Exercise Training Attenuates Sympathetic Activity and Improves Morphometry of Splenic Arterioles in Spontaneously Hipertensive Rats

BACKGROUND: Alterations in the structure of resistance vessels contribute to elevated systemic vascular resistance in hypertension and are linked to sympathetic hyperactivity and related lesions in target organs. OBJECTIVE: To assess the effects of exercise training on hemodynamic and autonomic parameters, as well as splenic arteriolar damages in male Wistar Kyoto (WKY) and Spontaneously Hypertensive Rats (SHR). METHODS: Normotensive sedentary (WKY(S)) and trained (WKY(T)) rats, and hypertensive sedentary (SHR(S)) and trained (SHR(T)) rats were included in this study. After 9 weeks of experimental protocol (swimming training or sedentary control), arterial pressure (AP) and heart rate (HR) were recorded in freely moving rats. We assessed the autonomic control of the heart by sympathetic and vagal autonomic blockade. Morphometric analyses of arterioles were performed in spleen tissues. The statistical significance level was set at p < 0.05. RESULTS: Resting bradycardia was observed in both trained groups (WKY(T): 328.0 ± 7.3 bpm; SHR(T): 337.0 ± 5.2 bpm) compared with their respective sedentary groups (WKY(S): 353.2 ± 8.5 bpm; SHR(S): 412.1 ± 10.4 bpm; p < 0.001). Exercise training attenuated mean AP only in SHR(T) (125.9 ± 6.2 mmHg) vs. SHR(S) (182.5 ± 4.2 mmHg, p < 0.001). The WKY(T) showed a higher vagal effect (∆HR: 79.0 ± 2.3 bpm) compared with WKY(S) (∆HR: 67.4 ± 1.7 bpm; p < 0.05). Chronic exercise decreased sympathetic effects on SHR(T) (∆HR: -62.8 ± 2.8 bpm) in comparison with SHR(S) (∆HR: -99.8 ± 9.2 bpm; p = 0.005). The wall thickness of splenic arterioles in SHR was reduced by training (332.1 ± 16.0 µm(2) in SHR(T) vs. 502.7 ± 36.3 µm(2) in SHR(S); p < 0.05). CONCLUSIONS: Exercise training attenuates sympathetic activity and AP in SHR, which may be contributing to the morphological improvement of the splenic arterioles.