Bile stimulants eg. Coptis

How do bile stimulants for eg.Coptis work? Does it cause the gall bladder to release more bile when taken or does it cause the liver to send more bile to the gallbladder so that there is more to release when fat is ingested. When does one take the Coptis, before eating, during or after? Is it the bitter taste of bile stimulants that stimulates the bile or is there some other method of action?

Thanks