AGE-RELATED RESPONSE TO EPINEPHRINE-INDUCED MYOCARDIAL STRESS - A FUNCTIONAL AND ULTRASTRUCTURAL-STUDY

Left ventricular systolic and diastolic function before, during, and after a 2-hour intravenous infusion of epinephrine at either 0.5-mu-g/kg/min or 2-mu-g/kg/min were assessed by pressure-volume data obtained by conductance catheter micromanometer technique and correlated with cardiac ultrastructure and plasma levels of epinephrine in neonatal (3-5 days old, n = 12) versus adult (3-4 months old, n = 11) pigs. Administration of epinephrine at 0.5-mu-g/kg/min resulted in an increase in end-systolic elastance (Ees) only in adults, whereas at 2.0-mu-g/kg/min Ees increased in both groups. After 2-hour administration of epinephrine at 2.0-mu-g/kg/min, Ees decreased significantly (p < 0.05) from the preinfusion baseline value of 8.9 +/- 2 (mean +/- SD) to 5 +/- 1.7 mm Hg/ml, and a significant (p < 0.05) increase in left ventricular volume elasticity (VdP/dV) from 0.4 +/- 0.02 to 1.4 +/- 0.2 mm Hg occurred in neonates versus no change from baseline in either Ees or VdP/dV in the adults. These changes in the neonates were associated with sarcolemmal rupture and mitochondrial Ca2+ granule deposition versus normal cardiac ultrastructure in the adults. We conclude that the neonatal myocardium is more susceptible to cardiotoxicity from circulating epinephrine.