Grayanotoxin is a diterpenoid which is contained in the plants belonging to the family Ericaceae, such as Leucothoe grayana Maxim., Japanese Pieris (Pieris japonica (Thunb.) D. Don ex G. Don), Japanese Azalea (Rhododendron molle G.Don).
It is a neurotoxin which opens sodium channels in excitable cell membranes and sustains depolarization.   Therefore, it causes sustained depolarization of nerve terminal and influx of calcium ions at nerve endings to cause excessive release or depletion of Neurotransmitters.   The vagus nerve is stimulated first and paralyzed later.
Grayanotoxin is isolated from Leucothoe grayana Maxim. and identified.   Therefore grayanotoxin is named after the specific epithet, grayana.
Twenty kinds of grayanotoxins are now isolated and identified.   However, grayanotoxin I, II and III are heighly represented.   Grayanotoxin I, II and III have another names, such as andromedotoxin, grayanol and andromedol respectively.

 molecular formulamolecular weightCAS registry number
grayanotoxin IC22H36O7412.5234720-09-6
grayanotoxin IIC20H32O5352.4714678-44-8
grayanotoxin IIIC20H34O6370.4864678-45-9

grayanotoxin-1 grayanotoxin-2 grayanotoxin-3
grayanotoxin I grayanotoxin II grayanotoxin III

Natural compounds are often difficult to identify even if it is isolated.   Therefore, when a plant which the substance is isolated from is different, it is thought the substance is different and is given a different name after the plant name even if the substance is the same.
Other names of grayanotoxin;
Andromedotoxin :
isolated from Rhododendron maximum
Rhodotoxin :
isolated from Japanese Azalea (Rhododendron molle G.Don)
Asebotoxin :
isolated from Japanese Pieris
(Pieris japonica (Thunb.) D. Don ex G. Don)