We studied the effect of alterations in the intake of sodium and potassium as well as changes in circulating adrenocorticotropin (ACTH) on the expression of the two rate-limiting systems of aldosterone formation in the rat. Low sodium and high potassium intake promoted time-dependent increases in the zona glomerulosa cytochrome P450scc (P450scc) and cytochrome P450c11 (P450c11) protein and mRNA levels, but no changes were found in the zona fasciculata-reticularis. In addition, these responses were associated with markedly elevated transcriptional activities. To further define the contribution of P450c11 and P450c18 (aldosterone synthase) in response to these differing intakes, we evaluated their mRNA levels using gene-specific oligonucleotide probes. P450c18 mRNA was restricted to the zona glomerulosa, whereas P450c11 mRNA was detected in both zona glomerulosa and zona fasciculata-reticularis. Furthermore, only P450c18 mRNA was induced by both low sodium or high potassium intake, as P450c11 mRNA levels remained unchanged. Captopril, an inhibitor of angiotensin-I converting enzyme, abolished the enhancing effects of the low sodium regimen on P450scc and P450c18 mRNA levels. Captopril also suppressed the augmentation of P450c18 mRNA observed with potassium supplementation but had no effect on P450scc mRNA levels. When the hypocholesterolemic drug 4-aminopyrazolopyrimidine (4-APP) was administered to rats for 3 consecurive days, both the level of plasma ACTH and the adrenal content of mRNA encoding P450scc increased 24 h post final injection. The coadministration of dexamethasone with 4-APP prevented these increases. In contrast, the mRNA content of P450c11 remained at control levels. In conclusion, this work demonstrates that variations in the intake of sodium and potassium act on the expression of the CYP11B2 gene, but not on that of the CYP11B1 gene. Moreover angiotensin-II (A-II) is an important factor in this mechanism of action. Both ions also enhance the expression of the CYP11A1 gene. A-II appears to participate in the mechanism of action of the low sodium intake at this level. Another mechanism is postulated for the action of potassium supplementation since captopril did not prevent the increased expression of the CYP11A1 gene. In addition, the fact that 4-APP enhanced the mRNA level of P450scc but not that of P450c, also demonstrates different regulation of the P450s involved at the early and final steps of aldosteroone formation in the rat adrenal zona glomerulosa in vivo.
Copyright © 1992. Published by Elsevier Ltd.