2016 Lower GI Pharmacology

• motility and water absorption are often treated as separate processes, but they are interrelated
  • i.e., decreasing motility increases water absorption
• many drugs and hormones affect both processes - two key agents which regulate both aspects of lower GI function are:
• ACETYLCHOLINE (muscarinic receptors):
1. secreted by interneurons of the submucosal and myenteric plexi, as well as by pre- and post-ganglionic neurons of the parasympathetic branch of the autonomic nervous system
2. involved in many reflexes (and obviously represents the final common pathway)
3. increases both motility and secretion
• SOMATOSTATIN:
1. inhibits secretion of numerous hormones and transmitters, including:
• gastrin, cholecystokinin (CCK), glucagon, growth hormone, insulin, secretin, pancreatic polypeptide, vasoactive intestinal peptide and serotonin (5HT)
2. decreases intestinal and pancreatic secretion
3. decreases intestinal motility; inhibits gallbladder contraction
4. induces vascular smooth muscle contraction, reducing portal and splanchnic blood flow
5. inhibits secretion of some anterior pituitary hormones

MOTILITY

• MOTILIN is a "brain-gut" peptide secreted by cells in the small intestine and several brain regions
• in the GI tract, MOTILIN induces the migrating myoelectric complex
  • it also stimulates pepsin production

WATER ABSORPTION most water reabsorption occurs before the large intestine at the level of the large intestine, disruption of the balance between absorption and secretion results in diarrhea or constipation

• Motility&Absorption
• Enteric nervous system
• Drug/ENS interactions PPSX show