Characterization of chemical stimuli for the penetration of Schistosoma mansoni cercariae. II. Conditions and mode of action.

The mode of action of chemical substances which trigger the penetration of S. mansoni cercariae into agar substrata is studied. The effectiveness of these substances is largely independent on their polarity and water solubility. Thus, they do not seem to act by a passive membrane permeation process, but they may interact with specific receptor sites, which are characterized. The receptor sites seem to respond to the following chemical characteristics of the stimulating aliphatic hydrocarbon chain: Carboxylic end group, lipophilic end group, chain length, cis-double bond. The penetration stimulating substances cause, even in cercariae in free water, a transformation of the tegument, manifested as a reduction of the Cercarienhüllen-Reaktion and a loss of osmotic protection.