ABC | Volume 110, Nº3, March 2018

Original Article Lemos et al Exercise improves splenic arterioles In SHR Arq Bras Cardiol. 2018; 110(3):263-269 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). A C D B 900 900 800 800 700 700 700 700 600 600 600 600 500 500 500 500 400 400 400 400 300 300 300 300 200 200 200 200 100 100 r = 0.67 p < 0.005 r = 0.52 p < 0.05 r = 0.64 p < 0.005 r = 0.72 p < 0.001 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 0.8 0.9 1.0 1.1 1.2 1.3 1.4 0.8 0.9 1.0 1.1 1.2 1.3 1.4 Outer wall thickness (µm 2 ) Outer wall thickness (µm 2 ) Total area thickness (µm 2 ) Total area thickness (µm 2 ) Sympathetic effect Sympathetic effect Sympathovagal index Sympathovagal index WKY S WKY T SHR S SHR T antihypertensive treatment should aim not only to reduce AP but also to correct injuries associated with hypertension, such as the altered vascular structure. A previous study has shown the efficacy of training to normalize arteriole wall/lumen ratio, evidencing that arteriolar response as well as vascular resistance reduction after exercise training were significantly correlated with AP reduction. 21 Experimental study has found that arteriole wall/lumen ratios were reduced by increased internal and/or external diameter, which is a characteristic pattern for vascular remodeling. 21 Of importance is the demonstration that exercise training, by reversing lumen encroachment, normalizes enlarged wall/lumen ratio of small arterioles in hypertensive rats. These data are in accordance with the results found in our study. Results from studies with animal models indicate that a sustained elevation of sympathetic tonus stimulates smooth muscle cell hypertrophy, suggesting that sympathetic overactivity may contribute to changes in arterial wall thickness. 22 In this way, an interesting finding in our study was a positive and significant correlation between sympathetic hyperactivity and splenic arterioles wall thickness in hypertensive rats, corroborating with results from other investigators who demonstrated that hypertension is associated with sympathetic overactivity that alters vasomotor control resulting in several abnormalities in tissue microcirculation, such as increased arteriolar wall-to-lumen ratio and decreased vessel density, which contribute to maintain an elevated total peripheral resistance. 23-28 Another important finding in our research was that exercise training was able to attenuate sympathetic activity in SHR and that this effect was associated with a reduction in splenic arteriole wall thickness. Exercise training produces beneficial effects on cardiovascular system in normal and sick people via alterations (or modifications) in the neural control of circulation. 29,30 These effects include reductions in AP, sympathetic outflow in humans, 31,32 as well as in animal models, 33,34 and vascular resistance. 35,36 In addition, there is evidence that exercise training improves the conditions of the small vessels in SHR subjected to swimming protocol. 37 Although this study did not address the mechanisms responsible for training-induced effects, one might speculate that arteriole adjustments are group-specific (hypertensive rats) and probably not dependent on paracrine, autocrine, metabolic, and/or myogenic factors, since similar alterations were observed in a previous study. 17 267