Epinephrine Inhibits Intestinal Motility
Among the listed options, epinephrine (C) is the substance that inhibits intestinal motility. This is supported by multiple lines of evidence demonstrating epinephrine's potent inhibitory effect on gastrointestinal motility.
Mechanism of Action of Epinephrine on Intestinal Motility
Epinephrine exerts its inhibitory effects on intestinal motility through several mechanisms:
- Epinephrine causes a reduction in motility associated with an increase in smooth muscle tone in the antrum of the stomach and duodenum 1
- It delays digestion of food in the small intestine and decreases propulsive contractions 1
- Propulsive peristaltic waves in the colon are decreased, which can result in constipation 1
- Epinephrine demonstrates the most potent inhibitory effect on intestinal peristalsis compared to other catecholamines 2
- It initially abolishes the response activity and prepotentials in intestinal smooth muscle cells, suppressing contractions without altering control activity or membrane potential 3
Comparison with Other Listed Options
Serotonin (5-HT)
- Contrary to inhibiting motility, serotonin generally promotes intestinal motility
- 5-HT4 receptor agonists like prucalopride are used to increase intestinal motility and treat constipation 4
Cholecystokinin (CCK)
- CCK stimulates gallbladder contraction and pancreatic enzyme secretion
- Not identified as an inhibitor of intestinal motility in the evidence
Motilin
- Motilin is a prokinetic hormone that stimulates intestinal motility
- Motilin agonists like erythromycin are used to improve motility in patients with dysmotility 4
Secretin
- Secretin primarily regulates pancreatic secretions
- Not identified as an inhibitor of intestinal motility in the evidence
Evidence Strength for Epinephrine's Inhibitory Effect
The inhibitory effect of epinephrine on intestinal motility is well-documented:
- In vitro studies on guinea pig ileum showed epinephrine had the strongest inhibitory effect on peristalsis compared to other catecholamines, being approximately 500 times more potent than dobutamine and dopexamine 2
- Electrophysiological studies demonstrate that adrenaline (epinephrine) inhibits intestinal motility by uncoupling control activity from response activity through suppression of prepotentials 3
- Norepinephrine, which has similar but less potent effects than epinephrine, has been shown to inhibit colonic contractions through α1A adrenoceptors 5
Clinical Implications
Understanding epinephrine's inhibitory effect on intestinal motility has important clinical implications:
- Patients receiving exogenous catecholamines, particularly epinephrine, for hemodynamic support may experience decreased intestinal motility as a side effect
- This can contribute to ileus, constipation, and feeding intolerance in critically ill patients
- When managing patients with constipation, consideration should be given to medications that may have adrenergic effects
In conclusion, among the options presented, epinephrine (C) is the substance that inhibits intestinal motility through its effects on intestinal smooth muscle, making it the correct answer to this question.