Dahl Salt-Resistant Rat Is Protected against Hypertension during Diet-Induced Obesity

Abstract

A high-fat diet (HFD) frequently causes obesity-induced hypertension. Because Dahl salt-resistant rats are protected against hypertension after high-salt or high-fructose intake, it is of interest whether this model also protects against hypertension after diet-induced obesity. We tested the hypothesis that Dahl salt-resistant rat protects against hypertension during diet-induced obesity. Dahl salt-sensitive (SS) and Dahl salt-resistant (SR) rats were fed a HFD (60% fat) or a chow diet (CD; 8% fat) for 12 weeks. We measured blood pressure using the tail-cuff method. The paraffin sections of thoracic perivascular adipose tissue (tPVAT) were stained with hematoxylin/eosin and trichrome. The expression of genes in the tPVAT and kidneys were measured by reverse transcription-quantitative polymerase chain reaction. The HFD induced hypertension in SS (p < 0.01) but not SR rats, although it increased body weight gain (p < 0.05) and tPVAT weight (p < 0.01) in both rats. The HFD did not affect the expression of genes related to any of the adipocyte markers in both rats, although SR rats had reduced beige adipocyte marker Tmem26 levels (p < 0.01) and increased anti-inflammatory cytokine adiponectin (p < 0.05) as compared with SS rat. The HFD did not affect the mRNA expression of contractile factors in the tPVAT of SS and SR rats. SR rats are protected against hypertension during diet-induced obesity. This result implies that the genetic trait determining salt sensitivity may also determine fructose and fat sensitivity and that it is associated with the prevention of hypertension.

Keywords: Dahl salt-resistant rat; Dahl salt-sensitive rat; hypertension; obesity; perivascular adipose tissue.

Figure 1

The effects of a high-fat diet on systolic blood pressure (SBP), diastolic blood pressure (DBP), body weight, water intake, food intake, and calorie intake in Dahl salt-sensitive (SS) and salt-resistant (SR) rats. SS and SR rats were fed either a chow diet (CD, 8.6% fat) or a high-fat diet (HFD, 60% fat) for 12 weeks. (A) The HFD increased the SBP in SS rats but not in SR rats. (B) The HFD increased body weight gain in both the SS and SR rats. (C–E) Water intake, food intake, and calorie intake are shown. As food intake decreased in the HFD groups, there was no difference in calorie intake between the CD and HFD groups. Graph, mean ± SEM of 6 independent experiments. Two-way analysis of variance followed by Tukey’s post hoc multiple comparisons test. * p < 0.05 and ** p < 0.01 vs. the SS CD group. # p < 0.05 and ## p < 0.01 vs. the SR CD group. ○, SS-CD; ●, SS-HFD; △, SR-CD; ▲, SR-HFD.

Figure 2

The effects of a high-fat diet on fat deposits, weight, histological characteristics, and adipocyte area of the thoracic perivascular adipose tissues (tPVAT) in SS and SR rats. (A) Representative pictures visualizing tPVAT from the SS and SR rats fed a CD or HFD for 12 weeks. The HFD increased fat deposits (A) and PVAT weight (B) in both the SS and SR rats. (C,D) Representative microscopic images of the thoracic aortas and tPVAT from the SS and SR rats fed a CD or HFD for 12 weeks. The thoracic aortas and tPVAT sections were stained with hematoxylin and eosin (H&E, upper) and trichrome (lower) stains. The scale bars for 100×, 200×, and 400× magnification were 200, 100, and 50 μm, respectively. The HFD increased the PVAT adipocyte area (black arrow) in SS rats but not SR rats. Graph, mean ± SEM of 6 independent experiments. Two-way analysis of variance followed by Tukey’s post hoc multiple comparisons test. * p < 0.05 and ** p < 0.01 vs. the SS CD group. ## p < 0.01 vs. the SR CD group.

Figure 3

The effects of a high-fat diet on the expression of adipocyte marker genes in PVAT from SS and SR rats. The mRNA expression of brown adipocyte-related genes such as uncoupling protein 1 (Ucp1, A), peroxisome proliferator-activated receptor γ coactivator 1-α (Pgc-1α, B), and peroxisome proliferator-activated receptor γ (Pparγ, C), a beige adipocyte-related gene such as transmembrane protein 26 (Tmem26, D), and a white adipocyte-related gene such as Leptin (E) were measured by RT-qPCR in PVAT from SS and SR rats fed a CD or HFD for 12 weeks. Graph, mean ± SEM of 6 independent experiments. Two-way analysis of variance followed by Tukey’s post hoc multiple comparisons test. ** p < 0.01 vs. the SS CD group.

Figure 4

The effects of a high-fat diet on adipose tissue derived inflammatory factors in PVAT from SS and SR rats. Tissue levels of proinflammatory cytokines (interleukin-6 [IL-6, A] and tumor necrosis factor α [TNFα, B]) and an anti-inflammatory cytokine (adiponectin, C) were detected via enzyme-linked immunosorbent assay (ELISA) in SS and SR rats fed a CD or HFD for 12 weeks. Graph, mean ± SEM of 6 independent experiments. Two-way analysis of variance followed by Tukey’s post hoc multiple comparisons test. * p < 0.05 vs. the SS CD group.

Figure 5

The effects of a high-fat diet on the expression of genes related to contractile factors in PVAT from SS and SR rats. The mRNA expression of angiotensin II-related genes such as angiotensin-converting enzyme (Ace, A) and angiotensinogen (Agt, B), a norepinephrine-synthesizing gene such as tyrosine hydroxylase (C), chemerin-related genes such as rarres2 (D) and chemerin receptor 23 (Cmklr1, E), and a serotonin-related gene such as serotonin transporter (Slc6a4, F) were measured by RT-qPCR in PVAT from SS and SR rats fed a CD or HFD for 12 weeks. Graph, mean ± SEM of 6 independent experiments. Two-way analysis of variance followed by Tukey’s post hoc multiple comparisons test.

Figure 6

The effects of a high-fat diet on the expression of genes related to angiotensin II in kidneys from SS and SR rats. The mRNA expressions of angiotensin II-related genes such as Renin (A), Ace (B), Ace2 (C), Agt (D) were measured by RT-qPCR in the kidneys of SS and SR rats fed a CD or HFD for 12 weeks. Graph, mean ± SEM of 6 independent experiments. Two-way analysis of variance followed by Tukey’s post hoc multiple comparisons test.

Figure 7

The effects of a high-fat diet on the expression of genes related to angiotensin II receptor in kidney from SS and SR rats. The mRNA expression of angiotensin receptor related genes such as angiotensin II type 1a receptor (At1ar, A), angiotensin II type 1b receptor (At1br, B), angiotensin II type 2 receptor (At2r, C), and mas1 proto-oncogene (Mas1, D) were measured by RT-qPCR in kidney from SS and SR rats fed a CD or HFD for 12 weeks. Graph, mean ± SEM of 6 independent experiments. Two-way analysis of variance followed by Tukey’s post hoc multiple comparisons test.