Dahl's salt-resistant normotensive rat has mutations in cytochrome P450(11 beta), but the salt-sensitive hypertensive rat does not.

Molecular cloning of cytochrome P450(11 beta) cDNAs from the adrenal glands of Dahl's salt-sensitive hypertensive (DS) and salt-resistant normotensive (DR) rats was performed using a combined technique of the first strand cDNA synthesis by reverse transcriptase followed by polymerase chain reaction. The cDNA sequence of P450(11 beta)-DS was identical to that of wild type P450(11 beta). In contrast, the clone obtained from the DR rat contained six nucleotide substitutions causing five amino acid alterations (Arg-127-->Cys, Val-351-->Ala, Val-381-->Leu, Ile-384-->Leu, and Val-443-->Met). When the two cDNAs were expressed in COS-7 cells and steroid conversion rates of the transformed cells were determined, a ratio of 18-hydroxylation to 11 beta-hydroxylation of 11-deoxycorticosterone by P450(11 beta)-DS-expressed cells was 0.58, whereas that by P450(11 beta)-DR-expressed cells was 0.23. Plasma levels of 18-hydroxy-11-deoxycorticosterone and corticosterone (the 11 beta-hydroxylation product of 11-deoxycorticosterone) in DS and DR rats well reflected the steroidogenic activities of the two P450s. These results suggest that the characteristic plasma steroid level of the DR rat is caused by the mutations in P450(11 beta) gene and may act to maintain the normotensive blood pressure in this rat strain during sodium loading.