Myocardial extraction of teboroxime: effects of teboroxime interaction with blood.

The isolated perfused rat heart preparation was used to determine whether the interaction of blood with either 99mTc-teboroxime, 99mTc-sestamibi or 201TI affects the extraction of these myocardial perfusion agents. Hearts were retrogradely perfused at 72 cm H2O with Krebs-Henseleit buffer equilibrated with O2:CO2 (95:5). The hearts were paced at 5 Hz. Single-pass extraction of 99mTc-teboroxime (96% +/- 1%) was greater than that of 99mTc-sestamibi (15% +/- 1%) or 201TI (30% +/- 5%). Extraction of the hydroxide form of 99mTc-teboroxime was only 43% +/- 4%. When arterial blood obtained from rats administered 99mTc-teboroxime was injected into the perfused heart, extraction of 99mTc-teboroxime decreased progressively as its time in circulation was lengthened. Similar experiments using either 99mTc-sestamibi or 201TI showed that extraction of these agents was neither affected by the presence of blood nor residence in circulation. For 99mTc-teboroxime, extraction was 99.5% +/- 0.5%, 57% +/- 13%, 20% +/- 2% at 1, 5, and 60 min postinjection, respectively. In separate experiments, HPLC analysis of blood at 5, 15 and 60 min postinjection indicated that only 34% +/- 4%, 13% +/- 2%, and 2% +/- 1%, respectively, of the total 99mTc-teboroxime was free and was associated with extraction values of 44% +/- 7%, 28% +/- 5%, and 19% +/- 3%, respectively. The percentage of this free radioactivity that converted from the chloro to the hydroxide form was 9% +/- 2%, 6% +/- 2%, and 2% +/- 1%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)