Journal of neuroendocrinology
-
J. Neuroendocrinol. · Feb 1992
Inhibition of prolactin release by gonadotropin-releasing hormone-associated Peptide in benign, dopamine-sensitive and in malignant, dopamine-resistant pituitary tumors.
Since the gonadotropin-releasing hormone-associated peptide (GAP) has been reported to be capable of inhibiting prolactin release from normal lactotrophs, with the present study we have examined the in vitro effects of GAP on prolactin release in an estrone-induced, dopamine-sensitive rat pituitary adenoma and two malignant, transplantable and dopamine-resistant rat pituitary tumors, 7315a and MtTW15. Enzymatically dispersed cells obtained from the three types of tumor were cultured in multiwell dishes for 4 days. On the fifth day, the cells were exposed for 4 h to human GAP 1-56 or to the analog GAP 42-56 or to rat GAP 1-53, at various concentrations. ⋯ Furthermore, in adenomatous cells, the inhibitory effects of these peptides were suppressed by pretreatment of the cells with pertussis toxin. These findings indicate that GAP is capable of inhibiting prolactin release even in dopamine-resistant pituitary tumors. This inhibition is exerted through a pertussis toxin-sensitive G-protein-dependent signaling mechanism in adenomatous cells.