Prothoracicotropic hormone (PTTH) was the first insecthormone to be discovered. It was originally described simply as "brain hormone" by early workers such asStefan Kopeć (1922)[1] andVincent Wigglesworth (1934),[2] who realized thatligation of the head of immature insects could preventmolting orpupation of the body region excluded from the head if the ligation was performed before a critical age in the lifestage was reached. After a certain point the ligation had no effect and both sections of the insect would molt or pupate. However, implantation of aconspecific brain to asessile ligated abdomen or an abdomen underdiapause[3][4] would induce molting or pupation. Thus, the brain was originally thought to be the source of the hormone that induces molting in insects.
Later it was established that theinsect brain produces a number of hormones, but the hormone which was the cause of the observations made by Kopeć and Wigglesworth was prothoracicotropic hormone. PTTH is secreted by aneurohemal organ, thecorpus cardiacum (in some insects thecorpus allatum secretes PTTH) which is actually a discrete structure posterior to the brain. PTTH is released in response to environmental stimuli and as its name implies PTTH acts on theprothoracic glands, which respond by releasingmolting hormone (anecdysteroid) into thehaemolymph. Molting hormone stimulates the molting process.[5][6]
^Wigglesworth, V.B. (1934). "The physiology of ecdysis inRhodnius prolixus (Hemiptera). II Factors controlling moulting and metamorphosis".Q. J. Microsc. Sci.77:191–223.
