Muscarinic Regulation of Basal versus Thyrotropin-Releasing Hormone-Induced Prolactin Secretion in Rat AnteriorPituitary Cells

• Published in: Neuroendocrinology Vol. 70; no. 5; pp. 324 - 331
• Main Authors: Pu, Hsiao-Fung, Tan, Sai-Koong, Chen, Hsing-Liang, Jea, Jing-Chi, Liu, Tsuei-Chu
• Format: Journal Article
• Language: English
• Published: Basel, Switzerland 01.05.1999
• Subjects: Pituitary Transduction; Ca2+ channels; Thyrotropin-releasing hormone; Prolactin; Nitric oxide; Forskolin; Bay K; Acetylcholine
• ISSN: 0028-3835; 1423-0194
• DOI: 10.1159/000054493

Acetylcholine (ACh), synthesized in the pituitary, can act locally to modulate pituitary function. We used rat primary anterior pituitary (AP) cells to investigate how ACh affects pituitary prolactin (PRL) secretion in the presence or absence of known PRL regulators: thyrotropin-releasing hormone (TRH), 17β-estradiol (E 2 ) and triiodothyronine (T 3 ). Cultured AP cells were prepared from ovariectomized rats and pretreated with diluent, 0.6 nM E 2 , 10 nM T 3 , or E 2 plus T 3 for 5 days, then challenged with various doses of ACh or muscarinic receptor agonists (oxotremorine or carbachol) and TRH (100 nM) for 20 min. Significant ACh (10 –5 M) suppression of both basal and TRH-induced PRL secretion was not evident in diluent-, E 2 - or T 3 -pretreated cells, but observed only in cells pretreated with both E 2 and T 3 . Moreover, in E 2 plus T 3 -pretreated cells, oxotremorine and carbachol, like ACh (10 –7 –10 –5 M), suppressed both responses in a dose- related manner. Pertussis toxin (PTX; 100 ng/ml) as well as atropine (a muscarinic receptor antagonist; 1 mM) blocked these effects of cholinomimetics. ACh also inhibited both PRL responses elicited by drugs elevating intracellular cAMP (10 µM forskolin) or Ca 2+ (1 µM Bay K-8644) in a PTX-sensitive manner. ACh inhibition of basal PRL secretion was unaltered by intracellular Ca 2+ mobilization blockers, TMB-8 (100 µM) and thapsigargin (1 µM), but abrogated by the nitric oxide synthase inhibitor (300 µM L-NAME). ACh inhibition of TRH-induced PRL secretion was accentuated by TMB-8 and alleviated by thapsigargin or L-NAME. In summary, muscarinic inhibition of either basal or TRH-induced PRL secretion was augmented by E 2 and T 3 , and involved the PTX-sensitive cAMP/Ca 2+ pathways. Furthermore, nitric oxide mediated the basal rather than TRH-induced PRL response to ACh, whereas the intracellular Ca 2+ mobilization concerned the TRH-induced rather than the basal PRL response to ACh. Thus, ACh synthesized in the AP appears to inhibit basal vs. TRH-induced PRL secretion via different mechanisms.