[9] Meanwhile, in concert with secretin's actions, the other main hormone simultaneously issued by the duodenum, cholecystokinin (CCK), stimulates the gallbladder to contract, delivering its stored bile.

[13] 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.

[15] However, British researchers George Oliver and Edward Albert Schäfer had already published their findings of an adrenal extract increasing blood pressure and heart rate in brief reports in 1894 and a full publication in 1895, making adrenaline the first discovered hormone.

[19] Secretin is synthesized in cytoplasmic secretory granules of S-cells, which are found mainly in the mucosa of the duodenum, and in smaller numbers in the jejunum of the small intestine.

[25] Cyclic AMP acts as second messenger in intracellular signal transduction and causes the organ to secrete a bicarbonate-rich fluid that flows into the intestine.

Bicarbonate is a base that neutralizes the acid, thus establishing a pH favorable to the action of other digestive enzymes in the small intestine.

In the absence of secretin or its receptor in the gene knockout animals, central injection of angiotensin II was unable to stimulate water intake and vasopressin release.

[12] It has been suggested that "Secretin as a neurosecretory hormone from the posterior pituitary, therefore, could be the long-sought vasopressin independent mechanism to solve the riddle that has puzzled clinicians and physiologists for decades.

It was found that both central and peripheral injection of Sct reduce food intake in mouse, indicating an anorectic role of the peptide.

[41][42][43] A high-affinity and optimized secretin receptor antagonist (Y10,c[E16,K20],I17,Cha22,R25)sec(6-27) has been designed and developed which has allowed the structural characterization of secreting inactive conformation.