Prothoracicotropic hormone
Prothoracicotropic hormone (PTTH) was the first insect hormone to be discovered. It was originally described simply as "brain hormone" by early workers such as Stefan Kopeć (1922) and Vincent Wigglesworth (1934), who realized that ligation of the head of immature insects could prevent molting or pupation 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 a conspecific brain to a sessile ligated abdomen or an abdomen under diapause would induce molting or pupation. Thus, the brain was originally thought to be the source of the hormone that induces molting in insects.
Miguel Ondetti
Miguel Ondetti moved to the gastrointestinal hormone group in the mid 1960s. The first hormone to be studied by Ondetti's group was cholecystokinin, a digestion hormone. This product presented unique challenges because of the small amounts used in reactions. Unfortunately, bioassays were not quantitative enough to use for results and chemical reactions did not run well as such low amounts.