Dr. Murai Éva szerk.: Parasitologia Hungarica 16. (Budapest, 1983)
and that inhibition arises solely from the tegument activity of viable worms, presumably due to a weak binding bringing about configurational changes in the enzyme which are unfavourable for the catalytic processes. MATERIALS AND TVIETHODS Plerocercoid larvae and adults of Ligula intestinalis (L. , 1758) (Diphyllobothriidae) , tetrathyridium larvae of Mesocestoides corti (Hoepli, 1925) (Mesocestoididae), and adult specimens of Fasciola hepatica (L. , 1758) (Fasciolidae) were used in the present studies. The plerocercoid larvae of L. intestinalis were obtained from freshly caught breams (Abramis brama), roaches (Rutilus rutilus) and spiny loaches (Cobitis taenia). The tetrathyridium larvae of Mesocestoides corti were obtained from a laboratory worm strain maintained artificially in albino mice. Adult specimens of the liver fluke ( F. hepatica) were collected from biliary vessels of naturally infected cattle at an abattoir. The collected specimens of all worm species were washed 3-5 times in sterile physiological saline or in Tyrode or Krebs-Ringer-Tris solutions (READ, ROTHMAN and SIMMONS, 1963). After washing the wet mass of the worms was weighed. After washing, plerocercoid larvae of L. intestinalis and adults of the liver fluke were rinsed with sterile distilled water, then homogenized (Omni-Mixer Homogenizer, Sorval Inc.) in a 0. 17 M Tris-HCl buffer five times their body mass, pH 7.2, containing 8. 3 mM CaCl 2 , or in distilled water. The homogenate was centrifuged with 19 500 g at 5°C for 60 min, and the resulting supernatante was used for further studies. Determination of lipase activity was performed on tributyrin substrate using pH-Stat (Radiometer, PHM 62 Standard pH meter, REA 61 Titrigraph Module, REC 61 Servograph, ABU 12 Autoburette). The emulsion composition of substrate was the following: Ten ml of tributyrin + 10 g gum arabic were homogenized in 70 ml distilled water, then the pH of the emulsion was adjusted to 8. 0, and it was filled up to 100 ml with distilled water. The determinations were carried out at room temperature, with a total volume of 1 0 ml. At the examination of worm extracts and maintenance media, the measuring mixture contained 1 ml test material and 9 ml substrate. The unit of lipase activity was defined as the fatty acid quantity (umol) produced by decomposition of substrate in 1 min. With certain test materials, lipase activity determination was performed also according to the method of RUFF and READ (1973) with triolein substrate. Substrate decomposition was determined on the basis of change in optical density read at 660 nm 5 min after the addition of the sample tested. The measuring mixture contained 1 ml substrate and 1 ml test material. On N-methyl-indoxyl-myristate substrate, lipase activity was determined according to the method of GUILBAULT et al. (1969) as modified by RUFF and READ (1973). Determinations were done by a Unicam SP 1 800 Ultraviolet spectrophotometer equipped with fluorometer, using Ilford 303 turquoise filter and-inductive light of 420 nm wavelength. Emission was read at 490 nm. Enzyme activity is expressed in percentile terms of relative fluorescence. For enzyme-histochemical studies the washed worms were fixed in a formol-saccharose fixing mixture adjusted to pH 7.5 with Sörensen's buffer mixture, at 4°C. Sections were cut by freezing microtome. Lipase activity was demonstrated using GÖMÖRI' s (1952) method.
