A major goal of this continuation proposal is to answer the question: """"""""What would happen if we removed the beta-hydroxy group of norepinephrine and epinephrine and replaced it with fluorine, stereospecifically? We have recently developed the synthetic methods to perform this transformation. These novel beta-fluoro cogeners will be evaluated for their ability to masquerade as the native catecholamines at the numerous adrenergic recognitions sites in the heart. The biomimetic potency of these [19F]fluoro analogs will be compared by measuring the in vitro binding affinities for eight adrenergic receptor types, the norepinephrine transporter (NET), and the vesicular monoamine transporter. The tracer kinetics of the [18F]-labeled analogs will be compared ex vivo in the perfused rat heart and in vivo in PET imaging studies with dogs to determine their neuronal and vesicular selectivities. The applicants hypothesize that the respective 1S-beta-fluoro derivatives of DA and N-methyl-DA may act as dopamine-beta-hydroxylase (DBH) substrates. Thus, DBH hydroxylation of these tracers could provide a direct measure of heart DBH activity by determining the efflux rate of [18F]fluoride ion derived from breakdown of the highly unstable fluorohydrin intermediate. This laboratory has developed the false neurotransmitter [11C]meta-hydroxyephedrine (HED) and the endogenous neurohorome [11C]epinephrine (EPI) to study different aspects of sympathetic nerve function by PET. Retention of HED in heart is predominantly uptake-1 dependent whereas the retention of EPI, like norepinephrine itself, is dependent on vesicular storage. A second goal of this proposal is to investigate the effects of known and putative cardioactive agents on the kinetics of HED and EPI. The isolated perfused working rat heart will be used to screen drugs for robust effects. These drugs will then be tested further in dog heart using in vivo PET imaging. Drugs that will be initially evaluated include: 1) the neurotoxins MPTP and MPP+; 2) over-the-counter medications containing sympathomimetics, such as Sudafed; 3) the """"""""street drugs"""""""" cocaine and MDMA.
The third aim of this proposal is to synthesize highly polar derivatives of desipramine to map neuronal NET density in the heart. Lowering the log P of DMI substantially by incorporating highly polar groups in the 2-position should diminish non-neuronal binding and enhance prospects for deriving NET density data from tracer kinetic modeling.
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