Effect of analgesic drugs on the electromyographic activity of the gastrointestinal tract and sphincter of Oddi and on biliary pressure.

Continuous biliary pressure and electromyographic activity of the sphincter of Oddi and gastrointestinal tract were recorded in conscious opossums following administration of analgesic drugs. Morphine, meperidine, and pentazocin increased significantly the duration of the migrating motor complex (MMC) cycle. Periods of 1-2 minutes of intense burst of spike potentials were seen in the sphincter of Oddi and duodenum following administration of morphine (8 experiments), meperidine (6 experiments), and pentazocin (3 experiments). The biliary pressure in the control studies was similar to that following administration of all analgesics in the animals with gallbladder and following instillation of tramadol, metamizol, and acetylsalicylic acid in animals with no gallbladder. However, the biliary pressure was significantly higher following administration of morphine, meperidine, and pentazocin in the animals with no gallbladder. It is concluded from this study that morphine, meperidine, and pentazocin may cause important disturbances in the motility of the sphincter of Oddi and gastrointestinal tract. These myoelectric disturbances may cause an increase in the biliary pressure in animals that have been subjected to cholecystectomy, but not in animals with intact gallbladder. The gallbladder may accommodate the bile produced by the liver during periods of sphincter of Oddi dysfunction and thus impede an increase in the biliary pressure.