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 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 are 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 (BP). Seven day feeding of a 4% NaCl high-salt diet (HSD) increased BP in female mice without altering BP in males. Females on a HSD displayed no apparent increases in sodium retention as assessed by 24-hour urine collection, sodium balance measure and saline loading excretion analysis. Females on HSD exhibited lower renin-angiotensin system activity (plasma angiotensin II, plasma renin activity and angiotensin converting enzyme activity) compared to males but developed a salt-induced elevation in adrenal aldosterone synthase expression and retained higher aldosterone levels than males on high-salt. This resulted in a higher aldosterone/plasma renin activity ratio in females compared to males on high-salt feeding. Adrenal mRNA expression of angiotensinogen and leptin receptor were increased in female mice on HSD. HSD impaired endothelium-dependent relaxation in female mice only. Mineralocorticoid receptor inhibition (eplerenone) restored BP and endothelial function in HSD females. Collectively, these data indicate that Balb/C mice develop sex-discrepant salt-sensitive hypertension likely via aldosterone-mineralocorticoid receptor-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.

Gut Microbiota-Related Evidence Provides New Insights Into the Association Between Activating Transcription Factor 4 and Development of Salt-Induced Hypertension in Mice

“…Moreover, Bier et al (2018) demonstrated a significant association between gut microbiota composition and blood pressure regulation; even the metabolic short-chain fatty acids (SCFAs) may highlight another aspect of the complex interaction between diet, gut, and blood pressure. Additionally, it has been suggested that gut microbiota composition and microbial metabolites are the potential mediators between a single gene associated with blood pressure regulation and hypertension (Faulkner et al, 2018;Waghulde et al, 2018;Yang et al, 2018). In the present study, we found that ATF4 could regulate the gut microbiota composition and the expression of VK2 in hypersensitive mice induced by high-salt diet, suggesting that the mechanisms of ATF4 involved in blood pressure regulation and the vascular endothelial function may be related to gut microbiota and VK2.…”

Selective deletion of endothelial mineralocorticoid receptor protects from vascular dysfunction in sodium-restricted female mice

“…Excised thoracic aortas were cleaned of adipose tissue, cut in 2 mm rings, and mounted on DMT® wire myograph (Ann Arbor, MI). Concentration-response curves to phenylephrine, serotonin, sodium nitroprusside, and acetylcholine in the presence or absence of the nitric oxide synthase (NOS) inhibitor Nω-Nitro-L-arginine methyl ester hydrochloride (LNAME, 100 μM, 20 min preincubation) as well as maximum responses to KCl were performed and recorded with the LabChart® analysis software (AD Instruments®, Colorado Springs, CO) as previously described (1 nM-30 μm concentrations) [ 7 , 13 , 15 , 16 ].…”

“…Proteins were transferred to nitrocellulose membranes and stained for CYP11B2 (aldosterone synthase, antibodies generously supplied by Drs. Elise and Celso Gomez-Sanchez, University of Mississippi Medical Center) and β-actin as previously described [ 7 , 13 ]. In addition, RNA was isolated (Qiagen® minikit, Germantown, MD) from homogenates in Trizol (ThermoFisher®, Waltham, MA) followed by reverse transcription to obtain cDNA (ThermoFisher®, Waltham, MA).…”

“…qRT-PCR was performed utilizing Sybr Green (Applied Biosystems®, Foster City, CA) and the primer sequences in Table 1 . Ct values from each sample were normalized to 18 s expression within the sample (ΔCt) followed by normalization to control groups (ΔΔCt) prior to calculation of relative gene expression (2 −ΔΔCt ) as previously described [ 7 , 13 ] and in accordance with Applied Biosystems guidelines (Applied Biosystems® User Bulletin, no. 2, 1997).…”

“…In addition to an increased proclivity for endothelial MR expression, clinical and experimental data demonstrate that production of aldosterone is higher in females in response to pathological stimuli [ 10 – 12 ]. In a previous report, we demonstrated that inappropriately high aldosterone levels in salt-sensitive hypertensive female mice were associated with an increased expression of adrenal aldosterone synthase, the rate-limiting enzyme of aldosterone secretion (referred to as CYP11B2 , the encoding gene whose nomenclature is commonly used interchangeably), as well as dysregulation of the localized adrenal renin-angiotensin system [ 13 ]. These data indicate that the sex-specific clinical benefits of MR antagonists on cardiovascular health in women are attributable to a 2-pronged sex difference of heightened ECMR expression and aldosterone production in women.…”