ABNORMAL MYOCARDIAL KINETICS OF I-123 HEPTADECANOIC ACID IN SUBJECTS WITH IMPAIRED GLUCOSE-TOLERANCE

Increased triglyceride accumulation has been observed in the diabetic heart, but it is not known whether the abnormalities in myocardial fat ty acid metabolism differ between insulin-dependent (IDDM) and non-ins ulin-dependent (NIDDM) diabetic patients or whether they are present e ven prior to overt diabetes. Therefore, we studied myocardial fatty ac id kinetics with single-photon emission tomography using I-123-heptade canoic acid (HDA) in four groups of men: impaired glucose tolerance (I GT) (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 s cintigraphy (IGT and NIDDM groups) were performed to study cardiac fun ction and flow. In the IGT subjects, myocardial HDA beta-oxidation ind ex was reduced by 53% (4.6 +/- 0.4 vs 9.7 +/- 1.0 mu mol.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 co mpared with the control subjects (43 +/- 4 vs 61 +/- 4%, p < 0.05). NI DDM patients also tended to have a lowered HDA beta-oxidation index, w hereas IDDM patients had similar myocardial HDA kinetics compared to t he control subjects. Myocardial perfusion imaging during the dipyridam ole-handgrip stress was normal both in the IGT and NIDDM groups, indic ating that abnormal myocardial perfusion could not explain abnormal fa tty acid kinetics. In conclusion, even before clinical diabetes, IGT s ubjects show abnormalities in myocardial fatty acid uptake and kinetic s, These abnormalities may be related to disturbed plasma and cellular lipid metabolism.