The effects of carbidopa on the metabolism of 6-( sup 18 F)fluoro-L-DOPA in rats, monkeys and humans

Journal Article · Mon Jan 01 00:00:00 EST 1990 · Life Sciences; (USA)

DOI:https://doi.org/10.1016/0024-3205(90)90228-J· OSTI ID:6526813

Melega, W P; Hoffman, J M; Luxen, A; Nissenson, C H.K.; Phelps, M E; Barrio, J R ^[1]

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1. UCLA School of Medicine, Los Angeles, CA (USA)

After carbidopa pretreatment, FDOPA plasma metabolite profiles in all three species revealed extensive metabolism of FDOPA to 3-O-methyl-6-({sup 18}F)-fluoro-L-DOPA (3-OMFD). In humans, there were significant increases in FDOPA plasma levels for 30 min and in 3-OMFD levels for 120 min after FDOPA administration. 6-({sup 18}F)Fluorodopamine sulfate and ({sup 18}F)fluoro-homovanillic acid levels were decreased, while at all times, free 6-({sup 18}F)-fluorodopamine (FDA) and 6-({sup 18}F)-3-4 dihydroxy-phenylacetic acid (FDOPAC) were not detected. In rat brain, the FDOPA metabolite profile at 30 min was significantly altered by carbidopa pretreatment; increases were noted for striatum FDA and 3-OMFD, and for cerebellum FDOPA and 3-OMFD. Thus, carbidopa pretreatment increased FDOPA plasma levels for a given FDOPA dose and essentially restricted peripheral FDOPA metabolism to 3-OMFD formation. The increase in FDOPA bioavailability to the brain resulted in greater selective FDA accumulation in striatum. As such, carbidopa pretreatment for FDOPA-positron emission tomography studies will significantly increase the amount of radioactivity that can be attributable to FDA in cerebral regions of interest.

• OSTI ID: 6526813
• Journal Information: Life Sciences; (USA), Vol. 47:2; ISSN 0024-3205
• Country of Publication: United States
• Language: English

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