Epinephrine Inhibits Intestinal Motility
Among the listed options, epinephrine (c) is the substance that inhibits intestinal motility. 1
Mechanism of Action of Each Substance
Epinephrine: Acts as a potent inhibitor of intestinal peristalsis by uncoupling the control activity to response activity through suppression of prepotentials in intestinal smooth muscle cells 2. It is approximately 500 times more potent at inhibiting intestinal motility compared to other catecholamines like dobutamine and dopexamine 1.
Gastrin: Not an inhibitor of intestinal motility. Gastrin primarily stimulates gastric acid secretion and has minimal effects on intestinal motility 3.
Cholecystokinin (CCK): Stimulates rather than inhibits intestinal motility. It primarily functions to stimulate gallbladder contraction and pancreatic enzyme secretion 3.
Motilin: Acts as a prokinetic agent that stimulates intestinal motility. Motilin receptor agonists like erythromycin are used to enhance gut motility in patients with gastrointestinal motility disorders 4.
Serotonin (5-HT): Generally promotes intestinal motility rather than inhibiting it. 5-HT4 receptor agonists like prucalopride are used as prokinetic agents to stimulate colonic peristalsis and enhance bowel motility 4.
Evidence Supporting Epinephrine's Inhibitory Effect
In comparative studies, epinephrine demonstrates the strongest inhibitory effect on intestinal peristalsis among catecholamines, with the rank order of inhibitory potency being: epinephrine > norepinephrine > dopamine > dobutamine ≈ dopexamine 1.
Electrophysiological studies show that epinephrine initially abolishes the response activity and prepotentials in intestinal smooth muscle cells, leading to inhibition of contractions 2.
The inhibitory effect of epinephrine on intestinal motility is mediated through alpha-2 adrenergic receptors, as demonstrated by studies showing that selective alpha-2 agonists delay small intestinal transit 5.
Clinical Implications
The inhibitory effect of epinephrine on intestinal motility explains why patients receiving epinephrine for shock or other indications may experience decreased gut motility 1.
Alpha-2 antagonists like atipamezole can reverse the inhibitory effects of alpha-2 agonists on intestinal motility, suggesting potential therapeutic applications for postoperative ileus 5.
Understanding the inhibitory effect of epinephrine on intestinal motility is important when managing critically ill patients who require catecholamine support, as this may contribute to ileus and feeding intolerance 1.
Comparison with Other Motility Modulators
Opioids also inhibit intestinal motility and are commonly used as antidiarrheal agents, with loperamide being the drug of choice due to its low risk of side effects 6.
Enkephalins and enkephalinase inhibitors have potent antisecretory properties in the intestine but their effects on motility are less pronounced compared to epinephrine 7.