An L-DOPA-like depressor action of L-threo-dihydroxyphenyl-serine in the rat caudal ventrolateral medulla.
We have proposed that L-3,4-dihydroxyphenylalanine (L-DOPA) is a neurotransmitter and/or neuromodulator in the central nervous system (1). In this study, we investigated whether or not L-threo-dihydroxyphenylserine (L-threo-DOPS), a synthetic amino acid structurally related to L-DOPA, microinjected into the caudal ventrolateral medulla (CVLM) and the rostral ventrolateral medulla (RVLM) shows cardiovascular actions similar to those of L-DOPA in anesthetized rats. When L-threo-DOPS was microinjected into CVLM, it produced dose-dependent (0.01-3 ng) depressor and bradycardic responses. D-threo-DOPS (3 ng) produced no effect. The responses to L-threo-DOPS (1 ng) were almost completely blocked by L-DOPA methyl ester (1 microg), a competitive antagonist for L-DOPA, supporting the existence of an L-threo-DOPS-sensitive recognition site for L-DOPA in CVLM. Microinjection of L-threo-DOPS into RVLM, however, showed no effect (0.001-100 ng), which contrasted with the cardiopressor action of L-DOPA applied in RVLM. In RVLM, there may exist an L-threo-DOPS-insensitive recognition site for L-DOPA.
Furukawa
N
N
Department of Pharmacology, Yokohama City University School of Medicine, Yokohama, Japan.
Goshima
Y
Y
Miyamae
T
T
Nishihama
M
M
Okumura
F
F
Fujita
K
K
Misu
Y
Y
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D015103:Droxidopa / Q000494:pharmacology*; D018698:Glutamic Acid / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects*; D007980:Levodopa / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology*; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D008845:Microinjections; D009928:Organ Specificity; D051381:Rats; D017208:Rats, Wistar
D018698:Glutamic Acid; D007980:Levodopa; D015103:Droxidopa