Positron emission tomography-imaging studies in animal models comparing dopamine agonist and antagonist radiotracers, with respect to their vulnerability to competition by endogenous dopamine, suggest that dopamine agonist radiotracers are more displaceable than antagonist radiotracers following an acute amphetamine challenge. The study by Narendran et al. was the first in healthy human subjects undertaken in response to recent investigations suggesting that the greater vulnerability of agonist radiotracers performed in anesthetized animal models may not be valid in humans. The use of an agonist radiotracer [11C](−)-N-propyl-norapomorphine and the reference antagonist [11C]raclopride in healthy human subjects demonstrated a greater reduction in binding of the agonist relative to the antagonist after amphetamine challenge; however, other binding parameters failed to demonstrate a significant difference. This study does not unequivocally demonstrate the superiority of D2 agonist over D2 antagonist radioligands, but these data add to the growing literature that suggests that D2 agonist radiotracers are more vulnerable to endogenous dopamine competition.
See article at J Pharmacol Exp Ther 2010, 333:533–539. (8915)
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics