Coordinate diurnal regulation of hepatic acyl-coenzyme A: cholesterol acyltransferase and cellular levels of esterified cholesterol.
Hepatic ACAT, HMG-CoA reductase and both cellular free and esterified cholesterol were measured at 3 h intervals over a 24 h period in the rat. ACAT exhibited a characteristic low amplitude diurnal rhythm with maximum activity at the mid-light phase that was significantly higher than the minimum activity observed at the mid-dark phase. The cellular esterified cholesterol concentration showed a diurnal rhythm that closely paralleled the rhythm of ACAT activity. The cellular free cholesterol concentration was not significantly altered during the 24 h cycle. In rats fed cholesterol, the diurnal rhythm of ACAT was still maintained despite the increase in ACAT activity during the entire 24 h cycle suggesting that the ACAT rhythm is the result of changes in the level of ACAT protein expression. The results also indicate that the diurnal rhythms of ACAT and HMG-CoA reductase are generated by a process independent of the LDL receptor rhythm. All three rhythms are also independent of changes in the level of free cholesterol in the cell.
Szanto
A
A
Lipid Department, University of New South Wales, School of Medicine, St. Vincent's Hospital, Darlinghurst, Australia.
Ruys
J
J
Balasubramaniam
S
S
D000818:Animals; D002784:Cholesterol / Q000378:metabolism / Q000494:pharmacology; D002788:Cholesterol Esters / Q000378:metabolism*; D002940:Circadian Rhythm; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar
D002788:Cholesterol Esters; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases