Evidence for L-dopa relevant to modulation of sympathetic activity in the rostral ventrolateral medulla of rats.
By microdialysis in the rostral ventrolateral medulla (RVLM) of anesthetized rats, the spontaneous L-3,4-dihydroxyphenylalanine (DOPA) release was partially Ca(2+)-dependent and tetrodotoxin-sensitive and was markedly reduced by alpha-methyl-p-tyrosine (alpha-MPT; 200 mg/kg, i.p.). K+ (50 mM) Ca(2+)-dependently evoked L-DOPA. By microinjections into unilateral RVLM, L-DOPA (30-300 ng) produced dose-dependent hypertension and tachycardia 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 (1.5 micrograms), a competitive L-DOPA antagonist. D-DOPA, dopamine, noradrenaline or adrenaline (300 ng) produced no effect. Furthermore, L-DOPA methyl ester alone microinjected into bilateral RVLM (2 micrograms x 2) produced prolonged hypotension and bradycardia, which were abolished by alpha-MPT. These data suggest that L-DOPA is relevant to modulation of sympathetic activity in the rat RVLM.
Yue
J L
JL
Department of Pharmacology, Yokohama City University School of Medicine, Japan.
Goshima
Y
Y
Miyamae
T
T
Misu
Y
Y
D000818:Animals; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D001794:Blood Pressure / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry; D006339:Heart Rate / Q000187:drug effects; D006834:Hydrazines / Q000494:pharmacology; D007980:Levodopa / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D008526:Medulla Oblongata / Q000378:metabolism / Q000502:physiology*; D008781:Methyltyrosines / Q000494:pharmacology; D017551:Microdialysis; D008845:Microinjections; D016627:Oxidopamine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013564:Sympathetic Nervous System / Q000378:metabolism / Q000502:physiology*; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors; D019805:alpha-Methyltyrosine
D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D006834:Hydrazines; D008781:Methyltyrosines; D007980:Levodopa; D019805:alpha-Methyltyrosine; D016627:Oxidopamine; C004297:3-hydroxybenzylhydrazine; D014446:Tyrosine 3-Monooxygenase