Sex Differences in Blood Pressure and mRNA expression of Renal Sodium Transporters in Mice Under Normal Sodium Diet

Abstract

We previously reported sex differences in blood pressure and the renal handling of sodium in mice consuming high salt diet (Fan L., et al FASEB J. 30, 731.6, 2016). The purpose of this study was to determine sex differences in blood pressure and mRNA expression of key renal sodium transporters in mice consuming normal chow and water for six weeks. Four‐week old intact male and female CD‐1 mice were purchased from Harlan, Inc. (ENVIGO) (Indianapolis, IN). Female and male mice (n = 5/group) were placed in metabolic cages and consumed normal chow (Harlan Teklad 2019) and water ad libitum for six weeks. Blood pressure in these mice was measured 5 days/week via the tail‐cuff technique (Kent Scientific CODA device). Separate mice in bins were maintained on the same dietary regimen and used for mRNA analysis of renal sodium transporters. Four mice in each group were sacrificed at the end of the first, third, fifth, and sixth weeks. Kidneys were removed, total RNA was extracted from renal cortical tissue and measured for quantity and quality, and this was followed by first‐strand cDNA synthesis. Real time qt‐PCR was performed using Sybr green and the RT2 Profiler™ PCR Custom Array system from SABiosciences (QIAGEN). Arrays contain primers of the following renal transporters ENaC (a, b, g subunits), NKCC2, NCC, NHE2, NHE3, SGLT, Agtr1a, and Atp1a1. Mean blood pressure (MBP, mmHg) averaged weekly was analyzed via two‐way ANOVA with repeated measures. Real time data was determined via ΔΔCt method and analyzed via RT2 Profiler™ PCR Array Data Analysis (Version 3.5) by SABiosciences. Results indicated that female kidneys expressed significantly higher mRNA levels of ENaC (b), NCC, Agtr1a, NHE2, and NHE3 in all four measured periods, higher levels of ENaC (a & g) and SGLT in three of the four periods, and higher NKCC2 levels in one period. Most expression levels were 2 fold or higher in female kidneys. Males had significantly higher MBP than females in week two (82.3 ± 3.5 vs 69.5 ± 2.0, respectively, p < 0.02) and had non‐significantly higher MBP in all other weeks. Both sexes showed increased MBP from week one to week six (female: 72.3 ± 1.1 to 82.2 ± 1.7, p < 0.07; and male: 79.9 ± 3.2 to 88.6 ± 3.2, p < 0.05). We conclude that female mice express higher mRNA levels of renal sodium transporters than male mice and maintain lower MBP than male mice. We suggest that both estrogen and testosterone play important roles in the sex differences in mRNA expression and blood pressure.Support or Funding InformationResearch supported by Oklahoma INBRE 8P20GM103447 Summer Research Program.