Tissue sensitivity to acetylcholine, adrenaline, noradrenaline and serotonin and agents acting on sulphydryl groups.

Parachloromercury benzoate (PCMB), a sulphydryl inactivator, caused a progressively increasing inhibition of tissue responses to acetylcholine, adrenaline, noradrenaline and serotonin in vitro. This inhibition was progressively and completely reversed by penicillamine, a sulphydryl activator. It is inferred that intact sulphydryl groups are essential for constancy of responses of excitable tissues to the neurotransmitters.