This proposal exploits the opportunity for a comprehensive 13C NMR evaluation of fatty acid handling within the intact, functioning heart. The overall goal is to further develop and apply our kinetic 13C NMR methods to study the reciprocal relationship between the activity of the key regulator of fatty acid oxidation, carnitine palmitoyl transferase I (CPTI) and turnover of the myocardial triglyceride pool in normal and diabetic animal models. New and exciting findings from the previously funded period enable 13C NMR to distinguish between oxidative rates in the mitochondria and the rate of long chain fatty acid transport, via CPT1, as well as detect the incorporation rate of 13C-enriched palmitate into the myocardial triglyceride pool, all in the intact, beating heart. Therefore, this study explores the hypotheses that: 1) changes in the regulation of long chain fatty acid oxidation, via CPT1 activity, mediate the turnover rate of myocardial triglycerides and can be evaluated in whole hearts by a comprehensive examination of 13C enrichment kinetics; 2) Alterations in triglyceride content and turnover in the diabetic myocardium occur due to a combination of hyperlipidemia and changes in the expression of genes encoding enzymes for fatty acid uptake and oxidation pathways and that these can be distinguished via 13C NMR as independent mediators in the pathogenesis of diabetic cardiomyopathy. This hypothesis will be tested in both in both rat and mouse models of normal, diabetic, and genetically altered cardiac phenotypes. Specific aims are: 1) Determine reciprocal effects of fatty acid oxidation rates on triglyceride turnover via cardiac 13C NMR during partial inhibition of CPT1; 2) Examine long chain fatty acid oxidation rates, CPT1 activity, and triglyceride pool turnover in the hearts of rats with type-I (insulin deficient) diabetes and test for a potential link between triglyceride accumulation and turnover and the activation of protein kinase C; 3) Investigate effects of triglyceride pool size on the reciprocal nature of CPT1 activity and triglyceride turnover in a transgenic mouse model, overexpressing peroxisome proliferator-activated receptor alpha (PPAR-alpha), that mimics the diabetic phenotype for fatty acid and glucose metabolism and allows for dietary control of myocardial triglyceride pool size; 4) Examine long chain fatty acid oxidation rates, CPT1 activity, and triglyceride turnover in a more clinically relevant animal model of type II (insulin resistant) diabetes, the db/db mouse model, versus non-diabetic, wild-type mice.