Effect of vagotomy on biliary-tract motor activity in the opossum

In this study, we evaluated the effect of truncal vagotomy in the opossum on changes in gallbladder and sphincter-of-Oddi (SO) contractile activity that occur normally during fasting and after a meal. In six animals, bipolar electrodes were implanted on the SO, gastric antrum, duodenum, and jejunum. A catheter secured in the gallbladder fundus was used to monitor gallbladder volume. After control studies, truncal vagotomy and pyloroplasty were done in each animal. Before vagotomy, the SO exhibited cyclic changes in spike-burst rate, from 2 to 5/min, that were synchronized with corresponding phases of the duodenal MMC cycle. The gallbladder exhibited partial emptying during the second half of the duodenal MMC cycle with refilling during the first half of the next cycle. By two weeks after vagotomy, the MMC-related changes in SO and gallbladder contractile activity were normal. In contrast, vagotomy retarded the increase in SO spike-burst rate and delayed as well as diminished the pronounced gallbladder emptying that normally occurs after a meal. The same effects were observed for changes in SO and gallbladder activity induced by intraduodenal infusion of Isocal. After vagotomy, the SO and gallbladder exhibited exaggerated responses to intravenous infusion of CCK-OP or motilin. We conclude that truncal vagotomy in the opossum does not affect the fasting pattern of SO and gallbladder contractile activity, but it significantly alters the normal postprandial pattern of enhanced SO spike-burst rate and pronounced gallbladder emptying. The precise mechanism(s) whereby vagotomy produces these changes remains to be determined.