Summary: Cortisol is responsible for the recycling of bile acids from the blood, according to new research. If this recycling is disrupted, the animals develop gallstones and lose weight because they are no longer able to digest dietary fats. They also use more energy for heat production. The researchers assume that regulation of recycling serves the purpose of conserving energy efficiently in times of need. Nature sees to it that we do not have "too much choler" (bile) in our body. A delicately equilibrated regulation system ensures that there is always exactly the right amount of bile in the gallbladder. When we are hungry, our body releases a hormone called cortisol, which is a glucocorticoid. Hepatic cells receive this hormone signal through their cortisol receptors (glucocorticoid receptors) and respond by filling the gallbladder with bile in preparation of the imminent food intake. Directly upon eating a meal, bile is secreted into the intestine.
Bile acids contained in bile are indispensable for fat digestion. They emulsify fats into minute droplets, which can be broken down. Our body recovers 95 percent of bile acids from the bowel contents. They are reabsorbed by cells of the intestinal mucosa and transported back to the liver via the blood.
"We have now found out that this recycling process is controlled by the cortisol hormone," says Dr. Stephan Herzig. Herzig is head of the Division of Molecular Metabolic Control - a joint research department of the German Cancer Research Center (DKFZ), the Center for Molecular Biology (ZMBH) of Heidelberg University, and Heidelberg University Hospitals. The research group has published its results in the journal Cell Metabolism. To obtain proof of cortisol's key role in bile acid recycling, the investigators used mice whose hepatic cells specifically lack the cortisol receptor. That means that cortisol signals are not received in the liver. When the modified animals were hungry, their bile contained considerably less bile acid than that of normal animals. This also led to a reduced solubility of cholesterol in the gallbladder so that an increased amount of gallstones developed. Compared to animals with intact cortisol receptor, the genetically modified mice lost weight, because they excreted fats contained in the food without digesting or using them.