Adrenal mitochondrial cytochrome P 450 and cholesterol side chain cleavage activity. Differences in the response of the zona glomerulosa and zona fasciculata reticularis to adrenocorticotropic hormone and its withdrawal

A comparison of the effects of adrenocorticotropic hormone (ACTH) on the cholesterol side chain cleavage system of zona glomerulosa and zona fasciculata reticularis tissue of the rat adrenal is presented. Following hypophysectomy, the rate of pregnenolone formation from endogenous cholesterol in mitochondria from zona fasciculata reticularis was lower than in mitochondria from zona glomerulosa. Also, the proportion of high spin, cholesterol bound side chain cleavage cytochrome P 450 was smaller, as measured by spectrophotometry and electron paramagnetic resonance spectroscopy. Treatment with ACTH brought about an increase in the rate of cholesterol side chain cleavage and in the proportion of high spin, cholesterol bound side chain cleavage cytochrome P 450 in mitochondria isolated from both zones. However, the percentage increase found in the zona fasciculata reticularis was much greater than in the zona glomerulosa. It is concluded that although both zones are affected by ACTH, the cholesterol side chain cleavage system of the zona fasciculata reticularis is much more sensitive than that of the zona glomerulosa to this hormone.