Relationships between circadian cycles of rat adrenal cholesterol ester metabolizing enzymes, cholesterol, ascorbic acid, and corticosteroid secretion.

The circadian changes in rat adrenal cholesterol ester (CE) metabolism have been studied and related to the circadian changes in adrenal ascorbic acid and corticosterone levels and plasma corticosterone levels. Significant declines in the ratio of CE/C, cholesterol esterase (CEase) and acyl CoA:cholesterol acyl transferase (ACAT) activities occur during the peak and declining phases of adrenal and plasma corticosteroids, suggesting that when there is a decreased need for steroid precursors the amount of stored CE is decreased, and that the enzymes involved in CE metabolism decline in activity. Adrenal ascorbic acid has a biphasic rhythm with peaks at 0900 and 2200 h. The rhythm of ascorbic acid appears to be inverse to that of ACAT activity, suggesting possible relationships between the two parameters.