Regulation of fasting canine duodenal bile acid delivery by sphincter of Oddi and gallbladder

Abstract

Bile delivery into the duodenum during fasting is rhythmic and coordinated with the migrating myoelectric complex (MMC). To determine the role of the sphincter of Oddi (SO) and gallbladder (GB) in regulating duodenal bile acid delivery, three dogs were surgically prepared with a duodenal cannula and eight bipolar electrodes implanted from the duodenum to the terminal ileum. Fasting intestinal myoelectric activity was recorded during continuous intravenous infusion of [14C]taurocholic acid (TCA). Duodenal delivery of TCA was quantitated under four conditions: indirectly with the SO intact monitoring output with duodenal marker perfusion and directly with the SO cannulated and draining at three levels to vary outflow resistance (5 cm above, level with, or 20 cm below the SO). GB filling or emptying represented the algebraic difference between hepatic secretion (equal to the intravenous infusion rate) and rate of TCA delivery into the duodenum. With the sphincter intact the rate of bile acid delivery averaged one-half the intravenous infusion rate at 0-40% of the MMC cycle period, rose to exceed the intravenous infusion rate at 60-70% of the cycle period, and then fell to lower levels before the next MMC began. The pattern of delivery was identical with the SO cannulated, but the rate and percent infused TCA delivered into the duodenum depended significantly (P less than 0.01) on outflow resistance. They were least with the reservoir elevated 5 cm, intermediate when level, and greatest when 20 cm lower. Thus, duodenal bile acid delivery and GB filling or emptying during fasting were cyclically coordinated with the MMC. Peak rates of duodenal bile acid delivery and active GB emptying occur at 70% of the duodenal cycle period. Elimination of the SO does not eliminate the pulsatile pattern of fasting duodenal bile acid delivery, but outflow resistance determines the quantities delivered into the duodenum or stored in the GB. Thus, during the interdigestive period the net effect of SO function does not differ from a constant output resistance favoring the partition of hepatic biliary secretion into the GB and away from the duodenum, while the pulsatile pattern of duodenal bile acid delivery associated with the MMC results from cyclic active contraction of the GB.