Phenthoate (O, O-dimethyl S-alpha ethoxy carbonylbenzyl phosphorodithioate) was studied
for its pharmacodynamic effects on blood pressure in dog, isolated frog heart, skeletal muscle
(frog rectus abdominis) and smooth muscle (guinea pig ileum). Phenthoate did not produce
consistent effect on blood pressure of dog. No effect on resting tone of skeletal and smooth
muscle preparations was observed. Phenthoate neither inhibited nor potentiated the acetylcholineinduced contractions of skeletal muscles. However, it blocked non-specifically the acetylcholine, histamine, 5-hydroxytryptamine and barium chloride-induced contractions of guinea pig ileum. Phenthoate produced negative inotropic and chronotropic effect on isolated frog heart which was blocked by atropine, indicating the cholinomimetic effect as a result of cholinesterase inhibition which is the characteristic feature of organophosphorous compounds.