Ultrastructural morphology of nontumorous prolactin cells in human pituitaries harboring prolactin-producing adenoma.

To study the effect of hyperprolactinemia on nontumorous prolactin cells, their morphology was investigated by transmission electron microscopy and morphometry in the nontumorous portion of seven human pituitaries containing prolactin-producing adenoma. For cell identification, immunoelectron microscopy was applied using the immunogold labelling method. In five cases, nontumorous prolactin cells demonstrated features of inactivity, whereas in two cases they showed morphological features of active hormone secretion. Our findings are consistent with the view that prolactin regulates its own release from prolactin cells in the anterior pituitary via the short loop negative feedback mechanism. Hyperprolactinemia presumably activates the short loop feedback mechanism resulting in inhibition of nontumorous prolactin cell. However, in two cases, hyperactivity of nontumorous prolactin cells was observed suggesting a dysfunction of the feedback mechanism.