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

Abstract

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 (WKYS) and trained (WKYT) rats, and hypertensive sedentary (SHRS) and trained (SHRT) 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 (WKYT: 328.0 ± 7.3 bpm; SHRT: 337.0 ± 5.2 bpm) compared with their respective sedentary groups (WKYS: 353.2 ± 8.5 bpm; SHRS: 412.1 ± 10.4 bpm; p < 0.001). Exercise training attenuated mean AP only in SHRT (125.9 ± 6.2 mmHg) vs. SHRS (182.5 ± 4.2 mmHg, p < 0.001). The WKYT showed a higher vagal effect (∆HR: 79.0 ± 2.3 bpm) compared with WKYS (∆HR: 67.4 ± 1.7 bpm; p < 0.05). Chronic exercise decreased sympathetic effects on SHRT (∆HR: -62.8 ± 2.8 bpm) in comparison with SHRS (∆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 µm2 in SHRT vs. 502.7 ± 36.3 µm2 in SHRS; 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.

Figure 1

Baseline recording of heart rate (1A), systolic arterial pressure (1B), mean arterial pressure (1C) and diastolic arterial pressure (1D) in freely moving rats. WKY_S (sedentary normotensive rats); WKY_T (trained normotensive rats); SHR_S (sedentary hypertensive rats); SHR_T (trained hypertensive rats). Bars in figures 1A and 1C represent mean ± SD. Results in figures 1B and 1D are expressed as median (interquartile range). ^#p < 0.05 vs. WKY_S; *p < 0.001 vs. WKY_S; ^†p < 0.001 vs. WKY_T and ^‡p < 0.001 vs. SHR_S.

Figure 2

Effects of exercise training on the tonic autonomic control of the heart rate (HR) in non-anesthetized rats. (2A) vagal and (2B) sympathetic effects were obtained, respectively, by the difference between vagal blockade (by atropine) or sympathetic blockade (by propranolol) and resting HR. (2C) Sympathovagal balance was expressed by the tonic sympathovagal index, which is the ratio between resting and intrinsic HR (iHR). (2D) Intrinsic HR (bpm) obtained after autonomic double pharmacological blockade. Bars represent mean ± SD. *p < 0.05 vs. WKY_S; ^†p < 0.05 vs. WKY_T and ^‡p < 0.05 vs. SHR_S.

Figure 3

Correlation coefficient between sympathetic effect and outer wall thickness (A), sympathetic effect and total area thickness (B), sympathovagal index and outer wall thickness (C), sympathovagal index and total area thickness (D).