Eleven insulin-dependent diabetic patients (IDDM) with angiographically normal coronary arteries and normal echocardiographic dipyridamole test, and 12 normal controls were studied at rest and after atrial pacing. Simultaneous sampling from arterial and coronary sinus blood was performed. In IDDM patients, despite hyperglycemia, myocardial glucose uptake was slightly lower than in controls. This process was significantly activated in both groups by atrial pacing. The isotopically calculated net flux of lactate across myocardium, in agreement with the net balance value based on unlabeled lactate-pyruvate arterio-venous differences, showed a net uptake in controls (3.5 +/- 0.6 mumol/min/1.73 m2) and a net release in IDDM (12.4 +/- 2.6; p less than 0.01). Atrial pacing stimulated lactate uptake in both groups. Myocardial uptake of ketone bodies was significantly higher in IDDM than in controls (37.0 +/- 6.3 mumols/min/1.73 m2 vs 10.1 +/- 3.4; p less than 0.01). Free fatty acid uptake was also significantly greater in IDDM than in controls (44.1 +/- 7.0 mumols/min/1.73 m2 vs 24.1 +/- 5.1; p less than 0.01). Alanine and branched chain amino-acids were released by diabetics but not by control hearts at rest. The normalization of blood glucose concentrations restored normal patterns of lactate and ketone body kinetics across diabetic myocardium.
In conclusion: at rest, myocardial lactate and aminoacids uptake is markedly impaired in IDDM without coronary artery disease; the metabolic abnormalities of the diabetic myocardium is not a primary phenomenon but rather a consequence of hypoinsulinemia and hyperglycemia because insulin administration, resulting in normoglycemia, restored normal patterns of cardiac metabolism.