In vitro excystation of Paragonimus heterotremus metacercariae

In vitro excystation studies were carried out on the metacercariae cysts of Paragonimus heterotremus obtained from naturally infected crabs Potamon sp p. The effects of elastase, trypsin, trypsin-dog bile, trypsin-bile salt, a nd dithiothreitol (DTT) were examined. The trypsin-dog bile medium stimulat ed maximum excystation. Of the media that contained 1 mM DIT, the optimum c onditions for the excystation were shown to be pH 9, temperature of 39-40 C , and osmolarity of 250-350 mOsm. The DTT acceleration was antagonized by a ll of the following 6 protease inhibitors: leupeptin (0.5-4 mug/ml), L-tran s-epoxysuccinyl leucylamido (4-guanidine) butane (1-8 muM), N-tosyl-Lphenyl alanine chloromethyl ketone (0.1-0.4 mM), N alpha -p-tosyl-L-lysine chlorom ethyl ketone (25-200 mug/ml), iodoacetic acid (0.5-4 mM), and phenylmethyls ulfonyl fluoride (1-4 mM). These results suggest that a number of extrinsic and intrinsic factors may modulate excystation.