Secretin is a hormone that improves digestion while protecting the stomach and the gut. Abnormal secretin levels may be diagnostic of pancreatic disorders; this hormone also has an impact on fluid balance, other digestive hormones, the heart, brain, and lungs. Read on to learn more about the different roles that secretin plays in our bodies.
Secretin is a peptide hormone produced by gut cells (S cells of the small intestine) in response to gastric acid .
It was the first hormone to be discovered in the early 1900s and has been found in humans, mice, rats, dogs, pigs, and other mammals .
Secretin shows biological effects by interacting with secretin receptors. These are found in the heart, kidneys, stomach, and lungs .
Secretin stimulates the secretion of other substances. It helps digestion by causing the stomach to make pepsin, prompting the liver to make bile, and causing the pancreas to make digestive juices .
In addition, this hormone is important for processes that are involved in water/fluid balance .
Finally, it also functions as a neurotransmitter (chemical messenger) in the brain .
Basically, secretin is released in response to a low pH (below 4.0) .
Secretin has many complex and interconnected effects in the human body. This section will break them down in more detail.
This hormone reduces increased stomach acid secretion after a meal to protect the gut tissue .
In a clinical study performed on 6 healthy humans, secretin inhibited stomach acid secretion stimulated by pentagastrin, an analog of natural gastrin .
Secretin works by:
- Increasing somatostatin, a hormone that decreases stomach acid secretion. Secretin increased somatostatin in rats and dogs [14, 2].
- Increasing prostaglandin E2 (PGE2) [15, 14].
- Acting through the vagus nerve to increase the secretin binding sites .
- Decreasing gastrin production. Excessive production of gastrin and stomach acid causes stomach ulcers, damage to stomach lining cells, and bleeding [17, 18].
In H. pylori infection, some people develop ulcers while others don’t. H. pylori infection causes secretin deficiency and this lack of secretin may be the factor that causes peptic ulcers in these people .
Secretin also inhibits gut contractions, which reduces gut pressure and slows down the emptying of stomach liquids. This reduces the acidity in the gut, thus protecting the tissue .
An acidic condition in the intestine increases secretin production. Secretin gives an inhibitory signal to the brain for reducing acid release and gut flow to protect the intestine .
In mice, high levels of secretin were associated with slower stomach emptying .
Secretin protects stomach tissue by increasing mucus production. It promoted mucus production in rat gut cells, where this mucus formed a protective gel layer .
Secretin increased mucus production via cAMP .
Pancreatic enzymes are important for the digestion process in the gut (small intestine) .
Secretin increased pancreatic bicarbonate concentration by increasing the production of cAMP .
Bile is produced by the liver and helps digest fat in the small intestine.
Secretin increases pepsin production in the stomach, which helps digestion by breaking down ingested proteins into smaller peptides .
However, later studies indicate that secretin actually has antidiuretic properties. Studies in rats showed that secretin acts on kidney receptors to decrease urine production through adenylate cyclase activation. Also, actions of secretin in mice lacking secretin receptors confirmed its antidiuretic action .
In another study in rats, secretin showed a direct effect on kidney water reabsorption .
In secretin receptor-deficient mice, there was increased thirst, urination, and reduced water reabsorption .
Secretin acts on the brain’s secretin receptors to increase water intake. It works in combination with Angiotensin II. It increased water intake in mice when administered directly to the brain .
Secretin acts as a neurotransmitter in the brain.
Oxytocin plays an important role in social behavior. Secretin increased oxytocin release in the brain and, thus, increased social behavior in rats .
Secretin has a direct action on Purkinje neurons in the cerebellum of the brain. Purkinje neurons play a major role in motor coordination and learning.
Mice lacking secretin have reduced motor coordination and motor learning ability .
In another study, the administration of secretin through the nose improved motor behavior and reduced hyperactivity in mice .
Secretin acts as a neurotransmitter in the brain and it has a growth-helping effect on the neurons in mice .
