The characteristics of I-125 4-IQNB and H-3 QNB in vivo and in vitro.

The accumulation of (R)-(H-3)-3-quinuclidinyl benzilate (H-3 QNB) and (R,S)-1-azabicyclo(2.2.2)oct-3-yl (R,S)-alpha-hydroxy-(4-[I-125]iodophenyl) benzeneacetate (I-125 4- IQNB ) in heart, caudate/putamen, and cerebellum of rats was determined at intervals from 15 min to 4 hr after injection. The behavior of the two radiotracers in the heart is consistent with in vitro results with respect to affinities and specificities. In the brain, however, the compounds differ in tissue selectivity. At high specific activity, neither compound provides localization that is consistent with the concentration of receptor in the tissues. The results of this study do not indicate quantification of receptor concentration by means of single external images.