Aerobic Swim Training Restores Aortic Endothelial Function by Decreasing Superoxide Levels in Spontaneously Hypertensive Rats

Abstract

Objective:: We aimed to determine whether aerobic training decreases superoxide levels, increases nitric oxide levels, and improves endothelium-dependent vasodilation in the aortas of spontaneously hypertensive rats.

Methods:: Spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) were distributed into 2 groups: sedentary (SHRsd and WKYsd, n=10 each) and swimming-trained (SHRtr, n=10 and WKYtr, n=10, respectively). The trained group participated in training sessions 5 days/week for 1 h/day with an additional work load of 4% of the animal's body weight. After a 10-week sedentary or aerobic training period, the rats were euthanized. The thoracic aortas were removed to evaluate the vasodilator response to acetylcholine (10-10 to 10-4 M) with or without preincubation with L-NG-nitro-L-arginine methyl ester hydrochloride (L-NAME; 10-4 M) in vitro. The aortic tissue was also used to assess the levels of the endothelial nitric oxide synthase and nicotinamide adenine dinucleotide oxidase subunit isoforms 1 and 4 proteins, as well as the superoxide and nitrite contents. Blood pressure was measured using a computerized tail-cuff system.

Results:: Aerobic training significantly increased the acetylcholine-induced maximum vasodilation observed in the SHRtr group compared with the SHRsd group (85.9±4.3 vs. 71.6±5.2%). Additionally, in the SHRtr group, superoxide levels were significantly decreased, nitric oxide bioavailability was improved, and the levels of the nicotinamide adenine dinucleotide oxidase subunit isoform 4 protein were decreased compared to the SHRsd group. Moreover, after training, the blood pressure of the SHRtr group decreased compared to the SHRsd group. Exercise training had no effect on the blood pressure of the WKYtr group.

Conclusions:: In SHR, aerobic swim training decreased vascular superoxide generation by nicotinamide adenine dinucleotide oxidase subunit isoform 4 and increased nitric oxide bioavailability, thereby improving endothelial function.

Figure 1

Hemodynamics and effort test variables pre- and post-aerobic training or the sedentary period. Peak oxygen uptake (A); HR (B); and MBP (C). *p<0.05; post-training compared with pre-training; #p<0.05; trained group after training compared with the sedentary group after training; and **p<0.01, SHR vs. WKY. The data are presented as the mean ± SEM.

Figure 2

Relative maximal endothelium-dependent vasorelaxation induced by ACh (A) and relative maximal endothelium-independent vasorelaxation following the SNP treatment (C). Curves showing the maximal endothelium-dependent vasorelaxation (ACh: 10^–10 to 10^–4 M) and maximal endothelium-independent vasorelaxation (SNP: 10^–12 to 10^–4 M) (B and D, respectively) of the aortas of control WKY (circles) and SHR (square). *p<0.01 and **p<0.001 SHRsd group compared with the WKYsd, WKYtr and SHRtr groups. The data are presented as the mean ± SEM.

Figure 3

Relative maximal endothelium-dependent vasorelaxation induced by ACh (A) and curves of the maximal endothelium-dependent vasorelaxation (ACh: 10^–10 to 10^–4 M) of the aortas of control WKY (circles) and SHR (square) (B) after a 30-min preincubation with an inhibitor of NO synthesis (L-NAME; 10^-4 M). *p<0.05 and **p<0.01 SHRsd compared with WKY. The data are presented as the mean ± SEM.

Figure 4

Densitometry analysis of the levels of the eNOS, *p=0.002 SHRsd group compared with WKY (A); Nox4, *p=0.001 SHR compared with WKY and #p=0.02 SHRtr group compared with the SHRsd group (B); and Nox1 proteins (C). Representative blots (D) of samples of the aortas from the WKYsd, WKYtr, SHRsd and SHRtr groups. The data are presented as the mean ± SEM.

Figure 5

Quantitative analysis of the superoxide content, *p=0.01 SHRsd group compared with the SHRtr, WKYtr and WKYsd groups (A); representative fluorescence micrographs of confocal microscopy images (B) and vascular nitrite levels *p=0.002 SHRsd compared with the SHRtr, WKYsd and WKYtr groups (C) in samples of the aortas from the WKYsd, WKYtr, SHRsd and SHRtr groups. The data are presented as the mean ± SEM.