Dynamic SPECT imaging of dopamine D2 receptors in human subjects with iodine-123-IBZM

J. P. Seibyl, S. W. Woods, S. S. Zoghbi, R. M. Baldwin, H. M. Dey, A. W. Goddard, Y. Zea- Ponce, G. Zubal, M. Germine, E. O. Smith, G. R. Heninger, D. S. Charney, H. F. Kung, A. Alavi, P. B. Hoffer, R. B. Innis

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We studied the uptake, distribution, metabolism and washout of the dopamine D2 receptor ligand [123I]IBZM in healthy subjects (n = 12) with dynamic brain SPECT. The highest radioactivity level was detected in the striatum. Operationally-defined striatal 'specific' uptake peaked at 69 min postinjection of radioligand and showed a gradual decline of 15% per hour thereafter. 'Specific' uptake at maximal counts represented 53% of the total striatal radioactivity. Two subjects received haloperidol (20 μg/kg i.v.) 80 min postinjection of radioligand. Haloperidol caused a 2.6-fold increase in the rate of washout of specific striatal activity in comparison to that in the 10 control subjects and was consistent with drug-induced displacement of radioligand from the dopamine D2 receptor. Two classes of metabolites were detected in plasma and urine: a polar fraction, not extracted by ethyl acetate, and a nonpolar, extractable fraction consisting of parent compound and two compounds having shorter retention times on reversed-phase HPLC. Greater than half the plasma parent was metabolized within 10-15 min after administration. The volume of distribution, estimated from the peak arterial plasma concentration at 50-75 sec, was 7.7-10.21; the free (nonprotein bound) fraction of [123I]IBZM after in vitro incubation with blood or plasma was 4.4% ± 0.4%. These results suggest that [123I]IBZM exhibits uptake in brain regions with high D2 receptor density and shows a relatively stable washout during which drugs affecting dopaminergic transmission may be administered.

Original languageEnglish (US)
Pages (from-to)1964-1971
Number of pages8
JournalJournal of Nuclear Medicine
Issue number11
StatePublished - Jan 1 1992

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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    Seibyl, J. P., Woods, S. W., Zoghbi, S. S., Baldwin, R. M., Dey, H. M., Goddard, A. W., Zea- Ponce, Y., Zubal, G., Germine, M., Smith, E. O., Heninger, G. R., Charney, D. S., Kung, H. F., Alavi, A., Hoffer, P. B., & Innis, R. B. (1992). Dynamic SPECT imaging of dopamine D2 receptors in human subjects with iodine-123-IBZM. Journal of Nuclear Medicine, 33(11), 1964-1971.