Dependence of Cardiac Systolic Function on Elevated Fatty Acid Availability in Obese, Insulin-Resistant Rats

• Ex vivo cardiac pump function of obese rats is compromised when glucose is the only substrate.
• Fatty acids normalize cardiac pump function ex vivo in hearts from obese rats.
• Elevated fatty acid levels are important to maintain normal LV systolic function in obesity.

BackgroundClinical data advocating an adverse effect of obesity on left ventricular (LV) systolic function independent of comorbidities is controversial. We hypothesized that in obesity with prediabetic insulin resistance, circulating fatty acids (FAs) become a valuable fuel source in the maintenance of normal systolic function.MethodsMale Wistar rats were fed a high caloric diet for 32 weeks to induce obesity. Myocardial LV systolic function was assessed using echocardiography and isolated heart preparations.ResultsAortic output was reduced in obese rat hearts over a range of filling pressures (for example: 15 cmH2O, obese: 32.6 ± 1.2 ml/min vs control: 46.2 ± 0.9 ml/min, P < .05) when perfused with glucose alone. Similarly, the slope of the LV end-systolic pressure-volume relationship decreased, and there was a right shift in the LV end-systolic stress-strain relationship as determined in Langendorff perfused, isovolumic rat heart preparations in the presence of isoproterenol (10−8M) (LV systolic stress-strain relationship and a reduced load-independent intrinsic systolic myocardial function, obese: 791 ± 62 g/cm2 vs control: 1186 ± 74 g/cm2, P < .01). The addition of insulin to the perfusion buffer improved aortic output, whereas the addition of FAs completely normalized aortic output. LV function was maintained in obese animals in vivo during an inotropic challenge.ConclusionsElevated circulating FA levels may be important to maintain myocardial systolic function in the initial stages of obesity and insulin resistance.