Transmitter-like L-3,4-dihydroxyphenylalanine tonically functions to mediate vasodepressor control in the caudal ventrolateral medulla of rats.
By microdialysis in the unilateral caudal ventrolateral medulla (CVLM) of anesthetized rats, the spontaneous L-3,4-dihydroxyphenylalanine (L-DOPA) release was in part tetrodotoxin-sensitive or Ca(2+)-dependent and was abolished by i.p. alpha-methyl-p-tyrosine (alpha-MPT), a tyrosine hydroxylase inhibitor. High K+ (50 mM) Ca(2+)-dependently evoked L-DOPA. By unilateral microinjections into the CVLM, L-DOPA (10-100 ng) produced dose-dependent, marked hypotension and bradycardia similarly in rats untreated, treated with i.p. 3-hydroxybenzylhydrazine, a central DOPA decarboxylase inhibitor, or with i.v.t. 6-hydroxydopamine. These responses were antagonized by L-DOPA methyl ester, a competitive L-DOPA antagonist. A depressor response to dopamine or noradrenaline (100 ng) was far smaller and slower in onset than that to L-DOPA (30 ng). D-DOPA (100 ng) produced no effect. Furthermore, L-DOPA methyl ester microinjected into bilateral CVLM produced some hypertension and tachycardia, which were markedly reduced by alpha-MPT. Transmitter-like L-DOPA tonically functions to mediate vasodepressor control in CVLM of rats.
Yue
J L
JL
Department of Pharmacology, Yokohama City University School of Medicine, Japan.
Goshima
Y
Y
Misu
Y
Y
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D004295:Dihydroxyphenylalanine / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism; D004563:Electrochemistry; D006439:Hemodynamics / Q000187:drug effects*; D007980:Levodopa / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D017551:Microdialysis; D008845:Microinjections; D009638:Norepinephrine / Q000378:metabolism; D016627:Oxidopamine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013238:Stereotaxic Techniques
D007980:Levodopa; D004295:Dihydroxyphenylalanine; D016627:Oxidopamine; D004298:Dopamine; D009638:Norepinephrine