Effect of dietary sodium on estrogen regulation of blood pressure in Dahl salt-sensitive rats

Abstract

The effects of high-sodium (HS) and normal-sodium (NS) diets on ovarian hormone modulation of mean arterial pressure (MAP) were examined in Dahl salt-resistant (DR) and salt-sensitive (DS) rats. Ovariectomy increased MAP (OVX-Sham) to a greater extent in DS rats maintained for 2 wk on a HS (22 mmHg) compared with a NS (6 mmHg) diet. Ovariectomy had no effect on MAP in DR rats on NS but did increase MAP in rats on HS (10 mmHg) diets. On HS diets, glomerular filtration rate (GFR) was 36% less in the DS-Sham than DR-Sham animals; ovariectomy increased GFR in both strains by 1.4–1.5-fold; glomerular angiotensin II type 1 receptor (AT1R) densities were 1.6-fold higher in the DS-Sham than in the DR-Sham group; ovariectomy increased glomerular AT1R densities by 1.3-fold in DR rats but had no effect in DS rats; 17β-estradiol (E2) downregulated adrenal AT1R densities in both strains on either diet; ovariectomy reduced estrogen receptor-α (ER-α) protein expression in the renal cortex by 40–50% although renal ER-α expression was 34% lower in DS than in DR rats. These observed effects of gonadectomy were prevented by E2treatment, suggesting that E2deficiency mediates the effects of ovariectomy on MAP, GFR, AT1R densities, and renal ER-α protein expression. In conclusion, ovariectomy-induced increases in MAP are augmented by HS diet in both strains, and this effect is not mediated by a reduction in GFR. Aberrant renal AT1R regulation and reduced renal ER-α expression are potential contributors to the hypertensive effects of E2deficiency in DS rats. These findings have implications for women with salt-sensitive hypertension and women who are E2deficient, such as postmenopausal women.