L-dopa-induced hypotension: depression of spinal sympathetic neurons by release of 5-hydroxytryptamine.
In studies designed to determine the respective functional roles of two bulbospinal monoaminergic pathways to sympathetic preganglionic neurons, both L-dopa and precursors of 5-HT depressed transmission through excitatory spinal reflex and bulbospinal sympathetic pathways. Transmission through spinal reflex pathways was secondarily enhanced after L-dopa. Pharmacological tests indicated mediation of these affects by monoamines. After antagonism or depletion of central 5-HT, L-dopa only enhanced transmission through both pathways. The results indicate that hypotension and other sympathoinhibitory effects of L-dopa are produced at the spinal level by release of 5-HT from terminals of bulbospinal 5-HT pathways that are inhibitory to sympathetic preganglionic neurons. The excitatory effects of L-dopa are apparently mediated by release of catecholamines from bulbospinal noradrenergic pathways that are excitatory.
D006916:5-Hydroxytryptophan / Q000494:pharmacology; D000818:Animals; D001339:Autonomic Fibers, Preganglionic / Q000187:drug effects*; D001794:Blood Pressure / Q000187:drug effects*; D002415:Cats; D007980:Levodopa / Q000494:pharmacology*; D008526:Medulla Oblongata / Q000187:drug effects; D009433:Neural Inhibition / Q000187:drug effects; D012018:Reflex / Q000187:drug effects; D012701:Serotonin / Q000502:physiology*; D013116:Spinal Cord / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects; D014364:Tryptophan / Q000494:pharmacology
D012701:Serotonin; D007980:Levodopa; D014364:Tryptophan; D006916:5-Hydroxytryptophan