Sympathetic Mechanisms in the Cardiovascular and Metabolic Alterations of Obesity

Continuing Review (CR, 2021/08/04) Update: Removal of the angiotensin receptor blockade arm of the study

The presence of obesity increases the risk for hypertension and diabetes, in part due to the development of insulin resistance. Obesity is also associated with sympathetic activation and the overarching hypothesis is that sympathetic activation contributes to insulin resistance with impairment of its vascular and metabolic actions. Preliminary studies suggest that 1) Blood pressure can be normalized by autonomic blockade in obese hypertensives, 2) Sympathetic activation provides no metabolic benefit because the increase in resting energy expenditure associated with obesity is due to an increase in fat free mass rather than sympathetic activation. On the contrary, autonomic blockade: 3) Improves insulin sensitivity in obese hypertensives, 4) Reverses their impaired NO-mediated dilation, and 5) Reduces plasma isoprostanes, a measure of oxidative stress. Furthermore, these abnormalities are interrelated in negative feedback loops, whereby inflammation/oxidative stress impairs nitric oxide mechanisms, which in turn reduces insulin-mediated vasodilation important for substrate delivery, thus contributing to insulin resistance; insulin resistance leads to compensatory increases in insulin levels, which contributes to further sympathetic activation. Current treatment guidelines do not specifically address the treatment of obesity hypertension, and do not target sympathetic activation as a first line approach. It is important, therefore, to determine whether or not targeting sympathetic activation offers unique advantages in the treatment of obesity hypertension over current approaches. The investigators propose a proof-of-concept mechanistic study comparing the metabolic, vascular, and anti-inflammatory effects of sympathetic inhibition, calcium channel blockade and angiotensin receptor blockade in obesity hypertension. The investigators will test the hypotheses that sympathetic activation contributes to 1) metabolic insulin resistance, which impairs the suppression of endogenous glucose production and the stimulation of glucose uptake normally provided by insulin, 2) vascular insulin resistance, which impairs insulin-mediated vasodilation and microvascular recruitment that normally promote glucose uptake, and 3) inflammation and oxidative stress, which contribute to insulin resistance and hypertension. The proposed studies will gauge the contribution of sympathetic activation to the cardiovascular and metabolic complications of obesity and provide the mechanistic insight to determine whether or not it should foster the efforts currently under way to develop novel therapies targeting sympathetic activation for hypertension.