In vitro expression of tyrosine hydroxylase by a subpopulation of rat melanotrophs is down-regulated by dopamine.
Some rat melanotrophs express in vivo tyrosine hydroxylase mRNA. In this report we show, by Western-blotting, that cultures of adult rat melanotrophs, but not adenohypophyseal cells, express tyrosine hydroxylase. Immunocytochemical analyses confirmed the existence of a subpopulation of melanotrophs expressing tyrosine hydroxylase. Bromocryptine (2.5 x 10(-7) M), a D2 dopamine agonist, down-regulated melanotroph tyrosine hydroxylase expression in a time-dependent manner; initial effect was detected at 15 h and maximum at 3 days treatment (reduction to about 40% of control values). Down-regulation at 3 days was dose-dependent (ED(50) around 2 x 10(-9) M). This decrease was reversed by sulpiride, a D2 dopamine antagonist. The cell number was slightly increased by bromocryptine treatment. These data suggest tyrosine hydroxylase expression in melanotrophs being under tonic inhibitory control by dopamine innervation in vivo.
Niquet
J
J
Departamento de Genetica y Fisiologia Molecular, Instituto de Biotecnologia, Universidad Nacional Autonoma de Mexico, Cuernavaca, Mexico.
Charli
J
J
D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology; D018929:Cell Culture Techniques; D004298:Dopamine / Q000378:metabolism*; D018491:Dopamine Agonists / Q000494:pharmacology; D007150:Immunohistochemistry; D009074:Melanocyte-Stimulating Hormones / Q000187:drug effects* / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects* / Q000378:metabolism*; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics* / Q000378:metabolism*
D018491:Dopamine Agonists; D012333:RNA, Messenger; D001971:Bromocriptine; D009074:Melanocyte-Stimulating Hormones; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine