tokens: For this purpose , bile salt pool composition , synthesis of individual BS in vivo , hepatic activities , and expression levels of cholesterol 7alpha - hydroxylase ( CYP7A ) , and sterol 27 - hydroxylase ( CYP27 ) , as well as of other enzymes involved in BS synthesis , were analyzed in rats treated with EE ( 5 mg / kg , 3 days ) or its vehicle .