The Cholesterol Side Chain Cleavage System of the Rat Adrenal Cortex and Its Relationship to the Circadian Rhythm*

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Abstract
The adrenal mitochondrial cytochrome P450 systems were examined at the low and high points of the circadian rhythm in female rats maintained on a light cycle from 0600–1800 h. The rate of association of cholesterol with the cholesterol side chain cleavage form of cytochrome P450 (P450scc) was measured by light absorption spectrometry. Cholesterol binding to P450scc was as high in rats killed at the beginning of the dark period as it was in stressed rats at the beginning of the light period. Stressing rats at the beginning of the dark period did not result in a further increase in the rate of cholesterol association with P450scc despite a further increase in serum corticosterone levels. This suggests that other reactions of cholesterol metabolism in the adrenal cortex are contributing in a significant way to the increased rate of corticosteroidogenesis seen in stressed animals.