I have two different papers. One claims that gut motility is reduced by stimulation of the Opioid κ and δ receptors. The receptors are activated by Morphine and certain derivatives, specifically Codeine, Fentanyl, Hydromophone, Methadone, and Oxycodone.

The second paper claims that gut motility is reduced by blocking the 5-HTb3 receptors. Antagonists or competitors to the 5-HTb3 receptors being Morphine and certain derivatives.

Are these two different theories, two different action mechanisms, or am I missing something?


2 Answers 2


When discussing the control of gut motility there is more to mention than the use of serotonergics and opioids - a number of peptide and nonpeptide neurotransmitters are important. Somatostatin and nitric oxide are two examples which each happen be inhibitory of intestinal motor function, but by two completely different mechanisms. A bit of understanding in cell biology, specifically cell signalling would be helpful to fully grasp this, but the former acts by inhibiting the release of Acetylcholine and Substance P while the latter increases levels of cAMP/cGMP. And don't forget about the basics when it comes to motor control - the cholinergics and adrenergics (including dopamine) are logical opposites.


Leung, P.S. 2014, The Gastrointestinal System: Gastrointestinal, Nutritional and Hepatobiliary Physiology, Springer, 19/03/2018, http://www.springer.com/cda/content/document/cda_downloaddocument/9789401787703-c2.pdf?SGWID=0-0-45-1491980-p176563984

  • $\begingroup$ This is a nice answer about gut motility, but the body of the question specifically asks about opioids and opiates, which you don't address at all. I don't mean to be condescending, but there's more to a question than just the title. I see you're new (Welcome!) Maybe you're not too familiar with the SE model? In any case, nice to have you here. $\endgroup$ Mar 19, 2018 at 23:23
  • $\begingroup$ Hi, looking back at my answer I didn't really address serotonin either, thanks for the feedback. Can you tell me more about the SE model? $\endgroup$ Apr 21, 2018 at 9:14

They are two different mechanisms.

Opium is arguably one of the oldest herbal medicines, being used as analgesic, sedative and antidiarrheal drug for thousands of years. These effects mirror the actions of the endogenous opioid system and are mediated by the principal μ-, κ- and δ-opioid receptors. In the gut, met-enkephalin, leu-enkephalin, β-endorphin and dynorphin occur in both neurons and endocrine cells. When released, opioid peptides activate opioid receptors on the enteric circuitry controlling motility and secretion. As a result, inhibition of gastric emptying, increase in sphincter tone, induction of stationary motor patterns and blockade of peristalsis ensue. Opioid receptors in the gastrointestinal tract

Roles of 5-HT in health include control of normal gut motor activity, secretion, and sensation, and regulation of food intake and cell growth. Abnormalities of serotonergic function contribute to symptom genesis in functional bowel disorders, inflammatory and infectious diseases of the gut, emetic responses to varied stimuli, obesity, and dysregulation of cell growth. Therapies acting as agonists or antagonists of 5-HT receptors or that modulate 5-HT reuptake play prominent roles in managing these conditions... Serotonin and the GI tract.

  • $\begingroup$ Interesting. Gives me some more reading to do. I assume at this time, the opioid receptors only work in one direction, to slow the gut. Because not taking morphine does not cause diarrhea, but too much serotonin such as in carcinoid syndrome does cause diarrhea. $\endgroup$
    – DcShank
    Oct 26, 2014 at 16:31
  • $\begingroup$ Don't rule out endorphins and their receptors in the GI tract. $\endgroup$ Oct 26, 2014 at 16:34
  • $\begingroup$ What really burns me is that a treatment exists for IBS and depression that really works, Tianeptine (a serotonin re-uptake enhancer). But is not legal in the US. I have a trip planned next week to Nogales, Mexico. $\endgroup$
    – DcShank
    Oct 26, 2014 at 17:09

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