Lack of Suppression of Aldosterone Production Leads to Salt-Sensitive Hypertension in Female but Not Male Balb/C Mice

Abstract

Clinical studies indicate that salt-sensitive hypertension is more prevalent in women than in men. However, animal models of salt sensitivity have primarily focused on the mechanisms of salt sensitivity in male animals; therefore, elucidation of these mechanisms in female animal models is needed. We have previously shown that female Balb/C mice have higher aldosterone synthase expression and aldosterone production than males. We hypothesized that female Balb/C mice develop salt-sensitive increases in blood pressure. Seven-day feeding of a 4% NaCl high-salt (HS) diet increased blood pressure in female mice without altering blood pressure in males. Females on an HS diet displayed no apparent increases in sodium retention as assessed by 24-hour urine collection, sodium balance measure, and saline loading excretion analysis. Females on an HS diet exhibited lower renin-angiotensin system activity (plasma Ang II [angiotensin II], plasma renin activity, and ACE [angiotensin-converting enzyme] activity) compared with males but developed a salt-induced elevation in adrenal aldosterone synthase expression and retained higher aldosterone levels than males on HS. This resulted in a higher aldosterone/plasma renin activity ratio in females compared with males on HS feeding. Adrenal mRNA expression of angiotensinogen and leptin receptor was increased in female mice on an HS diet. HS impaired endothelium-dependent relaxation in female mice only. MR (mineralocorticoid receptor) inhibition (eplerenone) restored blood pressure and endothelial function in females on an HS diet. Collectively, these data indicate that Balb/C mice develop sex-discrepant salt-sensitive hypertension likely via aldosterone-MR-mediated mechanisms involving impaired endothelium-dependent relaxation in females only. This study presents the first model of spontaneous sex-specific salt sensitivity, which mimics the human pathology.

Keywords: adrenal cortex; aldosterone; endothelium; hypertension; mouse, Balb C; renin-angiotensin system; sex characteristics.

Figure 1.. High Salt Diet Increases Blood Pressure in Female Mice Only.

Average day (6:00–18:00) and night (18:00–6:00) blood pressure values over 7 days in male and female mice on NS and HS diets measured as mean arterial pressure (MAP) (A–B) systolic blood pressure (SBP) (C–D) and diastolic blood pressure (DBP) (E–F). *P<0.05. N=5.

Figure 2.. High Salt Diet Does Not Induce Salt retention in Female Mice.

(A) Urinary sodium and (B) potassium excretion and (C) urinary sodium/potassium ratio in male and female mice on NS and HS diets. (D) Plasma sodium in male and female mice on NS, HS and HS+Eplerenone. (E) Sodium excretion per day expressed as a percentage of measured sodium intake per day in metabolic cage collection (24 hours) in male and female mice on gel diets: NS, HS and HS+Eplerenone. *P<0.05. N=6.

Figure 3.. High Salt Diet suppresses Aldosterone Level in Male, but not Female, Mice.

Plasma levels of (A) angiotensin II (ANGII), (B) plasma renin activity (PRA), (C) angiotensin converting enzyme (ACE) activity, (D) aldosterone, (E) aldosterone/plasma renin activity ratio. (F) Western-Blot quantification and representative image for CYP11B2 expression in male and female mice on NS, HS and HS+Eplerenone. *P<0.05. N=4 for mass spectrometry measurements, N=7–18 for aldosterone ELISA, N=5–6 for western blotting.

Figure 4.. High Salt Diet Increases Adrenal Angiotensinogen and Leptin Receptor Expression in Female Mice.

Adrenal mRNA expression of (A) renin, (B) angiotensinogen and (C) leptin receptor in male and female mice on NS, HS or HS+Eplerenone. *P<0.05. N=3.

Figure 5.. Mineralocorticoid Receptor Blockade Restores Blood Pressure in Female Mice on a High Salt Diet.

Blood pressure in male and female mice on HSD and HSD+eplerenone. Average day and night (12 hours each) blood pressures over 7 days in male and female mice on HS and HS+eplerenone (EPL) measured as (A–B) mean arterial pressure (MAP), (C–D) systolic blood pressure (SBP) and (E–F) diastolic blood pressure (DBP). *P<0.05. N=4-10.

Figure 6.. High Salt Diet Impairs Endothelial Function in Female Mice Which Is Restored by Eplerenone Treatment.

Vascular reactivity in male and female mice on NS, HS and HS+eplerenone (EPL). Aortic ring relaxation responses to acetylcholine (ACH) (endothelium-dependent relaxation) in male (A) and female (B) mice on NS and HS and (C) male and (D) female mice on HS and HS+EPL expressed as a percentage of preconstriction with serotonin. *P<0.05 vs Female NS, N=5-10.