REGULATION OF ALDOSTERONE SYNTHASE CYTOCHROME-P450 (CYP11B2) AND 11-BETA-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 cytochrome P450 (C YP11B2 or P450(aldo)) and 11 beta hydroxylase cytochrome P450 (CYP11B1 or P450(11 beta)) in rat adrenal glands were studied in response to a ngiotensin II type 1 (AT1) and type 2 (AT2) receptor antagonist. CYP11 B1 and CYP11B2 genes were highly homologous (88.5%) in their nucleotid e sequences of the amino acid coding regions. Reverse transcription-po lymerase 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 14d, the amount of the CYP11B2 mRNA in the adrenal glands was inc reased 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 mRN A was observed after the dietary sodium restriction. As shown by an im munoblot analysis, the adrenal capsule portions (mainly zona glomerulo sa) of the rats kept on the low Na diet for 14d expressed significantl y higher levels of both CYP11B2 and CYP11B1, and contained a significa ntly higher amount of CYP11B2 than those from the rats fed by normal d iet. The activities of the CYP11B2 enzyme were also found to be increa sed by about 8-fold on day 14. In concert with these alterations, the plasma aldosterone concentration (PAC) increased. However, when the sp ecific 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 su ppressed. In contrast, the increase in CYP11B2 induced by the low Na d iet was not affected by the AT2-specific antagonist PD123177. These re sults indicate that the aldosterone synthase cytochrome P450 (CYP11B2) is an ultimate target of the regulation of aldosterone biosynthesis b y an AT1 receptor antagonist.