Dopamine requires ascorbic acid to be the prolactin release-inhibiting factor.
A high concentration of dopamine (10(-6) mol/l) inhibited prolactin release for < 60 min during a 2-h perifusion period by use of primary cultured pituitary cells. However, when dopamine (10(-6) mol/l) and control medium were alternately perifused, dopamine inhibited prolactin release for a longer period, indicating that the inability of dopamine to sustain an inhibitory action is likely caused by decreased sensitivity of the lactotrophs to dopamine. When 3 x 10(-7) mol/l dopamine was perifused, prolactin release was inhibited for only 15 min, and the rate of prolactin release was decreased to a nadir by addition of ascorbic acid (10(-4) mol/l) 15 min after the start of dopamine perifusion. Dopamine decreased density of dopamine D2 receptors, and ascorbic acid inhibited the receptor downregulation in GH4ZR7 cells. These results support our hypothesis that dopamine requires a supplementary agent to be the prolactin release-inhibiting factor and that the supplementary agent is ascorbic acid.
Shin
S H
SH
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
Si
F
F
Chang
A
A
Ross
G M
GM
D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D002460:Cell Line; D002478:Cells, Cultured; D004298:Dopamine / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011981:Receptors, Prolactin / Q000378:metabolism / Q000502:physiology*; D013134:Spiperone / Q000378:metabolism; D013997:Time Factors
D011981:Receptors, Prolactin; D013134:Spiperone; D011388:Prolactin; D001205:Ascorbic Acid; D004298:Dopamine