Date of Graduation

2017

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Physiology, Pharmacology & Neuroscience

Committee Chair

Paul D Chantler

Committee Co-Chair

Randall Bryner

Committee Member

Jefferson Frisbee

Committee Member

Mark Olfert

Committee Member

James Simpkins

Abstract

The present study examined the effect of unpredictable chronic mild stress (UCMS) on peripheral microvessel function in healthy and metabolic syndrome (MetS) rodents, and whether exercise training could prevent the vascular dysfunction associated with UCMS. Our initial hypothesis was that: 1) LZRs exposed to UCMS would have peripheral microvascular dysfunction similar to that evident in the OZRs controls due to a reduction in NO bioavailability and an increase in ROS production; 2) the comorbidity between MetS exposed to UCMS will exacerbate the already existing peripheral microvascular dysfunction; 3) exercise could limit the peripheral microvascular dysfunction by decreasing oxidative stress and improving vasodilation associated with MetS exposed to chronic stress; 4) MVD will be reduced in rats exposed to UCMS but loss of MVD will be mitigated by exercise; and 5) the increase in MVD will be reflected by a change in angiogenesis and oxidative markers.;Lean and obese (model of MetS) Zucker rats (LZR; OZR) were exposed to 8 weeks of UCMS, exercise (Ex), UCMS+Ex, or control conditions. At the end of the intervention, gracilis arterioles (GAs) were isolated and hung in a pressurized myobath to assess endothelium-dependent (EDD) and -independent (EID) dilation. Levels of nitric oxide (NO) and reactive oxygen species (ROS) were measured through DAF-FM and DHE staining, respectively. Immunohistochemistry was used to determine the number of pericytes within the cortex and striatum of the brain.;The comorbidity between UCMS and MetS does not exacerbate the effects of one another on GA EDD responses, but does lead to the development of other vasculopathy adaptations, which can be partially explained by alterations in NO and ROS production. Importantly, exercise training alleviates most of the negative effects of UCMS on GA function. Compared to LZR controls, EDD and EID was lower in LZR-UCMS. The OZR-Ex group had a higher EDD and EID, compared to OZR-Controls; whereas only a difference in EDD was noted between LZR-Control and LZR-Ex groups. Importantly, EDD and EID were higher in the LZR and OZR UCMS+Ex groups compared to UCMS alone. Lower NO bioavailability and higher ROS were noted in the LZR-UCMS group, but not OZR-UCMS, compared to controls. Ex and UCMS-Ex groups had higher NO bioavailability compared to control and UCMS groups, but ROS levels remained high. UCMS significantly decreased MVD in LZR-UCMS but was not changed in OZR-UCMS. In LZR- and OZR-Ex, MVD was increased and when coupled with UCMS, Ex improved MVD in both LZR- and OZR-UCMS+Ex. RT-PCR showed no differences in mRNA expression between groups in any of the angiogenic and oxidative stress markers examined.;Corticosterone levels were elevated in the Ex and UCMS+Ex groups vs. the controls which may, in part, reflect the slight stress induced by use of the forced treadmill Ex protocol. It has been shown that glucocorticoids can increase ROS directly, including superoxide, hydrogen peroxide, and peroxynitrite (1). Given that DHE can interact with these oxidants, it could be speculated the higher ROS levels seen in LZR-Ex and UCMS+Ex are a byproduct of increased corticosterone. The fact that in Ex and UCMS+Ex EDD was improved despite elevated corticosterone levels, suggests EDD augmentation was likely mediated from non-corticosterone pathways. Previous studies have also shown glucocorticoids can attenuate angiogenesis by inhibiting proliferation of cerebrovascular endothelial cells. In addition, pericyte apoptosis occurs with increased cortisol levels, where the glucocorticoid binds to receptors expressed on the pericytes to initiate cell death. L-NAME blunted maximum dilation back down to LZR- and OZR-Control+LNAME values, suggesting the Ex augmentation of EDD may be through a NO-dependent pathway. The expression and function of eNOS is upregulated after Ex training due to increased shear stress, thus could explain why EDD in LZR- and OZR-Ex was improved in the skeletal muscle arterioles. One possible factor that could have contributed to the increase in cerebral MVD could be the increase in NO production following Ex. Muscle contraction increases VEGF in the muscle interstitium, where VEGF acts on its receptors within the capillary endothelium to stimulate angiogenic processes, thus providing further support for exercise-induced angiogenesis.

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