Exercise training blunts microvascular rarefaction in the metabolic syndrome

Abstract

son, and Randall Bryner. Exercise training blunts microvascular rarefaction in the metabolic syndrome. Am J Physiol Heart Circ Physiol 291: H2483-H2492, 2006. First published June 23, 2006 doi:10.1152/ajpheart.00566.2006.-Reduced skeletal muscle microvessel density (MVD) in the obese Zucker rat (OZR) model of the metabolic syndrome is a function of a chronic reduction in vascular nitric oxide (NO) bioavailability. Previous studies suggest that exercise can improve NO bioavailability and reduce chronic inflammation and that low vascular NO bioavailability may be associated with impaired angiogenic responses via increased matrix metalloproteinase (MMP)-2 and MMP-9 activity. As such, we hypothesized that chronic exercise (EX) would increase NO bioavailability in OZR and blunt microvascular rarefaction through reduced MMP activity, and potentially via altered plasma cytokine levels. Ten weeks of treadmill exercise (1 h/day, 5 days/wk, 22 m/min) reduced body mass and fasting insulin and triglyceride levels in EX-OZR vs. sedentary (SED) OZR. In EX-OZR, gastrocnemius muscle MVD was improved by 19 Ϯ 4%, whereas skeletal muscle arteriolar dilation and conduit arterial methacholine-induced NO release were increased. In EX-OZR, functional hyperemia was improved vs. SED-OZR, and minimum vascular resistance within perfused gastrocnemius muscle was reduced, although no change in arteriolar stiffness was identified. Western blotting and gelatin zymography demonstrated that neither expression nor activity of MMP-2 or MMP-9 was altered in skeletal muscle of EX vs. SED animals. Plasma markers of inflammation associated with angiogenesis, monocyte chemoattractant protein-1 and IL-1␤, were increased in SED-OZR and were reduced with training, whereas IL-13 was reduced in SED-OZR and increased with exercise. These data suggest that exercise-induced improvements in skeletal muscle MVD in OZR are associated with increased NO bioavailability and may stem from altered inflammatory profiles rather than MMP function. skeletal muscle microcirculation; regulation of skeletal muscle perfusion; microvessel density; vascular remodeling; vascular resistance THE OBESE ZUCKER RAT (OZR) is a model of the metabolic syndrome based on chronic hyperphagia (5, 21). As such, this animal model rapidly becomes obese and develops profound insulin resistance and hypertriglyceridemia, with a clinically relevant hypertension and the genesis of a prothrombotic and proinflammatory state (2,17,24,51). We have previously demonstrated that, with evolution of the metabolic syndrome in the OZR, a progressive reduction in skeletal muscle microvessel density develops that can result in 25% reduction in the total number of microvessels within this tissue compared with levels determined in control animals (14). This rarefaction of the vascular network contributes to an elevation in peripheral vascular resistance in OZR (12, 14, 15) and appears to be largely independent of any developing increase in mean arterial pressure (13). In contrast, ongoing studies in our laborat...

Exercise reduces oxidative stress but does not alleviate hyperinsulinemia or renal dopamine D1receptor dysfunction in obese rats

“…Boor et al do not mention if the rats were fasted overnight, and the triglyceride levels in their study might reflect postprandial/random levels. In addition, our results are similar to those of Frisbee et al (24) who, using 10 wk of exercise and an overnight fasting period, observed a similar decrease in triglyceride levels.…”

Satellite cell proliferation is reduced in muscles of obese Zucker rats but restored with loading

“…Although the OZR is significantly less active than the LZR (9), OZRs have much greater body mass, and this should provide a greater stimulus for muscle growth on the weight-bearing muscles. Nevertheless, a previous study from our laboratory in which the daily activity of the OZR was increased through daily treadmill running demonstrated no increase in the size of their skeletal muscles (18). These findings suggest that there may be an underlying deficit in the ability of skeletal muscle to respond to increased loading in the OZR model of metabolic syndrome.…”

Distinct temporal phases of microvascular rarefaction in skeletal muscle of obese Zucker rats

“…There is an additional lower rate of microvessel loss after 17 wk of age, but our unpublished work suggests that net microvessel loss develops asymptotic behavior after 17 wk of age. What was most interesting about this observation is that our previous results suggested that the change in skeletal muscle microvessel density would parallel the changes to vascular NO bioavailability (21,23). However, as demonstrated in Figs.…”

“…As defined by Goligorsky (26), microvascular rarefaction is a form of microvascular adaptation in response to a challenged or disease state that results in a reduction in arteriolar or capillary density within an affected tissue. In OZR, this process plateaus at an ϳ25% reduction in microvessel density compared with control levels in LZR (21,42,48), with clear implications for mass transport/ exchange and muscle fatigue resistance (46). Furthermore, previous results have demonstrated that this response is not dependent on the development of hypertension in OZR (22) and that it is associated with the development of insulin resistance and low bioavailability of nitric oxide (NO) within the microvasculature (23).…”