AJP - Endocrinology and Metabolism, Vol 273, Issue 3 E593-E598, Copyright © 1997 by American Physiological Society
Dopamine requires ascorbic acid to be the prolactin release-inhibiting factor
S. H. Shin, F. Si, A. Chang and G. M. Ross
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
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.
