Relationship between exsheathment and enzyme activity (alkaline phosphatase and leucine amino peptidase) during ageing of Trichostrongylus colubriformis infective larvae.

A stock of Trichostrongylus colubriformis infective larvae (L3) was stored for up to 15 weeks at 24 degrees C. At three weeks intervals, samples of L3 were taken to assess exsheathment rate and enzyme activity Leucine Amino Peptidase (LAP) and Alkaline Phosphatase (AP). From 0 to 9 weeks of storage, a decrease in enzyme activity was observed correlated with a decrease in exsheathment rate (percentage of L3 exsheathed in vitro after 20 min); the maximum percentage of exsheathed larvae (L3 exsheathed after 180 min) was then 75%. From 9 to 15 weeks of storage, both enzyme activity and exsheathment rate were low and constant; the maximum percentage of exsheathed larvae never exceeded 30%. The role of enzymes in the mechanism of exsheathment is discussed.