Documentation of profound changes in serum
thyroid hormone concentrations associated with
cardiac arrest and
resuscitation, as well as other acute emergencies, have spurred evaluation of possible therapeutic
thyroid hormone administration. Acute and significant, this state, characterized by abnormally low serum
thyroid hormone concentrations, may indicate selective thyroid replacement
therapy. In a previous investigation, post-
resuscitation infusion of
levothyroxine sodium (L-T4) to normalize serum 3,5,3'-triiodothyronine (T3) concentrations was associated with significant reduction of
neurologic deficit caused by severe global
cerebral ischemia. Since L-T4 has been reported to act directly or via one of its metabolites, most likely T3, this most active form of
thyroid hormone was tested. When L-T4 reduced the
neurologic deficit, an increase in
3,3',5'-triiodothyronine (rT3) was also observed. This study therefore determined whether a post-
resuscitation treatment with either T3 (n = 8) or rT3 (n = 8) provided protection against global
cerebral ischemia comparable to that of L-T4. Global
cerebral ischemia was achieved with 9 min of
ventricular fibrillation. Following
resuscitation, one of three solutions (saline group as a control) was infused for 24 h at rates that reproduced the normal serum T3 concentrations or the rT3 concentrations achieved previously during the L-T4
therapy. The successful elevation of T3 and mimicking rT3 concentrations was assessed and confirmed by radioimmunoassay (RIA). In addition, TSH levels were measured by a novel RIA specific for canine
thyroid-stimulating hormone (cTSH).
Neurologic deficit was assessed with a well-standardized
neurologic deficit examination. In contrast to previous studies using L-T4 infusion, no significant reduction of
neurologic deficit was observed. Serum
thyroid hormone changes confirmed previously described decreases and in no case did changes in cTSH appear causal in these changes. Thus, we concluded that L-T4 may offer a therapeutic advantage over T3 or rT3.