To characterize the functional aspect of
prolactin (Prl) cells coexisting with
corticotroph adenomas,
pituitary adenoma cells obtained from a patient with
Cushing's disease and a patient with Nelson's syndrome, who were associated with
hyperprolactinaemia, were cultured in monolayer and their Prl responses to various
secretagogues were compared with those of
prolactinoma cells in culture. Immunohistochemistry performed in one of these two
adenomas demonstrated the presence of Prl-containing cells in addition to
ACTH cells. When
ACTH-Prl
adenoma cells were exposed to ovine
corticotrophin-releasing factor (CRF), a dose-dependent increase in both
ACTH and Prl secretion was observed, which was blocked by coincubation with
hydrocortisone. In contrast, no stimulatory effect of CRF on Prl release was observed in all of the experiments using
prolactinoma cells.
Thyrotrophin-releasing
hormone, which consistently stimulated Prl secretion in
ACTH-Prl
adenomas, was effective in triggering Prl release in only 25% of the
prolactinomas. Exposure of the cultured cells to
lysine vasopressin,
growth hormone-releasing factor and
vasoactive intestinal peptide resulted in an increase in
ACTH and Prl secretion in one
ACTH-Prl
adenoma, however, none of the
prolactinomas responded to these stimuli to secrete Prl.
Dopamine and
somatostatin, on the other hand, uniformly suppressed Prl secretion from
ACTH-Prl
adenomas as well as from
prolactinoma cells. These results suggest that the mode of Prl secretion by mixed
ACTH-Prl
pituitary adenomas is not identical to that by pure
prolactinomas and is, at least in part, common to that of
ACTh secretion.