The stimulatory and inhibitory effects of quinpirole hydrochloride, D2-dopamine receptor agonist, on secretion of prolactin as assessed by the reverse hemolytic plaque assay.
Recent findings indicate that low concentrations of dopamine (DA) stimulate the secretion of prolactin (PRL) in vitro. In this study, we found that low concentrations of the highly-specific DA D2 receptor agonist, quinpirole hydrochloride (LY) stimulate PRL secretion in female rats, assessed by reverse hemolytic plaque assay. Low concentrations of LY (10(-12), 10(-10) M) increased the mean plaque area and increased the fraction of lactotrophs forming large plaques. On the other hand, higher concentrations of LY (10(-8), 10(-6) M) reduced the mean plaque size. Treatment of cells with 10(-6) M LY produced a unimodal distribution of small plaques. Low concentrations of LY (10(-12), 10(-10) M) with TRH (10(-7) M) produced an additive effect on TRH-induced PRL release. Pretreatment of anterior pituitary cells with pertussis toxin (30 ng/ml, 24 h) inhibited the LY-stimulated increase in plaque area. These findings indicate that very low concentrations of DA agonist stimulate the secretion of PRL per cell, and that the stimulatory effects of DA agonist on PRL secretion may be mediated by a pertussis toxin-sensitive G protein.
Niimi
M
M
Department of Clinical Laboratory, Kagawa Medical School, Japan.
Takahara
J
J
Sato
M
M
Murao
K
K
Kawanishi
K
K
D000704:Analysis of Variance; D000818:Animals; D015259:Dopamine Agents / Q000494:pharmacology*; D004873:Ergolines / Q000494:pharmacology*; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology; D006462:Hemolytic Plaque Technique; D066298:In Vitro Techniques; D037342:Pertussis Toxin; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011388:Prolactin / Q000187:drug effects* / Q000378:metabolism; D019257:Quinpirole; D051381:Rats; D017208:Rats, Wistar; D013973:Thyrotropin-Releasing Hormone / Q000502:physiology*; D010566:Virulence Factors, Bordetella
D015259:Dopamine Agents; D004873:Ergolines; D010566:Virulence Factors, Bordetella; D019257:Quinpirole; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins