environment. End-products of carbohydrate metabolism and enzyme activities in worm extracts were used as indicators of metabolic regulation in H. diminuta recovered at various times postinfection. The predominant end-product from 6-day-old worms is lactate, generated by cytosolic glycolysis. As the cestode matures in the host, lactate production by the whole worm decreases and greater amounts of the mitochondrial end-products, succinate and acetate, are detected. A stable, dichotomous carbon flow to lactate, succinate and acetate is observed from 12 days post-infection. A metabolic gradient along the length of individual strobila is also evident. It extends from glycolysis, in the anterior region, to mitochondrial dismutation in the posterior region. The transition from cytosolic to mitochondrial pathways during maturation and along the strobilus is delayed or suppressed in worms recovered from immunosensitized hosts. Four host environments were compared: unsensitized rats, rats immunosensitized with a primary infection of H. diminuta, rats immunosensitized with a primary infection of Nippostrongylus brasiliensis and mice concurrently infected with Heligmosomoides polygyrus. The specific activities of PK and PEPCK in whole worm extracts were similar in 10-, 21- and 35-day-old worms and did not differ in worms isolated from different host environments. However, the PEPCK/PK ratio is high in worms that utilize mitochondrial pathways and low in worms that produce predominantly lactate. LDH activity is high in lactate producers. It is concluded that the pattern of metabolism in H. diminuta is influenced by many effectors in the host environment.