Objectives: Unlike Dahl salt-sensitive (SS) rats, some strains of spontaneously hypertensive (SHR) rats develop only minor organ damage even when exposed to high-salt diet. In previous linkage studies, we identified quantitative trait loci on rat chromosome 19 (RNO19) linked to the SHR allele suggesting a protective effect against salt-induced hypertensive organ damage in SS.
Methods: To test the relevance of this finding, we generated and characterized a consomic strain SS-19SHR in which RNO19 from SHR was introgressed into the susceptible background of SS. We compared the effects of low-salt (0.2% NaCl) and high-salt (4% NaCl) diet exposure for 8 weeks on the development of hypertension and target organ damage in male consomic and SS animals (n=14-20, each).
Results: Systolic blood pressure, relative left ventricular weight and urinary protein excretion were significantly lower in SS-19SHR compared to SS under both low-salt and high-salt diet (P < 0.05, respectively). Left ventricular atrial natriuretic peptide mRNA expression showed a more pronounced 4.5-fold increase in SS compared to SS-19 (two-fold) after high-salt (P < 0.05). In comparison to low diet, high-salt exposure induced a significant increase in vascular aortic hypertrophy index, left ventricular interstitial fibrosis (+210%) and perivascular fibrosis (+195%) in SS but not in consomic SS-19SHR (P < 0.05, respectively).
Conclusions: These results demonstrate a strong protective effect of RNO19 from SHR on the development of hypertension, salt-sensitivity, cardiovascular and renal organ damage in SS. In particular, we demonstrate a genetic effect protecting against the development of cardiac fibrosis in salt-sensitive hypertension.