Exercise training causes skeletal muscle venular growth and alters hemodynamic responses in spontaneously hypertensive rats

Author(s)

Amaral, Sandra L. ^[1] ; Silveira, Neide P. ; Zorn, Telma M. T. ; MIchelini, Lisete C.

Affiliation

^[1] Universidade de São Paulo (USP). Instituto de Ciências Biomédicas. Departamento de Biologia Celular e do Desenvolvimento - Brasil

• Document type: Journal article
• Source: Journal of Hypertension; v. 19, n. 5, p. 931-940, May 2001.
• Field of knowledge: Biological Sciences - Physiology

Abstract

o investigate whether training changes skeletal muscle venular profile and hemodynamic responses to exercise we studied spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats submitted to training programme (T = 50-60% of VO(2)max). Training (T) was performed on a treadmill over a period of 13 weeks. Age-matched control groups were kept sedentary (S), T and S rats were chronically instrumented for hindlimb flow (HLF) and arterial pressure (AP) measurements at rest, during dynamic exercise and recovery in two different situations: control and after extensive intravenous blockade (hexamethonium + losartan + N-omega-nitro-L-arginine methyl ester + hydralazine), For morphometric analysis, skeletal muscle samples (gracilis) were obtained after transcardiac perfusion with fixative. T caused a significant reduction of resting mean arterial pressure (MAP) (-11%) only in the SHR group without changing basal HLF. In the sedentary SHR (SHRS), basal relative hindlimb resistance was increased by 45%, but was significantly reduced after T (P < 0.05), During dynamic exercise, MAP increased similarly (10-20 mm Hg) in all groups. HLF increases were similar for the four groups up to 0.8 km/h; at higher workloads, HLF was higher in trained SHR (SHRT) versus trained WKY (WKYT) (3.9- versus 2.9-fold increase over basal HLF, respectively). After blockade (and pressure correction with IV phenylephrine infusion), steady-state exercise was performed with similar hindlimb vasodilation in all groups and was accompanied by MAP reduction (-17 <plus/minus> 8 mmHg) only in SHRT group. Skeletal muscle venular profile (density, diameter and lumen cross-sectional area) was similar in WKYT, WKYS and SHRS, but significantly increased in SHRT. In this group the two-fold increase in venule density was correlated with both the reduction in baseline MAP and the increase in HLF during dynamic exercise. The results suggest that increased venule density is a specific adaptation of SHR skeletal muscle to training. Venular growth may contribute to both the pressure-lowering effect and the large HLF at high exercise intensities observed in the trained SHR. (AU)