Preservation of cardiac metabolic capacity after acute catecholamine injury

Abstract

High concentrations of adrenergic agonists are known to cause significant structural damage to the heart, accompanied by depressed cardiac performance. These studies were undertaken to further elucidate mechanisms that contribute to this process. Rabbits were infused with either norepinephrine (NE, 3 micrograms.min-1.kg-1 iv) for 90 min or with an equivalent volume of normal saline (controls). The heart was immediately extracted and studied as an isolated working heart preparation perfused with erythrocyte-enhanced buffer. Stroke work, coronary flow, and O2 metabolism were determined, and substrate oxidation was measured by [14C]glucose or palmitate. Stroke work performed by hearts exposed to NE was only 31% of controls (2.6 +/- 0.4 vs. 8.4 +/- 0.9 g.cm-1.g-1). This was matched by reductions in coronary flow and O2 metabolism. Glucose oxidation was reduced from 54.6 +/- 3.9 to 16.0 +/- 5.3 nmol.min-1.g-1, and palmitate oxidation from 49.8 +/- 5.3 to 21.0 +/- 4.1 nmol.min-1.g-1 in the NE group. However, ATP, creatine phosphate, glycogen, and triacylglycerol concentrations were identical with the control group. O2 delivery per unit substrate oxidation was not lower in the NE group, and O2 extraction did not differ significantly. These findings indicate that the markedly lower contractile performance of the hearts exposed to NE cannot be attributed to a deficiency of metabolic capacity or limitation of O2 or substrate availability because of vasospasm. In view of the brief time (90 min), it is unlikely that leukocyte accumulation was a major factor. The observations are consistent with NE-derived oxidant injury, possibly causing disordered excitation-contraction coupling.