Motilin
Overview
Motilin is a 22-amino acid endogenous peptide hormone secreted by enteroendocrine cells in the duodenum and jejunum. It binds to motilin receptors on gastrointestinal smooth muscle and enteric neurons, stimulating phase III migrating motor complexes and promoting gastric emptying. The therapeutic rationale for exogenous motilin or receptor agonists includes treatment of gastroparesis and postoperative ileus. Erythromycin acts as a motilin receptor agonist, demonstrating the clinical relevance of this pathway.
Key Research Findings
Natural motilin itself has not been developed as a therapeutic due to rapid degradation and tachyphylaxis with repeated dosing. Synthetic motilin receptor agonists such as camicinal and mitemcinal have been evaluated in phase II trials for gastroparesis, with mixed results and concerns about receptor desensitization. Current clinical use of motilin pathway stimulation relies primarily on macrolide antibiotics rather than peptide-based agents.
Intravenous
Research Phase
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Octreotide (Sandostatin)
FDA ApprovedA synthetic octapeptide analog of somatostatin with a substantially longer half-life (90 minutes IV, 6 hours subcutaneous vs. 2 minutes for native somatostatin). Octreotide binds somatostatin receptors (primarily SSTR2 and SSTR5) to inhibit the secretion of GH, glucagon, insulin, gastrin, secretin, VIP, and other GI hormones. It reduces splanchnic blood flow, GI motility, and exocrine pancreatic secretion.
Lanreotide (Somatuline Depot)
FDA ApprovedA synthetic octapeptide analog of somatostatin with high affinity for SSTR2 and moderate affinity for SSTR5 receptors. Lanreotide is formulated as a supersaturated solution that forms a drug depot at the injection site, providing sustained release over 4 weeks. It inhibits GH secretion, GI hormone release, and has direct antiproliferative effects on neuroendocrine tumor cells through cell cycle arrest and apoptosis induction.
Pasireotide (Signifor)
FDA ApprovedA multireceptor-targeted somatostatin analog with high binding affinity for SSTR1, SSTR2, SSTR3, and SSTR5, particularly notable for its 40-fold greater affinity for SSTR5 compared to octreotide. This receptor profile makes pasireotide uniquely effective in Cushing's disease, where corticotroph adenomas predominantly express SSTR5. Pasireotide suppresses ACTH secretion from pituitary corticotroph tumors, reducing cortisol production.
Plecanatide (Trulance)
FDA ApprovedA synthetic 16-amino acid peptide structurally related to uroguanylin, an endogenous intestinal peptide that regulates fluid and electrolyte homeostasis in the GI tract. Plecanatide activates guanylate cyclase-C (GC-C) receptors on intestinal epithelial cells in a pH-dependent manner, preferentially in the proximal small intestine where pH is slightly acidic. GC-C activation increases intracellular and extracellular cGMP, stimulating chloride and bicarbonate secretion while reducing visceral pain signaling.