Ampicillin inhibits biliary cholesterol secretion.

There are compounds, other than bile salts, which influence biliary lipid composition. For example, the organic anions, bilirubin, and BSP, are secreted into bile and depress biliary phospholipid and cholesterol secretion. Ampicillin is also secreted into bile, but its effects on biliary lipid secretion are unknown. Therefore we measured biliary lipid secretion before, during, and after an ampicillin infusion. We infused bile salt pool depleted rats with a constant infusion of taurocholate. After biliary lipid secretion reached a steady state, the ampicillin solution was infused in a stepwise fashion. Within minutes after starting the ampicillin, bile flow and biliary ampicillin secretion increased. Simultaneously, biliary phospholipid and cholesterol, but not bile salt, secretion decreased significantly. The calculated lithogenic index of bile decreased significantly as well. Despite doubling the ampicillin infusion, neither biliary ampicillin, phospholipid, nor cholesterol secretion changed. After discontinuation of the ampicillin, bile flow and biliary ampicillin secretion decreased, while phospholipid and cholesterol secretion returned to normal. Ampicillin dramatically influences biliary lipid composition directly. It inhibits the biliary secretion of phospholipid and cholesterol, but not bile salt, and consequently reduces the molar percentage of cholesterol in bile.