Regulation of aldosterone synthase cytochrome P450 (CYP11B2) and 11β- hydroxylase cytochrome P450 (CYP11B1) expression in rat adrenal zona glomerulosa cells by low sodium diet and angiotensin II receptor antagonists

Changes in the mRNA levels for aldosterone synthase cytachrome P450 (CYP11B2 or P450(aldo)) and 11β hydroxylase cytochrome P450 (CYP11B1 or P450(11β)) in rat adrenal glands were studied in response to angiotensin II type 1 (AT1) and type 2 (AT2) receptor antagonists. CYP11B1 and CYP11B2 genes were highly homologous (88.5%) in their nucleotide sequences of the amino acid ceding regions. Reverse transcription-polymerase chain reactions (RT- PCR) which are capable of discriminating between rat CYP11B1 and CYP11B2, were performed with specific primers for each P450. Upon sodium restriction (5 mmol Na⁺/kg of diet) of rats for 14 d, the amount of the CYP11B2 mRNA in the adrenal glands was increased 8.5-fold compared to that from the rats fed a normal diet (225 mmol Na⁺/kg of diet) whereas no significant change in the CYP11B1 mRNA was observed after the dietary sodium restriction. As shown by an immunoblot analysis, the adrenal capsule portions (mainly zona glomerulosa) of the rats kept on the low Na diet for 14 d expressed significantly higher levels of both CYP11B2 and CYP11B1, and contained a significantly higher amount of CYP11B2 than those from the rats fed by normal diet. The activities of the CYP11B2 enzyme were also found to be increased by about 8-fold on day 14. In concert with these alterations, the plasma aldosterone concentration (PAC) increased. However, when the specific AT1 antagonist E4177 was given to rats maintained on the low Na diet, the amount and activity of CYP11B2, as well as the PAC, were suppressed. In contrast, the increase in CYP11B2 induced by the low Na diet was not affected by the AT2-specific antagonist PD123177. These results indicate that the aldosterone synthase cytochrome P450 (CYP11B2) is an ultimate target of the regulation of aldosterone biosynthesis by an AT1 receptor antagonist.