| Objective The present study was to determeine the effects of exercise training on arterial baroreflex and central oxidative stress in normotensive and spontaneously hypertensive rats (SHR) and to investigate the mechanisms by which exercise training improves baroreflex function in SHR.Methods 20 male 16-week-old SHR and 24 aged- and gender-matched Wistar rats were assigned randomly into four groups: sendentary normotensive Wistar rats (Wistar+Sed, n= 12), exercise-trained Wistar rats (Wistar+ExT, n= 12), sendentary hypertensive rats (SHR+Sed, n= 10) and exercise-trained hypertensive rats (SHR+ExT, n= 10). Rats run on a treadmill with low intensity for 8 to 9 weeks. Twenty-four hours after the end of ExT, arterial baroreflex were assessed by intravenous injection of phenylephrine (PE, 6μg/ kg) and sodium nitroprusside (NP, 6μg/ kg) in 4 groups of anesthetized rats. Baroreflex sensitivity (BRS) was calculated by change in heart rate in response to changes in blood pressure.The effects of intracerebroventricular infusion of Tempol and DETC on the BRS were determined. The total antioxidant capacity, malondialdehyde (MDA), enzyme activity of superoxide dismutase (SOD) and catalase were measured in the hypothalamus. The protein expression of Copper/Zinc-SOD (CuZn-SOD) and manganese SOD (Mn-SOD) in the hypothalmic paraventricular nucleus (PVN) was assessed by western blotting.Results1. Both BRS in response to increases and decreases in blood pressure were significantly reduced in the SHR+Sed group compared to Wistar+Sed group (PE: 0.99±0.15 bpm/mmHg vs. 2.37±0.47 bpm/mmHg, NP: 0.77±0.14 bpm/mmHg vs. 1.60±0.26 bpm/mmHg, P < 0.01). ExT partially normalized the attenuated BRS in SHR(PE: 1.31±0.14 bpm/mmHg;NP: 1.23±0.42 bpm/mmHg,P < 0.05), but had no significant effect on both BRS in Wistar rats.2.Tempol increased BRS induced by PE in the SHR+Sed group, but did not change BRS in other 3 groups. On contrast, DETC reduced BRS in the SHR+ExT group,abolished the benefical effect of ExT on the BRS. DETC also inhibited BRS in both Wistar+Sed and Wistar+ExT groups.3. Compared to Wistar+Sed rats, total antioxidant capacity in the hypothalamus was lower in the SHR+Sed group, whereas MDA content was higher in the SHR+Sed group. ExT not only increased total antioxidant capacity and decreased MDA content in the hypothalamus of SHR but also improved total antioxidant capacity in Wistar rats.4. Enzyme activities of total SOD and CuZn-SOD were reduced in the hypothalamus of SHR compared to Wistar rats (P < 0.01). Enzyme activity of CAT was also reduced in SHR(P < 0.05). ExT significantly enhanced those antioxidant enzyme activities in SHR.5. The protein expression of CuZn-SOD in the PVN was lower in the SHR+Sed group than in the Wistar+Sed group (0.57±0.09 vs. 0.98±0.20, P < 0.01),ExT significantly upregulated CuZn-SOD protein expression in the PVN of SHR (0.85±0.16, P < 0.05), but did not significantly increase CuZn-SOD protein in the Wistar+ExT group. There were no significant differences in Mn-SOD protein expression within the PVN among the 4 groups.Conclusion1. The improvement of baroreflex sensitivity evoked by exercise training in SHR is associated with increases in the activity of major antioxidatant enzymes and antioxidant capacity as well as reduced central oxidative stress.2. Exerciser training-induced upregulation of CuZn-SOD protein expression in the PVN of SHR is related to an increase in SOD enzyme activity, which may contribute to the enhancement of central antioxidant capacity. |
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