A controversy persists as to whether cardiopulmonary bypass (CPB) decreases 
plasma levels of triiodothyronine (T3), thereby justifying peri-operative 
administration of T3 to improve haemodynamic recovery. To examine the effects of 
T3 therapy on post-CPB haemodynamics and to determine whether the potential 
inotropic effects of T3 are mediated by an increase in beta-adrenergic 
responsiveness, a prospective, randomized, double-blind, placebo-controlled 
study was performed in 20 patients undergoing cardiac surgery with CPB. T3 or 
placebo solution (10 patients in each group) was given intravenously at the time 
of aortic unclamping and 4, 8, 12 and 20 h thereafter. End points included (1) 
thyroid hormone levels measured by radioimmunoassay (2) standard haemodynamic 
parameters (3) the density of lymphocyte beta-adrenoceptors measured by a 
radioligand (125I-iodocyanopindolol) binding technique. Post-CPB values (cross 
clamp removal) of T3 (pg.ml-1) were not significantly decreased compared with 
pre-CPB values: 3.3 +/- 0.2 vs 3.1 +/- 0.2 in controls and 3.3 +/- 0.4 vs 3.7 
+/- 0.6 in T3-treated patients, respectively. The haemodynamic parameters were 
no different between the two groups at any postoperative time point. Likewise, 
density and affinity of lymphocyte beta-adrenoceptors were not significantly 
different from pre-operative values in either group. Thus, there seems to be no 
sound justification for a routine use of T3 in patients undergoing open-heart 
procedures.