Page 56 - Human Bile Acid Metabolism: a Postprandial Perspective

Chapter 3
As a consequence, plasma insulin concentrations in the hepatic vein and beyond were substantially lower than in the portal vein. The postprandial negative muscle flux indicates uptake of glucose by the muscle. The negative kidney glucose flux indicates uptake of glucose by the kidneys.
BAs continuously cycle in the enterohepatic circulation of pigs regardless
of food status
Total BA concentrations in the portal vein were at least 6 times higher than in the other blood vessels, reflecting that most BAs are contained within the enterohepatic cycle (fasted state total BA concentration in portal vein: 25.01 ± 2.8 mM and caval vein: 4.29 ± 1.0 mM, p < 0.0001). In addition, the baseline fluxof portal vein BAs indicates that BAs also circulate in the enterohepatic circulation in the postabsorptive state, while total BA concentrations between the hepatic, renal or caval veins and aorta were not different (Fig. 3B-E).
Postprandial BA concentrations rise with large variability between animals
After the meal, BA concentrations increased in the portal vein, and, to a much lesser extent, in the peripheral circulation, with a broad peak around 1.5-2 h after the meal (Fig. 3B-E). In contrast to the relatively uniform postprandial glucose and insulin responses, these postprandial BA responses revealed relatively large interanimal variabilities (Supplemental Figs. S5-9). When aligning the individual postprandial concentration curves at their peak a significant postprandial rise in BA concentration becomes apparent, for example for glycine-conjugated hyodeoxycholic acid (gHDCA) (Supplemental Fig. S10). The most prominent BAs present in the portal vein were glycine-conjugated (g) chenodeoxycholic acid (CDCA) and gHDCA, followed by their taurine-conjugated (t) and unconjugated forms (Fig. 3E,F). Conjugated and unconjugated forms of lithocholic acid (LCA) and ursodeoxycholic acid (UDCA) were well detected in the portal vein but their concentrations were very low elsewhere (Fig. 4).
Porcine hepatic clearance is most efficient for conjugated CDCA forms
The BA profile in the peripheral circulation was similar to the portal vein, albeit with much lower concentrations except for gCDCA (Figs. 3 and 4). Even though gCDCA and gHDCA were the most prominent BAs in the portal vein, hepatic vein concentrations of gCDCA were much lower than gHDCA concentrations (Fig. 3F; ratio gHDCA:gCDCA in P: 0.95 ± 0.1 vs in V: 3.04 ± 0.3; p < 0.0001).
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