Effects of substrate availability on myocardial C-11 palmitate kinetics by positron emission tomography in normal subjects and patients with ventricular dysfunction
The possibility of demonstrating noninvasively with C-11 palmitate and positron emission tomography (PET) changes in myocardial substrate metabolism in normal and diseased human myocardium in response to altered substrate availability in blood and disease-related abnormalities was examined in five normal volunteers and 16 patients with ventricular dysfunction. C-11 palmitate injection and serial PET imaging were performed after an overnight fast (control period) and again 2 hours later after oral glucose (50 gm). Myocardial C-11 time-activity curves from serial PET images revealed a biexponential clearance pattern. An early rapid phase, defined by relative size and clearance half-time, reflects C-11 palmitate oxidation and the late slow phase tracer deposition in the endogenous lipid pool. During the control period, the tracer fraction entering the early rapid phase averaged 47 +/- 13% (SD) in normal subjects and 45 +/- 12% in patients. Corresponding clearance half-times were 19 +/- 7 and 20 +/- 5 minutes, respectively. Heart rate and blood pressure remained unchanged after glucose, but plasma glucose levels rose by 72.5% in normal subjects and by 98.9% in patients, while free fatty acid levels fell by 72% and 42% respectively. In normal subjects, the tracer fraction in the early rapid phase fell by 43% (p less than 0.005) and the clearance half-time increased by 46%. In patients, the response of C-11 palmitate tissue kinetics to glucose was variable. In nine patients, it was similar to normal subjects while in the other seven patients, the tracer fraction entering the rapid clearance phase increased after glucose by 30% (p less than 0.05) associated with a 36% (p less than 0.05) decline in clearance half-times. This was unrelated to disease etiology or plasma substrate levels but occurred mostly in left ventricles with more severely depressed function.
- Research Organization:
- Univ. of California, Los Angeles
- OSTI ID:
- 5330593
- Journal Information:
- Am. Heart J.; (United States), Vol. 6
- Country of Publication:
- United States
- Language:
- English
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