Potential Sex Differences in Blood Pressure and Sodium Excretion in Spironolactone‐Treated Mice Transitioning from a Normal Diet to a Salt‐Deficient Diet to a High‐Salt Diet

Abstract

Mineralocorticoid receptor (MR) antagonism is a therapeutic approach that has beneficial effects for patients with heart failure and renal disease. Recent reports of sex differences with respect to MR antagonism could eventually lead to differential treatment of men and women with hypertension and cardiovascular disease. The purpose of this study was to investigate sex differences in blood pressure and sodium excretion in mice treated with the MR antagonist spironolactone. Intact male and female CD-1 mice, 5 – 7 weeks old, were purchased from ENVIGO, Inc. Mice were placed in metabolic cages for a 5-day baseline (BL) period consuming normal food with water. After BL, either a placebo (P) or spironolactone (Sp) pellet (25mg, 21-day release, Innovative Research of America) was implanted sc and mice consumed a salt-deficient (SD) diet (Teklad, TD90228) with water for seven days. After the SD period, mice consumed a high-salt (HS) diet of 4% NaCl with 1% saline for seven days. Groups included male-P (MP), male-Sp (MSp), female-P (FP), and FSp (n=6/group). Systolic blood pressure (SBP, mmHg) was measured daily via the tail-cuff technique. Sodium balance was measured daily via sodium intake – sodium excretion, which was determined by urine volume × urine sodium concentration. In male mice, SBP decreased in the SD period in both MP & MSp mice: (BL vs SD: 105.0 ± 1.1 vs 100.8 ± 1.2 p<0.005; 108.7 ± 2.0 vs 102.5 ± 1.8, p<0.01 respectively). In MP mice, SBP increased in the HS period (107.2 ± 1.9, p<0.02 compared to SD) whereas in MSp mice SBP was not different (98.3 ± 3.7, p<0.08 compared to SD). In female mice, SBP was not different between BL and SD periods in either FP or FSp mice: (BL vs SD: 97.5 ± 1.7 vs 96.2 ± 1.1; 98.8 ± 1.8 vs 100.6 ± 1.4, respectively). As in the males, SBP increased in FP mice in the HS period (104.2 ± 2.3, p<0.02 vs SD), but did not change in FSp mice (100.6 ± 2.3). Sodium excretion was significantly higher in FSp compared to FP mice in both the SD and HS periods whereas sodium excretion was not significantly different between MP and MSp mice in both SD and HS periods. In summary, consuming the SD diet for seven days lowered SBP in male mice but not in female mice. In transitioning from the SD to HS diets, SBP increased in the untreated male and female mice but remained stable in spironolactone-treated male and female mice. We conclude MR antagonism prevents HS-induced elevation in blood pressure. MR is a ubiquitous transcription factor and thus potential sex differences regarding in not only renal sodium handling but also other physiological mechanisms related to blood pressure need further investigation.