Secretin
Secretin was the first hormone to be identified. In 1902, William Bayliss and Ernest Starling were studying how the nervous system controls the process of digestion. It was known that the pancreas secreted digestive juices in response to the passage of food (chyme) through the pyloric sphincter into the duodenum. They discovered (by cutting all the nerves to the pancreas in their experimental animals) that this process was not, in fact, governed by the nervous system. They determined that a substance secreted by the intestinal lining stimulates the pancreas after being transported via the bloodstream. They named this intestinal secretion "secretin". Secretin was the first such "chemical messenger" identified. This type of substance is now called a hormone, a term coined by Bayliss in 1905.
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.