Abstract
The primary bile acids (cholate and chenodeoxycholate) are synthesised from cholesterol in the liver with the enzyme cholesterol 7α-hydroxylase (CYP7A) being the rate-limiting step in the classic pathway. The activity of this enzyme has been known for some time to be under inhibitory feed-back control by bile acids.4 In view of the importance of this pathway in the removal of cholesterol, the mechanisms for the positive and negative regulation of transcription of the CYP7A gene have been studied.5 Until now, the mediator of the effects of bile acids had not been found.