Cellular oxidative stress may promote damage or death in biological systems and may be caused by production of pro-oxidant molecules known as reactive oxygen species (ROS). The aim of this work was to analyze the activity of antioxidant enzymes (catalase [CAT], superoxide dismutase [SOD] and glutathione peroxidase [GPx]) in the shrimp Palaemonetes argentinus Nobili, 1901 infected by Probopyrus ringueleti (Verdi & Schuldt, 1987), a gill chamber parasite known for its capacity to cause host metabolic changes, including changes in oxygen consumption rates. Infested and non-infested shrimp were collected in the Patos Lagoon estuary (southern Brasil), where the prevalence of the parasite may be as high as 70%. No significant differences were observed for either CAT or GPx activities. However, SOD activity was significantly reduced in infected shrimp, suggesting that bopyrid isopod respiratory impairment resulted in reduced SOD enzyme activity.

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Reduced superoxide dismutase activity in Palaemonetes argentinus (Decapoda, Palemonidae) infected by Probopyrus ringueleti (Isopoda, Bopyridae).

The effect of Clinostomum detruncatum meta- cercaria infection on the activities of the antioxidant enzymes superoxide dismutase and catalase in muscle of the fresh- water fish Rhamdia quelen was analyzed. Tert-butyl hydro- peroxide-initiated chemiluminescence, a measure of lipid peroxidation, was also investigated. Enzyme activities were similar in infected and uninfected fishes. However, the chemi- luminescence was almost 2-fold higher in muscle of infected fishes than in muscle of uninfected ones. These results indi- cate that parasite infection induces oxidative stress and a higher level of membrane damage in the fish muscle due to an imbalance between pro-oxidants and non-enzymatic anti- oxidants. Our results suggest that fish response to parasite infection could involve, as in other vertebrates, reactive oxy- gen intermediates.

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Lipid peroxidation induced by Clinostomum detruncatum in muscle of the freshwater fish Rhamdia quelen.

Susceptibilities of various molluscan hosts to different strains of the parasites were reviewed. Cellular reactions following host-parasite associations were elucidated. Moreover, metabolic similarities, integration and biochemical adaptation of the parasite and host were also investigated in an attempt to elucidate factors affecting the host-parasite relationship.

Factors affecting natural selection between helminth parasites and their molluscan intermediate host with special reference to Schistosoma

The activities of catalase (H2O2-oxidoreductase EC 1.11.1.6)- and glutathione reductase (EC 1.6.4.2) as two important scavenger enzymes, were measured in tissue homogenates of Biomphalaria alexandrina and Bulinus truncatus, the snail vectors of Schistosomiasis. A parallel study was done on Lymnea truncatula snails which are not susceptible to Schistosoma infection. The apparent Michaelis constant (Km) for both anzymes were determined in tissue homogenates of the three studied species. The results obtained showed that both susceptible species have higher affinity to hydrogen peroxide (H2O2) and oxidized glutathione (GSSG) than the non-susceptible one.

A. El Ansary

Papers

Kinetic potentials of certain scavenger enzymes in fresh water snails susceptible and non-susceptible to schistosoma infection