The long-term objective of our group is to characterize an interactive role of vasoactive substances in sepsis-induced myocardial dysfunction and related cardiovascular pathologies. Chronic peritoneal sepsis in our rat model produces myocardial dysfunction in an isolated heart preparation and cardiomyocytes. Induction of sepsis also increases susceptibility of the isolated hearts to a calcium paradox-mediated myocardial injury. In vivo, we have demonstrated that induction of sepsis results in disproportionate alterations in the circulating levels of Endothelin-1 (ET-1) and nitric oxide byproducts (nitrite and nitrate, NOx). Recently we observed that inhibition of metalloprotease (endothelin-converting enzyme [ECE], which converts proET-1 to ET-1) at the time of induction of endotoxemia decreased the expression of myocardial inducible nitric oxide synthase (iNOS) and downregulated the expression of p38 mitogen-activated protein kinase (MAPK) twenty-four hours later. Therefore, our immediate objective in the present proposal is to test the hypothesis that sepsis-induced alteration in the biosynthesis of myocardial ET-1 (regulated by ECE-1) via MAPK-dependent or -independent mechanism(s) would affect NOS proteins and cardiac function. The following two specific aims are designed to address this hypothesis.
Specific Aim 1 : To determine if ECE-1 inhibition at the time of induction of sepsis would affect sepsis-induced myocardial dysfunction (decrease in the rates of left ventricular contraction and relaxation, i.e., + dP/dt and -dP/ dt respectively) and the expression of p38MAPK and iNOS proteins at 12 and 24 h post sepsis (Year 1-2).
Specific Aim 2 : To determine if ECE-1 inhibition at the time of induction of sepsis via p38MAPK-dependent or -independent mechanism would affect myocardial function in an isolated heart preparation at 24 h post sepsis (Year 2-3).
The specific aims were designed to assess if ECE-1 inhibition during sepsis would suppress sepsis-induced myocardial dysfunction characterized by downregulation of p38 MAPK and depressed expression of iNOS proteins. The novel aspect of the specific aims is that the results will provide evidence for a causal relationship between ET-1 biosynthesis and the expression of p38MAPK and iNOS proteins in the myocardium. An increased understanding of the underlying mechanisms during these two stages (12 and 24 h post sepsis) of sepsis will help design therapeutic interventions for early and late stages of sepsis.
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