Extensive ultrastructural changes in rat mammotrophs following administration of the dopamine agonist ergocristine-reflecting inhibition of prolactin release.

We have demonstrated an extensive reorganization of organelles in mammotrophs immediately following administration of ergocristine (a dopamine agonist) to estradiol-primed male rats. Our ultrastructural findings are consistent with our previous results that ergocristine can block prolactin release without any noticeable latent period. Following three-week priming of male rats with estradiol implants, ergocristine was administered by a bolus injection through an indwelling cannula. Within two min of its administration, ergocristine induced dramatic changes in the ultrastructure of mammotrophs, i.e., (1) increased numbers of secretory granules, (2) peripheral relocation of rough endoplasmic reticulum which tends to sequester secretory granules, (3) change in location of nucleus and (4) increased numbers of intracellular bodies associated with secretory granules. We suggest that the extensive ultrastructural changes that occurred in such a short period following ergocristine administration may be indications of specific factors associated with blockage of hormone release.