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

Objective To investigate whether training changes skeletal muscle venular p rofile and hemodynamic responses to exercise we studied spontaneously hyper tensive rats (SHR) and Wistar-Kyoto (WKY) rats submitted to training progra mme (T = 50-60% of VO(2)max). Design 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 chro nically instrumented for hindlimb flow (HLF) and arterial pressure (AP) mea surements at rest, during dynamic exercise and recovery in two different si tuations: control and after extensive intravenous blockade (hexamethonium losartan + N-omega-nitro-L-arginine methyl ester + hydralazine), For morph ometric analysis, skeletal muscle samples (gracilis) were obtained after tr anscardiac perfusion with fixative. Results T caused a significant reduction of resting mean arterial pressure (MAP) (-11%) only in the SHR group without changing basal HLF. In the seden tary SHR (SHRS), basal relative hindlimb resistance was increased by 45%, b ut was significantly reduced after T (P < 0.05), During dynamic exercise, M AP increased similarly (10-20 mm Hg) in all groups. HLF increases were simi lar 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 incr ease 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 redu ction (-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. Conclusions The results suggest that increased venule density is a specific adaptation of SHR skeletal muscle to training. Venular growth may contribu te to both the pressure-lowering effect and the large HLF at high exercise intensities observed in the trained SHR. J Hypertens 19:931-940 (C) 2001 Li ppincott Williams & Wilkins.