Does Dopamine Inhibit or Stimulate Prolactin Release In Vitro ? The Effects of Dopamine Concentration and Duration of In Vivo Estradiol Treatment

Abstract

Prolactin release was examined from pituitary explants of ovariectomized, Fischer 344 rats at various times of estradiol treatment. The explants were acutely exposed to concentrations of dopamine from 0 to 10^-4 M and the concentration of prolactin in the resulting incubation medium was determined by radioimmunoassay. At 1 and 2 weeks of estradiol treatment, prolactin release from explants of Fischer 344 rats was not inhibited by 10^-6 or 10^-5 M dopamine when compared with release from explants exposed to no dopamine, whereas dopamine at doses of 10^-7 and 10^-8 M significantly stimulated prolactin release. By 3 or 4 weeks of estradiol treatment, the stimulatory effects of the low doses of dopamine were not evident and higher doses significantly inhibited prolactin release. These data indicate that dopamine can inhibit, stimulate, or produce no change in prolactin secretion and that these effects depend upon the concentration of dopamine used and the duration of estradiol treatment to which the animals are subjected.