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Morphine: a dual effect at the canine choledochoduodenal junction
The Journal of Pharmacology and Experimental Therapeutics
|October 1, 1981
Summary
Morphine sulfate affects choledochoduodenal junction resistance, showing dose-dependent stimulatory and inhibitory effects. Higher doses relax, while lower doses cause spasms, suggesting complex mechanisms involving acetylcholine.
Area of Science:
- Gastroenterology
- Pharmacology
- Physiology
Background:
- The choledochoduodenal junction regulates bile and pancreatic juice flow into the duodenum.
- Opioids like morphine are known to affect gastrointestinal motility and sphincter function.
Purpose of the Study:
- To investigate the effects of morphine sulfate on resistance to flow through the canine choledochoduodenal junction.
- To elucidate the dose-dependent actions and underlying mechanisms of morphine on this junction.
Main Methods:
- Acute preparation of dogs anesthetized with pentobarbital.
- Intravenous bolus injections of morphine sulfate at varying doses.
- Administration of neostigmine, atropine, vagotomy, and reserpine for mechanistic studies.
- Naloxone challenge to assess opioid receptor involvement.
Main Results:
- Morphine exhibited a dual effect: stimulatory at lower doses (0.1 mg/kg) and inhibitory/relaxing at higher doses (1.0 mg/kg).
- Neostigmine potentiated the inhibitory effect, while atropine or vagotomy enhanced the stimulatory effect.
- Naloxone challenge induced strong contractions, suggesting opioid-mediated effects, which were blocked by atropine in neostigmine-treated dogs.
Conclusions:
- Morphine sulfate has complex, dose-dependent effects on the canine choledochoduodenal junction, involving both stimulatory and inhibitory pathways.
- Acetylcholine release may play a role in the inhibitory effects of morphine at this junction.
- These findings have implications for understanding opioid-induced changes in biliary and pancreatic outflow.