Hypertensive patients have a limited tolerance to exercise, but the mechanisms for this limitation are not known. Studies in chronically instrumented dogs indicate that an alpha1-adrenergic constrictor tone competes with coexisting metabolic and endothelial mediated vasodilation in the coronary vasculature during exercise. Data also indicate that a coronary constrictor tone is exaggerated in dogs with renovascular hypertension. The goal is to determine the adrenergic and neurohumoral mechanisms responsible for the greater coronary vascular resistance after renovascular hypertension. The overall hypothesis to be tested is that renovascular hypertension alters the neural, paracrine and autocrine control systems of the coronary circulation through exacerbation of vasoconstrictor inputs and attenuation of vasodilator influences. These alterations would cause exaggerated vasoconstrictor reflex influences on the coronary vessels and a reduced ability to increase coronary blood flow. We propose that renovascular hypertension causes an imbalance between vasoconstrictor and dilator mechanisms and results in a reduction in myocardial work efficiency and increased susceptibility to myocardial hypoperfusion and ischemia, especially during exercise. The long-range goal is to demonstrate that coronary blood flow regulation is the result of interactions between neurohormonal and endothelial control mechanisms, but under pathophysiological conditions, the balance between these control mechanisms is altered such that vasoconstriction dominates. The results of these experiments should address fundamental questions regarding alterations in sympathetic nervous system and endothelial function and the mechanisms by which these systems are altered by renovascular hypertension. These studies should clarify the mechanistic rationale for different medical therapies to treat patients with hypertension. The following hypotheses using both in vivo conscious instrumented dog and in vitro isolated coronary vessel models will be addressed. 1) Renovascular hypertension increases coronary vasoconstriction at rest and during exercise such that the myocardium, specifically the endocardium, becomes hypoperfused relative to oxygen demand. 2) Renovascular hypertension induced changes in coronary vascular function are due to adaptations in the vascular neural-humoral control mechanisms.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
3R01HL059405-02S2
Application #
6078844
Study Section
Respiratory and Applied Physiology Study Section (RAP)
Project Start
1998-01-15
Project End
2001-12-31
Budget Start
1999-06-01
Budget End
1999-12-31
Support Year
2
Fiscal Year
1999
Total Cost
Indirect Cost
Name
University of North Texas
Department
Physiology
Type
Schools of Osteopathy
DUNS #
110091808
City
Fort Worth
State
TX
Country
United States
Zip Code
76107
Carroll, Joan F (2003) Isolated heart responsiveness to beta-simulation after exercise training in obesity. Med Sci Sports Exerc 35:548-54
Carroll, Joan F; Kyser, Cheryl K (2002) Exercise training in obesity lowers blood pressure independent of weight change. Med Sci Sports Exerc 34:596-601
Brandt, M A; Gwirtz, P A (2001) Exercise training reduces ischemic myocardial dysfunction. Med Sci Sports Exerc 33:556-63