Secretin-deficient mice had fewer new neurons, as more neuron-producing cells were dying .
In another study, secretin-deficient mice showed a reduced activity of the neuronal synapses in the hippocampus, indicating a role for secretin in brain function and development .
Secretin increases heart activity by increasing cAMP.
In another study, secretin increased the heart function and blood flow in pigs by acting through beta-adrenoceptors and by increasing nitric oxide release .
Secretin receptors are also detected in human lungs .
In 16 human lung tissue donors, secretin relaxed airway smooth muscles (it caused bronchial relaxation), suggesting a helpful role in increasing air supply in the lungs .
It may, therefore, be beneficial in asthma and allergies.
The hypothalamus plays an important role in appetite control. It is where the feeding and satiety centers are .
Schizophrenia causes major cognitive and motor disabilities. One such disability is associative learning. It can be evaluated by eye blinking activity. In a double-blind clinical study of 25 patients with schizophrenia, secretin given under the skin improved eye motor activity better than placebo treatment .
However, in another study of 22 patients with schizophrenia treated with intravenous secretin, there was no significant difference between secretin and placebo, although some individuals did show clinically meaningful improvement .
During cholestasis (impaired bile flow), secretin receptors increase in quantity. Increased secretin activity leads to increased bile duct cell growth and ultimately liver damage. In mice with cholestatic liver injury, secretin receptor blockers reduced bile duct cell growth and liver damage .
ZES is a condition that causes excessive gastrin production and damaging effects to the stomach tissue. Secretin significantly stimulated gastrin release from the gastrinoma cells of a patient with ZES .
Secretin treatment increased gastrin levels is Zollinger-Ellison patients, but reduced gastrin levels in duodenal ulcer patients. Thus, the secretin challenge test is a very useful tool to differentiate between ZES vs. non-ZES patients .
Cortex, a brain region important for cognitive function and environmental awareness, has secretin receptors. The use of secretin in the rat brain showed activation of the cortex . Therefore, people thought that secretin may help with autism.
In a single clinical study, 3 children with autism treated with secretin for 5 weeks showed a significant improvement in symptoms, including behavior, eye contact, and language .
Lafutidine, a drug used to treat stomach ulcers, reduces secretin levels. A single oral dose of Lafutidine reduced blood secretin levels in healthy human volunteers .
Gastrin is a hormone that stimulates stomach acid production. Cells in the stomach, intestine, and pancreas release gastrin .
Secretin suppressed food-stimulated gastrin secretion and stomach acid production in 22 human subjects .
However, gastrin also inhibits secretin action. It inhibited the release of secretin in rats by interacting with CCK-B receptors in liver cells. This reduced secretin receptors and related cAMP levels in rats .
Gut cells release CCK. This hormone is responsible for the stimulation of the gallbladder and releases bile into the intestine for the digestion of fats and proteins. It also stimulates pancreatic enzyme secretion.
In a clinical study, secretin played a dual role in insulin secretion in healthy humans. It directly increased insulin secretion and also prolonged the effect of insulin .
In another study in humans, intravenous secretin increased insulin release, immediately reaching high levels .
This is a test that is used to diagnose pancreas-related disorders and diseases such as inflammation or tumors. It is a measurement of the ability of the pancreas to respond to secretin by releasing substances like bicarbonate and trypsin into the pancreatic juice within the intestine .
In this test, the patient receives secretin through the nose or throat via a tube (that goes into the small intestine and stomach), or directly into a vein. After 1 – 2 hours, blood levels of pancreatic secretions are evaluated as a measurement of pancreatic function .
Abnormal levels of pancreatic secretions would suggest that there are problems in the pancreas.
FDA-approved secretin (by injection) is a diagnostic agent for stimulating the pancreas to help detect pancreatic problems. Secretin is given only by or under the supervision of a medical doctor, such as a diagnostic for illnesses .
Do not under any circumstances attempt to self-administer secretin for any reason.