The long-term objective of the studies outlined in this proposal is to determine how chronic arterial hypertension and hypercholesterolemia, two major risk factors for ischemic diseases of the heart, brain, gut and other tissues, enhance the microvascular dysfunction and inflammatory responses normally elicited by ischemia/reperfusion (I/R). Normotensive (WKY) and genetically-hypertensive (SHR) rats with normal or elevated serum cholesterol levels, as well as cholesterol ester transfer protein (CETP) transgenic and LDL receptor knockout mice will be studied. Leukocyte-endothelial cell adhesion, platelet-leukocyte aggregation, mast cell degranulation, albumin leakage, and oxidant production will be monitored in the mesenteric microvasculature of these animal models after I/R.
One specific aim will focus on the microvascular responses to varying durations of ischemia followed by reperfusion. These experiments will determine whether arterial hypertension, hypercholesterolemia, or a combination of the two risk factors renders the microvasculature more vulnerable to I/R-induced inflammation and tissue injury. The second specific aim is to assess the contributions of enhanced oxidant production and/or decreased nitric oxide (NO) generation to the exaggerated inflammatory responses elicited by I/R in animals with hypertension, hypercholesterolemia or both. The oxidation of dihydrorhodamine 123 will be used to monitor oxidant production by different cellular elements within and surrounding postcapillary venules. Blood nitrate/nitrite levels and nitric oxide synthase activity will be used to monitor NO generation in postischemic tissues. L-arginine and certain analogues of this amino acid, as well as NO donors, will be used to manipulate NO levels in the various models. Studies are also proposed to assess potential modulatory influences of superoxide, hydrogen peroxide, and xanthine oxidase. The third specific aim is to define the contributions of leukocytes, platelets, and mast cells to the exaggerated inflammatory responses and microvascular dysfunction elicited by I/R in animals with hypertension, hypercholesterolemia or both. Monoclonal antibodies or antagonists directed against different adhesion glycoproteins expressed on leukocytes, platelets, and/or endothelial cells will be used to interfere with leukocyte-endothelial cell adhesion and platelet-leukocyte aggregation. Mast cell stabilizing agents will also be employed to assess the role of mast cell degranulation in the different responses. The results obtained from studies outlined in this proposal should significantly extend our understanding of the mechanisms by which hypertension and hypercholesterolemia contribute to the initiation of vascular injury. Preliminary evidence suggests that hypertension and hypercholesterolemia may be risk factors by virtue of their abilities to affect the responsiveness of microvascular endothelium and circulating cells (leukocytes and platelets) to endogenous inflammatory stimuli.
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