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The possible involvement of adrenoceptors in the intestinal effect of morphine in mice
Abstract:
The inhibitory effect of morphine on intestine was observed by following the intestinal transit of a charcoal meal. This inhibitory effect of morphine was antagonized by naloxone. In addition, the inhibitory effect of morphine was also suppressed by prior administration of yohimbine and phentolamine. However, prazosin, a selective alpha 1-adrenoceptor antagonist, had no effect on the inhibitory effect of morphine on intestinal transit. Furthermore, prior administration of propranolol did not alter this effect of morphine. These adrenoceptor antagonists by themselves, at the doses used, had no effect on the rate of intestinal transit of a charcoal meal in mice. These results suggest that alpha 2-adrenoceptors may be involved in the intestinal effect of morphine while alpha 1- and beta-adrenoceptors do not appear to play any significant role in this aspect of morphine action.
Insights
Morphine inhibits intestinal transit, an effect blocked by naloxone. This action is suppressed by alpha-2 adrenoceptor antagonists, suggesting their involvement in morphine
Area of Science:
- Pharmacology
- Gastroenterology
- Neuroscience
Background:
- Opioids like morphine are known to affect gastrointestinal motility.
- The precise mechanisms underlying morphine's effect on intestinal transit are not fully elucidated.
- Adrenoceptors play a role in regulating various physiological processes, including gut function.
Purpose of the Study:
- To investigate the role of adrenoceptors in mediating the intestinal inhibitory effects of morphine.
- To determine which specific adrenoceptor subtypes are involved in morphine's action on intestinal transit.
Main Methods:
- The study utilized a charcoal meal assay in mice to assess intestinal transit time.
- Various adrenoceptor antagonists, including naloxone, yohimbine, phentolamine, prazosin, and propranolol, were administered prior to morphine.
- The effects of these antagonists on morphine-induced inhibition of intestinal transit were evaluated.
Main Results:
- Morphine significantly inhibited intestinal transit, which was antagonized by naloxone.
- Prior administration of yohimbine and phentolamine (alpha-2 adrenoceptor antagonists) suppressed morphine's inhibitory effect.
- Prazosin (alpha-1 adrenoceptor antagonist) and propranolol (beta-adrenoceptor antagonist) did not affect morphine's action on intestinal transit.
- The tested adrenoceptor antagonists alone did not alter normal intestinal transit.
Conclusions:
- Alpha-2 adrenoceptors are likely involved in mediating the intestinal inhibitory effects of morphine.
- Alpha-1 and beta-adrenoceptors do not appear to play a significant role in this specific action of morphine.
- These findings contribute to understanding the complex pharmacology of morphine in the gastrointestinal tract.