Many of the chemicals on that list are neurotransmitters that are not at all surprising. There is currently plenty of exciting research going on trying to link the brain and gut together. This blog article will focus on gastrin and how it relates to our digestion.

All About Gastrin

Hormones control a lot of our digestion, and one of the most important hormones for the proper functionality of upper gut is gastrin. Gastrin is a hormone that is released into our bloodstream by our stomach to help control digestion. Gastrin is produced by the G cells in the antrum of the stomach.¹ Gastrin release occurs because:^{2 3 4 5 6 7 8 9}

• The stomach body expands from consumption.
• Vagus nerve stimulation.
• Partially digested protein or amino acid supplements in the stomach.
• Hypercalcemia
• Ingestion of coffee and alcohol.
• H. pylori colonization of the antrum (stomach body).
• Using medications including adrenergic stimulating drugs, cholinergic agents, and H2 antagonists/PPI’s (negative feedback loop, reduction in stomach acid and increased stomach pH leads to increased gastrin levels in some people).
• The hormone bombesin, epinephrine, and gastrin-releasing peptide.
• Gastrin-producing tumors (gastrinoma).
• Zollinger-Ellison Syndrome

Gastrin, when it reaches the parietal cells of the antrum, signals the stomach to secrete gastric acid and release histamine. Gastrin does a lot to improve our digestion including:^{10 11 12 13 14 15 16}

• Causes the chief cells in the stomach to produce pepsinogen, which later becomes pepsin and helps to digest protein.
• Decreases upper stomach contractions and motility to help improve digestion by increasing stomach relaxation to allow ingestion of more food and further digestion by stomach acid and pepsin.
• Opens the pyloric sphincter and increases the rate of gastric emptying.
• Increases small intestine MMC function and helps relax the ileocecal valve.
• Induces pancreatic enzyme secretion.
• Stimulates bile release from the gallbladder.
• Helps regulate the production of gastric epithelial cells, tissue repair, and blood vessel growth in the stomach.

The body also has mechanisms to shut off production of the hormone when stomach digestion is completed. When the stomach pH is below three, gastrin production by the stomach is limited. Fasting also decreases gastrin levels. The pancreas releases somatostatin to inhibit gastrin and histamine in the intestinal tract to stop digestion in the stomach. Other hormones that slow down or stop production of the hormone include gastric inhibitory peptide, secretin, glucagon, and calcitonin. Finally, when most of the ingested food has gone from the stomach into the duodenum or has passed into the jejunum, the enterogastric reflex occurs to reduce gastric motility, gastrin release, and gastric acid production.^{17 18}

Gastrin and Proper Digestion

Having a less acidic stomach over time, like when you consume PPI’s or H2 antagonists, might explain the increase in serum gastrin levels and rebound acid reflux if you are on these medications long term or if you discontinue them abruptly. An increase of gastrin causes more stomach acid to be produced in a less acidic stomach for a short period of time, as a way for the body to try to correct digestion and compensate for the less acidic stomach. People with lower stomach acidity are more prone to upper gut overgrowth and combined with increased gastrin, and stomach acid production can lead to stomach distension, weakened LES, increased gastric pressure, and worsen reflux symptoms. Most of the time the doses of medication are increased, which further hinders stomach acid production, which increases gastrin production further, and the cycle repeats itself. Also, people with bile reflux see even worsening symptoms with up-regulation of gastrin because it also increases bile production and the opening of the pyloric sphincter, causing a mixture of bile and acid reflux which irritates the stomach and esophagus when fluxed, causing issues.^{19 20 21}

The body to ensure proper digestion in the upper gut should tightly regulate gastrin levels. To produce appropriate gastrin levels, you need to make sure that your calcium levels are balanced, reduction of upper gut overgrowth like H. pylori if you have it, and maintain proper stomach pH for digestion. When you are consuming food, you want to make sure that the pH of your stomach is less than three after you finish your meal. You can achieve proper stomach pH by ingesting betaine HCL, acidic foods, or digestive bitters towards the end of a meal if you can tolerate them to help accurately control gastrin production and aid with digestion.

There are several endogenous chemicals affect digestion including:

• Serotonin
• CCK
• GIP
• Gastrin
• Secretin
• Motilin
• Dopamine
• Acetylcholine
• Gaba
• Ghrelin
• Leptin
• Histamine
• Melatonin