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.
Hippulin
Hippulin, also known as Δ-14-isoestrone, as well as 14-isoestra-1,3,5(10),8-tetraen-3-ol-17-one, is a naturally occurring estrogen found in horses and an isomer of equilin. The compound, likely in sodium sulfate form, is a component of conjugated estrogens (Premarin), a pharmaceutical extract of the urine of pregnant mares, though it is present only in small amounts in pregnant mare urine. It has been reported by possess either equivalent estrogenic activity to that of equilin or only slight estrogenic activity. The compound was first described in 1932.