Estrogen Does Not Protect Ovariectomized (OVX) Mice from Increased Blood Pressure and Sodium Retention Induced by High Fructose and High Salt (HF+HS) Diet

A preliminary study demonstrated that a HF+HS diet increased mean blood pressure (MBP) in intact female and male CD‐1 mice and this occurred earlier in female mice. Moreover, female mice showed higher sodium retention on HS+HF diet. To determine if estrogen plays a role in these HF+HS‐induced effects, we measured MBP, sodium retention, and mRNA expression of renal sodium transport mediators in OVX mice supplemented with either placebo (OP) or estrogen (OE) pellets (0.05mg, Innovative Research of America). Mice were purchased from Harlan, Inc., ovariectomized at 4.5 weeks of age, and implanted with pellets at 6 weeks of age. Three days after implantation, mice (n=6/group) were placed in metabolic cages and consumed normal diet and water for 4 days followed by 30 days of HF+HS diet consisting of 4% salt chow with a drinking solution of 20% fructose and 1% salt. Mice consumed normal diet and water for the recovery period of two weeks. Blood pressure was measured 5 days/week via tail‐cuff and sodium balance data were collected 4 days/week. Separate OE & OP mice on the same dietary protocol were sacrificed for bloodwork and RNA expression, via real‐time PCR, of renal‐cortical sodium transporters in the control period and every two weeks thereafter (n=4/group for each sacrifice). Results showed that baseline MBP (mmHg) tended to be higher in OE compared to OP mice (82.3±3.3 vs 72.9 ±2.1, respectively, p=0.08). After four weeks on the HF+HS diet, MBP in OE and OP mice was higher than baseline values (95.2±5.2 vs. 82.3±3.3, p<0.001, and 88.3±4.1 vs. 72.9±2.1, p<0.0001, respectively). After two weeks of recovery, MBP still exceeded baseline values in both OE and OP groups (89.2±5.3, p<0.05, and 82.7±3.6, p<0.01, respectively). The range of sodium retention (sodium intake – sodium excretion, μEq) averaged weekly was higher on HF+HS compared to baseline levels in OE and OP mice (48.6–60.6 vs. 5.4 p<0.001, and 36.4–55.2 vs. 4.7, p<0.001, respectively). OE mice retained 1.34 fold higher sodium than OP mice on weeks 2 and 4 of HF+HS diet (p<0.05) although total sodium retention in 4 weeks of HF+HS consumption was not significantly different between OE and OP (1547±118 vs 1285±77, respectively). Compared to baseline, HF+HS diet yielded higher renal mRNA expression of Agtr1a, Atp1a1, ENaC‐β, NCC, Slc34a1, NHE2, NHE3 in OP mice, and of Atp1a1, ENaC‐α, β, & γ, NCC, and Slc34a1 in OE mice. No expression differences occurred between the two groups. Plasma [Na + ] increased after two weeks on HF+HS diet in both groups but returned to baseline values on week 4. Kidney weight ‐to‐body weight (KW/BW) varied differently between OE and OP groups in that KW/BW decreased with HF+HS diet in OP mice whereas it increased in OE mice. We conclude that HF+HS diet increased MBP and sodium retention in OVX mice and estrogen supplementation provided no protection against these effects. Estrogen may even enhance sodium retention and exacerbate the effect on MBP. HF+HS diet‐induced increase in mRNA expression of specific renal sodium transporters may contribute to elevated MBP in HF+HS condition. Support or Funding Information Study supported by Oklahoma INBRE 8P20GM103447 Summer Research Program.