Journal of Neuroscience, Vol 9, 2344-2352, Copyright © 1989 by Society for Neuroscience
Non-steady-state measurement of in vivo receptor binding with positron emission tomography: "dose-response" analysis
JS Perlmutter, MR Kilbourn, MJ Welch and ME Raichle
Department of Neurology and Neurological Surgery, Washington University School of Medicine, St. Louis, Missouri 63110.
We previously developed a non-steady-state technique using positron
emission tomography (PET) and the radioligand 18F-spiperone (18F-SP) for
the measurement of in vivo radioligand-receptor binding in brain. The
purpose of this investigation is to determine the sensitivity of this
method to alterations in the apparent number of available specific binding
sites. Nine studies were performed on the same baboon. The animal was
pretreated with varying doses of unlabeled SP (15-600 micrograms) to
compete for specific binding sites. The experimental procedure included
measurement of regional cerebral blood flow, cerebral blood volume, and the
protein binding of 18F-SP in arterial blood. At least 3.5 hr after
pretreatment, no-carrier-added 18F-SP (containing less than 3 micrograms
SP) was administered intravenously. Sequential PET scans and measurements
of arterial-blood radioactivity due to radioligand and its labeled
metabolites continued for 3 hr. A 3- compartment model representing the in
vivo behavior of radioligand was used to analyze the data. As expected, we
found that an index of binding called the combined forward rate constant
(which equals the product of the apparent maximum number of available
specific binding sites and the association rate constant of radioligand for
receptor) declined with increasing dose of unlabeled SP. Other estimated
variables including the dissociation rate constant did not change. This
demonstrates that our non-steady-state method for estimating
radioligand-receptor binding kinetics can detect a decrease in the apparent
number of available specific binding sites. This is an important step in
the validation of this in vivo receptor binding assay and its subsequent
application.