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Acute effects of morphine on rat intestinal motility
Abstract:
Systemic injection of morphine (0.5-16 mg/kg) caused dose-related increases in intestinal intraluminal pressure in anesthetized rats. Injection of morphine into cerebral ventricles was no more effective than the intravenous (i.v.) route. Decapitation of the animals did not prevent the intestinal stimulatory effect of i.v. morphine. The intestinal stimulation induced by i.v. morphine and 5-hydroxytryptamine (5-HT), but not that induced by cholecystokinin octapeptide, was antagonized by methysergide. Morphine appears to stimulate contractions of intestinal circular muscle in the rat by release of local, endogenous 5-HT.
Insights
Morphine increases intestinal pressure in rats by releasing serotonin (5-HT). This effect is mediated locally within the gut, not by the central nervous system. Methysergide blocks this morphine-induced intestinal stimulation.
Area of Science:
- Pharmacology
- Gastroenterology
- Neuroscience
Background:
- Opioids like morphine are known to affect gastrointestinal motility.
- The precise mechanism by which morphine influences intestinal pressure is not fully understood.
- Previous research suggests a role for serotonin in opioid-induced gastrointestinal effects.
Purpose of the Study:
- To investigate the mechanism of morphine-induced intestinal stimulation in rats.
- To determine if the central nervous system mediates the intestinal effects of morphine.
- To explore the role of endogenous serotonin in morphine's action on the gut.
Main Methods:
- Systemic and intracerebroventricular injections of morphine in anesthetized rats.
- Measurement of intestinal intraluminal pressure.
- Administration of 5-hydroxytryptamine (5-HT) and cholecystokinin octapeptide.
- Antagonism studies using methysergide.
Main Results:
- Systemic morphine administration caused a dose-dependent increase in intestinal intraluminal pressure.
- Intracerebroventricular morphine injection was not more effective than intravenous administration.
- Decapitation did not abolish the intestinal stimulatory effect of intravenous morphine.
- Methysergide antagonized the intestinal stimulation induced by morphine and 5-HT, but not cholecystokinin octapeptide.
Conclusions:
- Morphine stimulates intestinal circular muscle contractions in rats.
- This stimulation is mediated by the release of local, endogenous 5-hydroxytryptamine (5-HT).
- The effect of morphine on the intestine does not appear to be centrally mediated.