Category: signaling
Gut motility + secretion under multiple receptor controls. μ-opioid receptors on enteric neurons slow transit (constipating side effect of opioids; therapeutic for diarrhea via loperamide which is P-gp-extruded from brain). 5HT3 antagonism slows motility + reduces secretion; 5HT4 agonism (prucalopride — not in registry) increases motility. CFTR + guanylate cyclase C activators (lubiprostone — ClC-2; linaclotide + plecanatide — GC-C) increase intestinal chloride/water secretion → laxation. Osmotic laxatives (PEG, lactulose) draw water in by oncotic gradient. Bulk laxatives (psyllium not in registry). Antispasmodics (dicyclomine, hyoscyamine — anticholinergic) reduce smooth-muscle tone. Anti-emetics covered in serotonin (5-HT3) + dopamine (D2) pathways.