Structure-activity relationship of herbicides inhibiting ACh-induced contractions in a molluscan smooth muscle

Certain herbicides are known to influence the muscle function of molluscs. The penis-retractor muscle complex (PRM complex) of the edible snail, Helix pomatia, is a suitable test object for studying these side effects in smooth muscle, because sequential contractions can be induced in vitro by adding and removing acetylcholine (ACh). In the presence of herbicidal amides, carbamates, and ureas (concentration, 10^?4 mol/liter) the muscle tension was found to be reduced to a variable extent. In contrast, the relaxing effect of herbicidal phenoxycarbonic acids was weak. The inhibitory properties of the herbicides tested were correlated with the electron-withdrawing properties of certain substituents. These substituents are bound to an amino function. Their structure is either aromatic (amides, biscarbamates, carbamates, ureas), aliphatic (thiocarbamates), or cycloaliphatic (cycloat). The structure-activity relationship is comparable with that found for herbicidal activity in plants.