The gut, not the liver, is the main control center that tells the liver when to stop making bile acids — when bile acids enter gut cells, they trigger a signal (FGF15) that shuts down bile acid...

When mice can’t send bile acids out of their gut cells, the bile acids pile up inside the cells, tricking the body into thinking there’s too much bile acid overall — so the liver stops making more, even though the total amount in the body actually goes down.