Normotension in Lewis and Dahl salt-resistant rats is governed by different genes.

Objectives: Inbred rodent models simulating essential hypertension and normotension are useful tools in discovering genes controlling blood pressure (BP) homeostasis. An analysis of a F2 population made from crosses of hypertensive Dahl salt-sensitive (DSS) and normotensive Lewis rats did not detect a BP quantitative trait locus (QTL) on chromosome 7 (Chr 7). However, false negativity could not be excluded. If a BP QTL could be proven to exist, what gene(s) may be responsible for this QTL.

Methods: We first constructed reciprocal congenic strains for a Chr 7 segment and determined functional domains of prominent candidate genes.

Results: A congenic strain made in the DSS rat background exhibited a BP effect, indicating that a BP QTL, C7QTL, inhabits Chr 7. Contrarily, a congenic strain constructed in the Lewis rat background did not change BP, demonstrating a dependence of C7QTL on the DSS rats environment. Among the candidate genes, tachykinin 2 (Tac2), neurexophilin 4 (Nxph4) and retinol dehydrogenase 2 (Rdh2) bear nonsynonymous changes comparing DSS and Lewis rats, but are the same comparing DSS and Dahl salt-resistant (DSR) rats. In contrast, the Lewis alleles of 11-beta-hydroxylase (Cyp11b1), aldosterone synthase (Cyp11b2) and Cytochrome P-450 11B3 (Cyp11b3) are identical to those of DSS rats, but different from those of DSR rats.

Conclusion: Thus, the failure to detect a linkage between a Chr 7 segment and BP in F2(DSS × Lewis) can be attributed to false negativity. Tac2, Nxph4 and Rdh2 are priority candidate genes for C7QTL. Lewis and DSR rats are both normotensive, but their underlying genetic determinants are different.