Action of thymoxamine on mydriasis induced by levodopa and dopamine.
Eye-drops of levodopa and dopamine induce pupillary dilatation which is inhibited by thymoxamine, an alpha-adrenergic blocking drug. This indicates that the mydriatic action of levodopa and dopamine involves excitation of alpha-adrenergic receptors of the dilator pupillae muscle. Such a conclusion is in accord with the previously expressed suggestion that levodopa is rapidly converted to dopamine, which displaces noradrenaline from adrenergic nerve endings.The findings that dopamine exerts alpha-adrenergic effects at the periphery may be construed as evidence in support of the view that the hypotensive action of levodopa is mediated via the central nervous system.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D002490:Central Nervous System / Q000187:drug effects; D004295:Dihydroxyphenylalanine / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004106:Dilatation; D004298:Dopamine / Q000096:biosynthesis; D018492:Dopamine Antagonists; D006801:Humans; D006873:Hydroquinones / Q000494:pharmacology*; D007498:Iris / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D011680:Pupil / Q000187:drug effects*; D011941:Receptors, Adrenergic / Q000187:drug effects; D013565:Sympatholytics / Q000494:pharmacology*
D000317:Adrenergic alpha-Antagonists; D018492:Dopamine Antagonists; D006873:Hydroquinones; D011941:Receptors, Adrenergic; D013565:Sympatholytics; D004295:Dihydroxyphenylalanine; D004298:Dopamine; D009638:Norepinephrine