Abnormal myocardial kinetics of 123I-heptadecanoic acid in subjects with impaired glucose tolerance

Abstract

Increased triglyceride accumulation has been observed in the diabetic heart, but it is not known whether the abnormalities in myocardial fatty acid metabolism differ between insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) diabetic patients or whether they are present even prior to overt diabetes. Therefore, we studied myocardial fatty acid kinetics with single-photon emission tomography using 123I-heptadecanoic acid (HDA) in four groups of men: impaired glucose tolerance (IGT) (n = 13, age 53 ± 2 years, mean ± SEM), IDDM (n = 8, age 43 ± 3 years), NIDDM (n = 10, age 51 ± 2 years) and control subjects (n = 8, age 45 ± 4 years). Echocardiography and myocardial perfusion scintigraphy (IGT and NIDDM groups) were performed to study cardiac function and flow. In the IGT subjects, myocardial HDA beta-oxidation index was reduced by 53% (4.6 ± 0.4 vs 9.7 ± 1.0 μmol · min-1 · 100 g-1, p < 0.01) and HDA uptake by 34% (3.7 ± 0.2 vs 5.6 ± 0.3% of injected dose 100 g, p < 0.01) compared with the control subjects. The fractional HDA amount used for beta-oxidation was lower in the IGT compared with the control subjects (43 ± 4 vs 61 ± 4%, p < 0.05). NIDDM patients also tended to have a lowered HDA beta-oxidation index, whereas IDDM patients had similar myocardial HDA kinetics compared to the control subjects. Myocardial perfusion imaging during the dipyridamole-handgrip stress was normal both in the IGT and NIDDM groups, indicating that abnormal myocardial perfusion could not explain abnormal fatty acid kinetics. In conclusion, even before clinical diabetes, IGT subjects show abnormalities in myocardial fatty acid uptake and kinetics. These abnormalities may be related to disturbed plasma and cellular lipid metabolism.