Muscarinic regulation of basal versus thyrotropin-releasing hormone-induced prolactin secretion in rat anterior pituitary cells. differential roles of nitric oxide and intracellular calcium mobilization.
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), 17beta-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 microM forskolin) or Ca(2+) (1 microM 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 microM) and thapsigargin (1 microM), but abrogated by the nitric oxide synthase inhibitor (300 microM 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.
Pu
H F
HF
Institute of Physiology, National Yang-Ming University, Shih-Pai, Taipei, Taiwan, Republic of China.
Tan
S K
SK
Chen
H L
HL
Jea
J C
JC
Liu
T C
TC
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002120:Calcium Channel Agonists / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D009474:Neurons / Q000737:chemistry / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D037342:Pertussis Toxin; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000097:blood / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000502:physiology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D002120:Calcium Channel Agonists; D015220:Calcium Channels; D011976:Receptors, Muscarinic; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D009569:Nitric Oxide; D013973:Thyrotropin-Releasing Hormone; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D011388:Prolactin; D000242:Cyclic AMP; D037342:Pertussis Toxin; D000109:Acetylcholine; D002118:Calcium