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.
Estradiol benzoate
Estradiol benzoate was one of the first estrogens to be developed and marketed. In 1931, Adolf Butenandt found that the benzoic acid ester of estrone had a prolonged duration of action. Schwenk and Hildebrant discovered estradiol via reduction of estrone in 1933, and they proceeded to synthesize estradiol benzoate from estradiol the same year. Estradiol benzoate was patented by Schering in 1933, and then by Schering-Kahlbaum in 1936 in an oil preparation for injectable use, and was introduced later that year in 1936 under the brand name Progynon-B. Following its introduction, estradiol benzoate, along with estradiol dipropionate, were the most widely used esters of estradiol for many years. However, estradiol valerate and estradiol cypionate, which are longer-acting esters that require less frequent administration, were developed and introduced in the 1950s, and have since largely superseded estradiol benzoate and estradiol dipropionate.