Plasma cholesterol levels in rabbits but not in rats increase tremendously after cholesterol feeding.In recent in vivo studies,we found that this is due to activation of FXR (famesoid X receptor) in cholesterol-fed rabbits but not in rats.The aim of the present study was to investigate why when FXR is activated,CYP7A 1 is down-regulated in spite of the fact that LXR (liver X receptor,another orphan nuclear receptor which up-regulates CYP7A 1) is simultaneously activated by dietary cholesterol.A 1.14 kb rabbit CYP7A1 5-flanking region (promoter) was cloned.The putative binding sites for FTF (fetoprotein transcription factor) and LXR were identified and were confirmed as being functional.