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It is now known that in the rat there are two distinct species of cytochrome P45011β/18, namely aldosterone synthase and 11β-hydroxylase. Whereas aldosterone synthase is located exclusively in the zona glomerulosa, the zonal distribution and site of production of 11 β-hydroxylase is not entirely clear. In the present study we examined the zonal expression of 11β-hydroxylase mRNA in adrenals from control rats and animals subjected to ACTH treatment and dietary sodium restriction using a non-isotopic in-situ hybridization technique. The results were compared with those obtained using an inner zone specific antigenic (IZAg) marker to give unequivocal identification of the adrenocortical cell types.
11 β-Hydroxylase mRNA was clearly shown to be expressed in the inner zones of the control rat adrenal cortex, and none was detected in the zona glomerulosa and medulla. The message was more abundant in the outer zona fasciculata. A similar pattern of distribution of 11β-hydroxylase mRNA was observed in adrenals from rats subjected to dietary sodium restriction, although the width of the negatively staining layer of zona glomerulosa was significantly increased. In rats treated with 100 µg ACTH for 1 day, the number of cells expressing 11β-hydroxylase mRNA was increased, especially in the zona reticularis. With continued ACTH treatment, 11β-hydroxylase mRNA was found in the region of the zona glomerulosa, and after 3 and 5 days of ACTH treatment cells expressing 11β-hydroxylase mRNA extended to the connective tissue capsule. At this time there was a significant reduction in the total expression of the message compared with the controls.
These results suggest that the presence of 11β-hydroxylase in the zona glomerulosa cells is not essential for the late pathway for aldosterone biosynthesis from deoxycorticosterone. Like IZAg, the distribution of 11β-hydroxylase mRNA after prolonged ACTH treatment provides further evidence to support the hypothesis that ACTH increases the conversion of zona glomerulosa to zona fasciculata-like cells.
Journal of Endocrinology (1993) 139, 301–306
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