In the present report we study the proteolytic activity of the excretion-secretion and crude extracts of different stages of Trichinella spiralis (Owen, 1835) Railliet, 1895, (muscle-stage larvae, adult worms before and after mating, and newborn larvae) using natural substrates (structural and hematic mammalian proteins). The analysis of the results allow us to set up a certain stage-specificity, as well as an important relationship between the protease patterns throughout the parasite life cycle and how the parasite may overcome both mechanical and humoral barriers within the host. Muscle-stage larvae present a great activity against structural proteins (collagen), while newborn larvae and adult worms degrade principally hematic proteins (hemoglobin, fibrinogen and immunoglobulin G).
Chlorophyll content, photosynthetíc oxygen evolution and the activities of ATP- sulphurylase (ATP-s) (E.C. 2.7,7.4.), OAS-sulphydrylase (OAS-s) (E.C, 4.2.99.8.), nitráte reductase (NR) (E.C. 1.6.6.1.) and glutamine synthetase (GS) (E.C. 6.3.1.2), were determined in leaves of Zea mays L. Dekalb cv. Sponsor plants grown in the presence of 0, 10, 100, 250 pM Cd in order to evaluate the effect of this metal on sulphate and nitráte assimilation pathway. Cd induced a slight decrease of photosynthetíc oxygen evolution (-21 % of the control at 250 pM), whereas the enzyme activities were differently influenced: OAS-s and GS increased up to 40 and 25 % of the control, respectively, at 250 pM Cd; NR showed a 20 % stimulation at 100 pM Cd, and ATP-s was slightly inhibited. The results stress the importance of experimental conditions adopted on the response of enzyme activities to Cd and suggest that the observed increases of enzyme activities are related to a defence mechanism.
Experimental infection of the pulmonate snails Arianta arbustorum L. and Helix pomatia L. with first-stage larvae of protostrongylid nematode Elaphostrongylus cervi Cameron, 1931 was performed in order to determine modes of larval entry into the body of the snail intermediate host. Groups by four individuals of both snail species were examined histologically 30, 60, 90, and 120 minutes after the beginning of exposure and 1, 2, 4, and 7 days post infection. All 64 snails examined were found to be successfully infected. The superficial furrows of the sole were recognized as the most important site of larval entry into the snail organism. Larval penetration was observed to be accompanied by destruction of the superficial epithelium. The number of larvae found in the subepithelial connective tissue of the headfoot was significantly higher than that found in other tissues and organs. Larval counts in individual parts of the body of snails examined from 0 to 7 days p.i. did not fluctuate significantly. The present results indicate that only those protostrongylid larvae which actively penetrated the superficial epithelium of the snail sole play an important role in the life cycle.