Intestinal cellular communication involving the farnesoid X receptor (FXR) and fibroblast growth factor 19 (FGF19) secretion regulates bile acid (BA) balance. Pigs born by cesarean surgery at 10 days preterm or near full-term were equipped with orogastric and umbilical arterial catheters. Pigs were administered a combination of parenteral nutrition and limited enteral nutrition for 5 days, then milk formula until the 26th day. At days 0, 5, 11, and 26, plasma and tissue samples were obtained. FGF19 levels in plasma, as well as FGF19 and other FXR target gene expression in the liver and distal intestine, were measured. Plasma FGF19 levels were lower in preterm newborn pigs compared to term newborn pigs, rose significantly by 5 days, particularly in preterm pigs, and thereafter declined in both groups until day 26. Similarly, intestinal FXR and FGF19 expression were lower in preterm newborn pigs compared to term newborn pigs, and it declined between days 5 and 26. In both groups, hepatic production of cholesterol 7-hydroxylase was inversely linked to plasma FGF19.
They conclude that the activity of the FXR-FGF19 axis is lower in preterm newborn pigs than in term newborn pigs, but rises transiently and subsequently falls by the first month of life. They also offer evidence for a negative feedback loop between plasma FGF19 and hepatic CYP7A1 expression.