THE EFFECT OF TRIIODOTHYRONINE ON MYOCARDIAL CONTRACTILE PERFORMANCE AFTER EPINEPHRINE EXPOSURE - IMPLICATIONS FOR DONOR HEART MANAGEMENT

Background: This study analyzes in the experimental model of isolated human atrial myocardium whether the myocardial contractile depression occurring after high-dose/long-term catecholamine exposure las typical ly occurring in brain-dead organ donors) can be reversed by thyroid ho rmone administration. Methods: Isolated trabeculae were prepared from atrial myocardium from patients undergoing coronary artery bypass (n = 15). Initial measurements of isometric force were carried out (measur ement conditions of 37 degrees C, Krebs Henseleit solution, supramaxim al electrical stimulation, 1 Hz, at optimal length). Then the trabecul ae were incubated for 6 hours at 26 degrees C in a Krebs Henseleit sol ution containing epinephrine 10(-7) mol/L and the fluorescent dye FURA -2/AM for calcium measurements. At the end of the incubation period, i sometric force, isotonic shortening, and intracellular calcium transie nt (FURA-2 ''ratio method'') were measured. After 30 minutes administr ation of triiodothyronine (5 x 10(-9) mol/L), the measurements were re peated. Control groups included 6 hours incubation in 4 degrees C Kreb s Henseleit solution (n = 5); 6 hours incubation in 26 degrees C FURA- 2/AM (n = 5); and 6 hours incubation in epinephrine 10-7 mol/L (n = 5) . Conclusion: In the model of isolated human myocardium, experimental depression of the contractile performance resulting from long-term cat echolamine exposure could be reversed by a 30-minute triiodothyronine incubation. The experimental data showing increased force amplitudes a t unaltered amplitudes of the intracellular calcium transient and an e ven-reduced calcium time integral provide strong evidence for a sensit ization of the contractile apparatus for calcium by triiodothyronine. The data provide additional knowledge to explain the successful admini stration of triiodothyronine in donor heart management.